Up for discussion in this thread is (in no particular order):


Caster and Caster change with suspension travel
Camber and Camber change with suspension travel
Toe and Toe change with suspension travel (aka bump-steer)
Track Width and Track Width change with suspension travel (aka Scrub or Lateral Scrub but I don't like to use those terms because of the confusion with Scrub Radius)
Wheelbase and Wheelbase change with suspension travel
Kingpin Inclination (aka Steering Axis Inclination)
Scrub Radius (aka Kingpin Offset)
Trail (aka Caster Trail)
Ackerman (Toe-Change with steering)
Instant Center (front view and side view)
Roll Center
Anti-Dive / Pro-Dive
Splay Angle (Angling of the control arm mounts as viewed from above)
Sprung Mass
Unsprung Mass
% Front Mass
Spring Rate
Damping
Shock / Coil-Over motion ratios (and change with suspension travel)
Wheel Travel


Some definitions are here if you don't know them
http://autospeed.com/cms/article.html?&A=2895

thanks for starting this. I'll try to answer as many questions as possible. This will be good for the guys coming from the rock crawling backround.

This thread will for sure get me in trouble, I just hope it doesn't go in the shitter too fast.

The only thing on the list I think worth really discussing/arguing about is roll center as classically defined. That idea should be thrown in the trash for independent a-arm suspensions as far as I'm concerned. This is not my idea alone, there are many much more well known than me teaching this. Often it's a good approximation (somewhat by chance), but in reality it is not the point the chassis rolls about and it is not a force center which leaves one asking "what's the reason for it?", which is the correct question. Dan, your thoughts?

The rest of the parameters are just that. They have concrete, useful definitions and beyond that one can defend which adjustment of that parameter is best and for what reason. Sometimes it's important and sometimes it just isn't dominating like all the scrub radius talk in the other thread. I have my opinions and my reasonings, but who's to say someone else's isn't just as effective? I guess that's what we'll find out in this thread!

I'm kinda with you on the whole kinematic roll center thing. I take it you have read Mitchell's work on Force Based Roll Centers? I.e. SAE Paper 2006-01-3617. There is some mention here:
http://www.mitchellsoftware.com/ForceBasedRC_1.htm

I'm kinda with you on the whole kinematic roll center thing. I take it you have read Mitchell's work on Force Based Roll Centers? I.e. SAE Paper 2006-01-3617. There is some mention here:
http://www.mitchellsoftware.com/ForceBasedRC_1.htm

I haven't read that. But, I will have after this evening.

So everyone that mentions the geometric roll center in this thread gets this --->:flipoff2: :laughing:

Edit: I just checked that link, and I'm also not a big fan of force-based roll centers for the same reasons. We'll get more into it later but my whole point is little attention needs to be paid to either of these roll centers..
Edit2: I am familiar with the idea, but never read the paper.
Edit3: I have now read it.

I agree with many points brought up. The problem is the force based roll center suffers the same ills as the kinematic one. It's more difficult to calculate and is just a modification on the classic roll center. You can analyze all those forces he discusses with IC's alone, which is what I do. I'm also a big fan of the terms "pro-roll" and "anti-roll" and find it to be a much more normalized expression of independent suspension parameters just like anti-squat and anti-dive are for the side view. I admit, I do use kinematic roll center as a convenient design/estimation tool for dirty calcs and giggles, but its usefulness really does end there! JMO.

Hey looks like a good thread and I'll have to study the link when I'm not at work lol!

Jason :)

There are some good threads on RDC about some of these things. I'll try to round-up some relevant links later.

How about this (With editing by me in []):
...[Track Width Change] is a function of camber change and arm length. [TWC] does not mean [anything] on a dirt vehicle and it is NOT a parameter a fabricator should build around. Now a street driven prerunner/dd is different. With a stock frame one can only make the arms so long and the camber change so dramatic to keep the [TWC] minimal and not become ineffective to the point that you are blowing out wheel bearings and looking ridiculous...I'm guessing that is how he meant it.

This was a good idea. I didn't want to post in frog's thread anymore, it was getting off-topic.
The whole thing about scrub radius started by 'someone' calculating suspension geometry off a photograph posted on the internet. Anyone here in the habit of doing that?
I'm sure he will be stalking over here shortly......
Please do post any and all relevant links-thanks!

In all reality there are some suspension parameters that you can close one eye, hold your thumb out in front of you, and say "that's too much". My "calibrated eye-ball" would tell me that his scrub radius was every bit of 4". I'm sure scaling it off a picture would get you a bit closer then just an eye-ball even with some distortion.

I would agree that in person you can eyeball some alignment angles. I disagree that you can do it in a photograph on the internet on your computer screen and then transfer it to another computer program and analyze it with any reliable degree of accuracy.
'frog' has already stated it is nowhere near 4". Respectfully I would submit that he would know and we don't. Just because someone doesn't spend the time here trying to impress people doesn't mean that someone is not impressive. Of course the opposite can be true also, but I have ALOT more patience than some have displayed recently.
What would be truly helpful here would be some examples of real life Trophy Trucks' alignment specs -if that is even possible.

i kept out of the other thread but it did have me wondering.

to me it seems that scrub radius on a 2wd off road vehicle isn't that big of an issue. the wheels are allowed to spin freely as fast or as slow as they need to. i could see it being a problem when sitting still, standing on the brakes and trying to turn the wheel but not while moving. when rock crawling in 4wd i can see it being an issue, especially while the differential is locked. i am not an alignment specialist or a steering/suspension engineer. i'm just a garage hack so i am sure some one will correct me but that is how i see it.

and while i am thinking about scrub radius, was every one calling this guy out on it: http://pirate4x4.com/forum/showthread.php?t=615419 ? i am going to go back an reread the thread but i don't remember it mentioned. i think that is going to cause some serious binding especially if he is running a spool or welded diff. maybe no one harassed him about it because of his awesome fabrication on that build.

i just don't see it being that big of a deal on a 2wd dirt truck but i could be wrong.

...What would be truly helpful here would be some examples of real life Trophy Trucks' alignment specs -if that is even possible.Not from me because of non-disclosure agreements and trade secrets:flipoff2: I'm just trying to prompt some discussion.

...to me it seems that scrub radius on a 2wd off road vehicle isn't that big of an issue. the wheels are allowed to spin freely as fast or as slow as they need to...The problem is hitting bumps with one wheel. The larger the scrub radius (and trail but that is another story) the greater the torque on the upright which will in turn put more stress through the entire steering system and ultimately to the steering wheel.

The problem is hitting bumps with one wheel. The larger the scrub radius (and trail but that is another story) the greater the torque on the upright which will in turn put more stress through the entire steering system and ultimately to the steering wheel.

now that makes total sense.

Not from me because of non-disclosure agreements and trade secrets:flipoff2: I'm just trying to prompt some discussion.

That's what I was afraid of.:laughing:
But I'm gathering that no scrub radius is considered ideal in this case?

There are many things about suspension geometry (at least for off-road vehicles) that would some people consider 'ideal' and other people believe the polar-opposite to be true. I think most people would agree that an excessive scrub radius would be bad, but some people shoot for zero and others design a little into their suspension (on purpose).

There are many things about suspension geometry (at least for off-road vehicles) that would some people consider 'ideal' and other people believe the polar-opposite to be true. I think most people would agree that an excessive scrub radius would be bad, but some people shoot for zero and others design a little into their suspension (on purpose).

i agree with this. i'm not saying it has to be zero. i'm saying that's a good starting point some positive or some negative can have good effects depending on other geometry.

Scrub radius is a function of camber change and arm length. SR does not mean SHIT on a dirt vehicle and it is NOT a parameter a fabricator should build around. Now a street driven prerunner/dd is different. With a stock frame one can only make the arms so long and the camber change so dramatic to keep the SR minimal and not become ineffective to the point that you are blowing out wheel bearings and looking ridiculous. Why don't you go read up on suspension theory and STFU before you question my mentality:shaking:

this is wrong. scrub radius is a function of kingpin inclination and wheel offset....you could change your arm length and not change scrub radius if you put your mounts further inboard. since he's building from scratch and the mounts aren't a set parameter, you would use king pin inclination. on a dirt vehicle you would shoot for a scrub radius of 0. meaning at rest, a line drawn through your king pin would intersect the ground at the center of your tire. this plays a huge part in the contact patch of your tire. this is a huge issue for two wheel drive four wheelers. it also applies to anything with four wheels....:shaking:

I would agree that in person you can eyeball some alignment angles. I disagree that you can do it in a photograph on the internet on your computer screen and then transfer it to another computer program and analyze it with any reliable degree of accuracy.
'frog' has already stated it is nowhere near 4". Respectfully I would submit that he would know and we don't.

it's called scale. i can use his tire size and other angles in the photo as a scale to come up with a pretty accurate estimate. until i see a photo of a string running along both ball joints to the ground i'm not going to buy that he (frog) is even close to zero scrub radius. i'm a machinist, i do autocad 2d and autodesk inventor 3d parametric drawing...i'm pretty good. i didn't draw this up in microsoft paint.

to me it seems that scrub radius on a 2wd off road vehicle isn't that big of an issue. the wheels are allowed to spin freely as fast or as slow as they need to. i could see it being a problem when sitting still, standing on the brakes and trying to turn the wheel but not while moving. when rock crawling in 4wd i can see it being an issue, especially while the differential is locked. i am not an alignment specialist or a steering/suspension engineer.

it had to do with the contact patch of the tire while turning. you don't want your tires riding on the edges. it also dictates a lot of the "feel" of the steering wheel, and response to turning. having it correct for your application also helps keep the vehicle from pulling one direction if the braking forces on both sides aren't 100% equal.

it had to do with the contact patch of the tire while turning. you don't want your tires riding on the edges. it also dictates a lot of the "feel" of the steering wheel, and response to turning. having it correct for your application also helps keep the vehicle from pulling one direction if the braking forces on both sides aren't 100% equal.


i am not seeing how scrub radius effects the contact patch of the tire. i can see caster and king pin inclination effecting the contact patch while turning but not scrub radius. it seems to me that caster angle and kingpin inclination could change the contact patch while turning even with a zero scrub radius. i just can't picture in my head scrub radius causing the tires to ride on their edges while turning. i can see you braking point though.

i agree with this. i'm not saying it has to be zero. i'm saying that's a good starting point some positive or some negative can have good effects depending on other geometry.

Once you have designed this it's not adjustable so why is that a good "starting" point? It will be the finished product as far as scrub radius after it's built. Notice your next statement?

this is wrong. scrub radius is a function of kingpin inclination and wheel offset....you could change your arm length and not change scrub radius if you put your mounts further inboard. since he's building from scratch and the mounts aren't a set parameter, you would use king pin inclination. on a dirt vehicle you would shoot for a scrub radius of 0. meaning at rest, a line drawn through your king pin would intersect the ground at the center of your tire. this plays a huge part in the contact patch of your tire. this is a huge issue for two wheel drive four wheelers. it also applies to anything with four wheels....:shaking:

Contact patch of the tire is dependent upon alot of factors -like tire pressure and the tire design for example.:shaking:


it's called scale. i can use his tire size and other angles in the photo as a scale to come up with a pretty accurate estimate. until i see a photo of a string running along both ball joints to the ground i'm not going to buy that he (frog) is even close to zero scrub radius. i'm a machinist, i do autocad 2d and autodesk inventor 3d parametric drawing...i'm pretty good. i didn't draw this up in microsoft paint.

But you don't know a thing about photography-I'm pretty good at that.


it had to do with the contact patch of the tire while turning. you don't want your tires riding on the edges. it also dictates a lot of the "feel" of the steering wheel, and response to turning. having it correct for your application also helps keep the vehicle from pulling one direction if the braking forces on both sides aren't 100% equal.

Directional stability can be influenced with other angles very easily. You would know that if you ever did an alignment on a vehicle.
Tires riding on the edges or not has nothing to do with scrub radius....:shaking:
Oh-correct my spelling for me will you. That's really important :shaking:
FYI -he was doing 'bro speak' in the other thread in an attempt at humor-which you seem to be sadly lacking.:shaking:
Don't they do machinist training at vocational school? Really impressive:shaking:

..this is wrong. scrub radius is a function of kingpin inclination and wheel offset....you could change your arm length and not change scrub radius if you put your mounts further inboard. since he's building from scratch and the mounts aren't a set parameter, you would use king pin inclination. on a dirt vehicle you would shoot for a scrub radius of 0. meaning at rest, a line drawn through your king pin would intersect the ground at the center of your tire. this plays a huge part in the contact patch of your tire. this is a huge issue for two wheel drive four wheelers. it also applies to anything with four wheels....:shaking:...Go back up to post 8 in this thread. I am quite sure he confused Scrub Radius for what some people call Scrub but I choose to call Track Width Change because of the confusion (those who call it scrub substitute KPI Offset or Steering Axis Offset for Scrub Radius).

If you read it in this light he might actually make a bit of sense.
http://www.pirate4x4.com/forum/showpost.php?p=8145665&postcount=8

i am not seeing how scrub radius effects the contact patch of the tire. i can see caster and king pin inclination effecting the contact patch while turning but not scrub radius. it seems to me that caster angle and kingpin inclination could change the contact patch while turning even with a zero scrub radius. i just can't picture in my head scrub radius causing the tires to ride on their edges while turning. i can see you braking point though.Put a vehicle on corner weight scales with turn tables under the front tires. Scrub radius can effect how much weight is jacked diagonally. It will also change the wheelbase on each side.

Directional stability can be influenced with other angles very easily. You would know that if you ever did an alignment on a vehicle.
Tires riding on the edges or not has nothing to do with scrub radius....:shaking:
Oh-correct my spelling for me will you. That's really important :shaking:
FYI -he was doing 'bro speak' in the other thread in an attempt at humor-which you seem to be sadly lacking.:shaking:
Don't they do machinist training at vocational school? Really impressive:shaking:

you don't read well do you? i didn't say directional stability wasn't influenced by anything else, in fact numerous times i've said that scrub radius is just one part of the equation. if your king pin inclination is not vertical (which it should not be) and you have a large positive or negative scrub radius during a turn, the tire is pivoting on a point inside or outside the tire. this is going to change the amount of effort it takes to turn, the amount of feedback you get. it has to do with the point the tire is rotating around, and the amount of tread to the right and left of that point. it changes the forces on the inside and outside of the contact patch and will cause the tire to wear unevenly, among the other steering changes. this is important to vehicles that turn...

last i checked, they don't teach exotic alloy, aerospace, 3D CNC machining at any vocational schools i know of. besides, i'm a manufacturing engineer, machining is just a small aspect of that.

I won't even go into the lack of spelling skills displayed- but would like to say that I honestly don't give much effort reading a poor grammer posting- it's like listening to someone who can't speak clearly-sometimes the message is misunderstood.

you brought up the spelling issue, i could care less. and i specifically said i was not referring to your "bro-tastic" post. feel free to point out all my spelling errors if you'd like. i guarantee, there aren't many. your sentence criticizing other's grammar is a run-on sentence with strange unneeded hyphens, and you misspelled grammar.....way to go.

Go back up to post 8 in this thread. I am quite sure he confused Scrub Radius for what some people call Scrub but I choose to call Track Width Change because of the confusion (those who call it scrub substitute KPI Offset or Steering Axis Offset for Scrub Radius).

If you read it in this light he might actually make a bit of sense.
http://www.pirate4x4.com/forum/showpost.php?p=8145665&postcount=8

i see what you're saying, i missed that post. although i'm skeptical that someone who claims to know suspensions wouldn't know the difference between those things, and if he can't clearly convey they idea to others, he should refrain from giving out advice.

i have another question. i have an IFS, IRS buggy. right now i'm trying to get the ackermann correct. i've done the typical trig. using the track width, wheel base stuff, etc. i also found your excel calculator. my question is, how much does rack location, rack length, and track rod length and angle affect ackermann? (it's a low power, low speed buggy)

This was a good idea. I didn't want to post in frog's thread anymore, it was getting off-topic.
The whole thing about scrub radius started by 'someone' calculating suspension geometry off a photograph posted on the internet. Anyone here in the habit of doing that?
I'm sure he will be stalking over here shortly......
Please do post any and all relevant links-thanks!

just go ahead and say my name i have no problem with that.

now that makes total sense.

dually dana 60 front axle with dually rims turned out...? hitting a bump.

could we talk about anti dive? and what exaclty defines it in a suspension?

In most race cars for the pavement-Ackermann is not really considered to be very important because of the amount of slip angle incurred in a turn kind of makes it irrelevant.

feel free to elaborate on this...i'm dying to here the explanation. it's actually incredibly important. crucial to tire wear, and steering response. for most pavement race cars they actually use negative ackermann, meaning the inside tire turns a larger radius than the outside. this has to do with the transfer of weight to the outside tire in high lateral g forces during turns...but i'd still like to hear your explanation of how it doesn't matter.

FYI-dimple dies are something fabricators with way too much time and money to spend on fancy equipment do to strengthen unnecessary sheetmetal plating they put on the roll cage to look cool to other fabricators.

sure, because using lighter gauge metal to save weight and adding 3 dimensional stability to it is stupid. and it takes super fancy equipment, like a male and female die and a hydraulic press. shit, it could cost you like 350.00-400.00 (depending on the hydraulic press) to start saving money on lighter material. besides, if you're fabricating a vehicle, 400.00 typically isn't much in terms of the budget. but yeah, most sheet metal gussets are unnecessary anyway...

could we talk about anti dive? and what exaclty defines it in a suspension?Same stuff as anti-squat (IC, CoG Height, Wheelbase), but multiplied by % front brakes. The next question is if you want to run anti-dive or pro-dive...

i have a question. i have an IFS, IRS buggy. right now i'm trying to get the ackermann correct. i've done the typical trig. using the track width, wheel base stuff, etc. i also found your excel calculator. my question is, how much does rack location, rack length, and track rod length and angle affect ackermann? (it's a low power, low speed buggy). is it enough to worry about, or should trigging it out get me as close as i need to be?

just go ahead and say my name i have no problem with that.

Did you post the photograph and calculate suspension geometry off that? Apparently you may not know the answer, you seem to think this was aimed at you, so I guess I will have to tell you. IT WAS NOT.

In all reality there are some suspension parameters that you can close one eye, hold your thumb out in front of you, and say "that's too much". My "calibrated eye-ball" would tell me that his scrub radius was every bit of 4". I'm sure scaling it off a picture would get you a bit closer then just an eye-ball even with some distortion.

I'm not going to play favorites here- I have to say :flipoff2::laughing:.
We can debate why it doesn't work- I'd rather we say lesson learned and forget about it. I am moving on.

My calibrated eye-ball works better in person:flipoff2:

feel free to elaborate on this...i'm dying to here the explanation. it's actually incredibly important. crucial to tire wear, and steering response. for most pavement race cars they actually use negative ackermann, meaning the inside tire turns a larger radius than the outside. this has to do with the transfer of weight to the outside tire in high lateral g forces during turns...but i'd still like to hear your explanation of how it doesn't matter.



sure, because using lighter gauge metal to save weight and adding 3 dimensional stability to it is stupid. and it takes super fancy equipment, like a male and female die and a hydraulic press. shit, it could cost you like 350.00-400.00 (depending on the hydraulic press) to start saving money on lighter material. besides, if you're fabricating a vehicle, 400.00 typically isn't much in terms of the budget. but yeah, most sheet metal gussets are unnecessary anyway...

I have some published sources that agree with my Ackermann theories. I will restate my theory in a different way. At speed the slip angles are so high and the steering angles are so low that Ackermann can be considered inconsequential. Of course there are exceptions to this, but offroad is not considered one of those exceptions as the slip angles are much greater than pavement.

Second point- that's my opinion and I'm sticking with it.

you don't read well do you? i didn't say directional stability wasn't influenced by anything else, in fact numerous times i've said that scrub radius is just one part of the equation.

You were referring to scrub radius there......

"if your king pin inclination is not vertical (which it should not be)"

Actually a vertical SAI (they have referred to it as SAI for over 30 years now)
is considered ideal for some uses, but difficult to acheive. A real life king pin front suspension example? VW Beetles have a vertical KPI. I have owned a KP equipped dune buggy since 1984. It's down in my garage right now.


"last i checked, they don't teach exotic alloy, aerospace, 3D CNC machining at any vocational schools i know of. besides, i'm a manufacturing engineer, machining is just a small aspect of that."

Thank you for making my point dumbass. You werer ridiculing my career as being the same as the highschool student learning how to do alignments in shop class. What I do has as much resemblance to that as your career to vocational school. Can you really be this stupid?



"you brought up the spelling issue, i could care less. and i specifically said i was not referring to your "bro-tastic" post. feel free to point out all my spelling errors if you'd like. i guarantee, there aren't many. your sentence criticizing other's grammar is a run-on sentence with strange unneeded hyphens, and you misspelled grammar.....way to go."

I wasn't even referring to your spelling and was making a dry joke about the "bro speak", but was sincere about it being difficult to read. I later found the bro speak posts to be quite hilarious actually, at least until you ruined it. You are taking way too many things personal here and going apeshit over stuff that doesn't even pertain to you. I am giving you enough insults as it is, at least refrain from taking insult to things not even pertaining to you.


I have to write stuff here outside the quotes so here it is....
Calm down dudes

I have some published sources that agree with my Ackermann theories. I will restate my theory in a different way. At speed the slip angles are so high and the steering angles are so low that Ackermann can be considered inconsequential. Of course there are exceptions to this, but offroad is not considered one of those exceptions as the slip angles are much greater than pavement.

Second point- that's my opinion and I'm sticking with it.In some of Carroll Smith's early books he stated negative Ackerman (toe-in with steering) was the way to go. In some of his later books he stated that every car that he put more Ackerman into turned better and that he had changed his mind even though the numbers didn't quite add up. Personally I have done everything from parallel steer to having the intersection 25% of the wheelbase in front of the rear axle centerline but never negative.

What does +/-/parallel Ackerman do to bump steer straight ahead and at full lock? Does anyone ever check bump steer at full lock?

FWIW I did some searching and asking around years ago about the spelling. The guy who the principal is named after was named Ackermann. Sometime it got Americanized and the 2nd "N" fell off. So now most texts call it Ackerman steering.:rolleyes: http://www.googlefight.com/index.php?lang=en_GB&word1=ackermann&word2=ackerman

[QUOTE=spork2367;8147647] "it's called scale. i can use his tire size and other angles in the photo as a scale to come up with a pretty accurate estimate. until i see a photo of a string running along both ball joints to the ground i'm not going to buy that he (frog) is even close to zero scrub radius. i'm a machinist, i do autocad 2d and autodesk inventor 3d parametric drawing...i'm pretty good. i didn't draw this up in microsoft paint."

You buying it now? Pretty good at what again?:flipoff2:
Do me a favor and examine that picture closer again. Do straight lines along the edges of the filing cabinet on the one side and something else on the left that would be considered straight up and down in real life. Notice how it angles in at the bottom? Notice how the wheels appear to be toe'd out alot? That's wide angle distortion and the distortion is worse in different parts of the photo. Telephoto lens give less distortion but have to be used at a distance and screw up depth perception. Normal cameras have these lens built in usually, if it has just one lens it will be a wide angle one. Let's call this lesson learned and move on. I have. Enough with the photo.

http://www.pirate4x4.com/forum/attachment.php?attachmentid=365128&d=1208193844

In some of Carroll Smith's early books he stated negative Ackerman (toe-in with steering) was the way to go. In some of his later books he stated that every car that he put more Ackerman into turned better and that he had changed his mind even though the numbers didn't quite add up. Personally I have done everything from parallel steer to having the intersection 25% of the wheelbase in front of the rear axle centerline but never negative.

What does +/-/parallel Ackerman do to bump steer straight ahead and at full lock? Does anyone ever check bump steer at full lock?

FWIW I did some searching and asking around years ago about the spelling. The guy who the principal is named after was named Ackermann. Sometime it got Americanized and the 2nd "N" fell off. So now most texts call it Ackerman steering.:rolleyes: http://www.googlefight.com/index.php?lang=en_GB&word1=ackermann&word2=ackerman

Negative Ackermann (sp lol) appears to be the way it was done back in the 60's in sports car racing but has since been done differently since Shelby's heydays. (forgive me Carroll!). There are other people who dismiss Ackermann as important in high speed racing. I realize it is still being used in different forms of racing, both negative and positive, but it depends on testing with driver,vehicle, and track being raced at, as to whether it is advantagous to do so or not.
Off road is it considered important? Due to the outrageously high slip angles I wouldn't see how it could be, but I'm open to new ideas.
I use the old school spelling of Ackermann because that's the man's name. I learned my stuff back when it was still spelled that way.:flipoff2:

i am not seeing how scrub radius effects the contact patch of the tire. i can see caster and king pin inclination effecting the contact patch while turning but not scrub radius. it seems to me that caster angle and kingpin inclination could change the contact patch while turning even with a zero scrub radius. i just can't picture in my head scrub radius causing the tires to ride on their edges while turning. i can see you braking point though.

Put a vehicle on corner weight scales with turn tables under the front tires. Scrub radius can effect how much weight is jacked diagonally. It will also change the wheelbase on each side.

i can see that but i can't see scrub radius causing the tires to ride on the edges during a turn.

That's wide angle distortion and the distortion is worse in different parts of the photo.

i admitted defeat on the photo. it's not wide angle distortion though, it's called perspective.

I have some published sources that agree with my Ackermann theories.

so let's get some reference to these published sources for one. and i'm sure lot's of books were written about how the earth was flat.

Off road is it considered important? Due to the outrageously high slip angles I wouldn't see how it could be, but I'm open to new ideas.

so what about when you're in a silt bed, and the entire side wall of your tire is steering? what about slow speed stuff, you aren't going 70 100% of the time?

we agree on one thing...the spelling is ackermann.

...we agree on one thing...the spelling is ackermann.And you might want to fix your shift key so you can capitalize it because it is a proper noun:p

I think this was mentioned earlier but I'm not sure everyone knows the link
http://mysite.verizon.net/triaged/files/ackermann.zip

That was posted up on the RaceTech mag's web site around 8 years ago. I don't have the article that goes with it and I didn't make the spreadsheet.

When searching the net for stuff on Ackermann ignore all the roundy-round stuff because they get it by using different length steering arms...they only turn left remember.

While we are on the subject some very good info can be found in the Chassis Newsletters by Mark Ortiz. Don't dismiss pavement info outright. The definitions are all the same and so are many of the concepts it is just the application that is a bit different because of tires working in the surface rather then on it.
http://www.2kgt.com/MarkOrtiz/

Same stuff as anti-squat (IC, CoG Height, Wheelbase), but multiplied by % front brakes. The next question is if you want to run anti-dive or pro-dive...

could you go into this in detale? i guess i get what your talking about. like negative torq cause by breaking affecting the chassey? how does one do it. giving angle to the a arms? ive never heard of this but i assume its something like that anyways/

I'm not going to play favorites here- I have to say :flipoff2::laughing:.
We can debate why it doesn't work- I'd rather we say lesson learned and forget about it. I am moving on.

my calibrated napkin works better than my calibrated eye...

Did you post the photograph and calculate suspension geometry off that? Apparently you may not know the answer, you seem to think this was aimed at you, so I guess I will have to tell you. IT WAS NOT.

well either way i was probalby one of the first people to say it was off and you tried to call me out on it... i didnt care enough to post a picture but ya i did notice it. either way you have a bad attitude.

In some of Carroll Smith's early books he stated negative Ackerman (toe-in with steering) was the way to go. In some of his later books he stated that every car that he put more Ackerman into turned better and that he had changed his mind even though the numbers didn't quite add up. Personally I have done everything from parallel steer to having the intersection 25% of the wheelbase in front of the rear axle centerline but never negative.

What does +/-/parallel Ackerman do to bump steer straight ahead and at full lock? Does anyone ever check bump steer at full lock?

FWIW I did some searching and asking around years ago about the spelling. The guy who the principal is named after was named Ackermann. Sometime it got Americanized and the 2nd "N" fell off. So now most texts call it Ackerman steering.:rolleyes: http://www.googlefight.com/index.php?lang=en_GB&word1=ackermann&word2=ackermanwell it would make sense how more ackerman would turn better... i mean more turn =more bite so ya? how much vs premature tire wear er well ya only testing would work that and one would have to put up with the wear.

[QUOTE=spork2367;8147647] "it's called scale. i can use his tire size and other angles in the photo as a scale to come up with a pretty accurate estimate. until i see a photo of a string running along both ball joints to the ground i'm not going to buy that he (frog) is even close to zero scrub radius. i'm a machinist, i do autocad 2d and autodesk inventor 3d parametric drawing...i'm pretty good. i didn't draw this up in microsoft paint."

You buying it now? Pretty good at what again?:flipoff2:
Do me a favor and examine that picture closer again. Do straight lines along the edges of the filing cabinet on the one side and something else on the left that would be considered straight up and down in real life. Notice how it angles in at the bottom? Notice how the wheels appear to be toe'd out alot? That's wide angle distortion and the distortion is worse in different parts of the photo. Telephoto lens give less distortion but have to be used at a distance and screw up depth perception. Normal cameras have these lens built in usually, if it has just one lens it will be a wide angle one. Let's call this lesson learned and move on. I have. Enough with the photo.

http://www.pirate4x4.com/forum/attachment.php?attachmentid=365128&d=1208193844

sorry for the multi quote guys...


its pretty fucking funny that even with the "lense distortion" spork was goddamn almost spot on when compared to frogs actually ruler/bar jivers... so again what the fuck are you trying to argue give it up man your wrong deal with it... he says 1.1 but the rulers clearly say around 3"... So ya?

i can see that but i can't see scrub radius causing the tires to ride on the edges during a turn.

imagine a dually dana 60 fron axle... turnign lock to lock wiht dually wheels turned out.... make sense now? your wheels when you turn them lock to lock one has negative camber the other positive... all about scrub angle. now stick your wheels out a foot or two and then imagine it... sure its not as bad when ona smaller scale but for visual purposes just imagine it on a large scale, the concept is the same reguardless of he scale so ya.

well either way i was probalby one of the first people to say it was off and you tried to call me out on it... i didnt care enough to post a picture but ya i did notice it. either way you have a bad attitude.

I'd rather have a bad attitude and be right than be a cheerful idiot:flipoff2:

well it would make sense how more ackerman would turn better... i mean more turn =more bite so ya? how much vs premature tire wear er well ya only testing would work that and one would have to put up with the wear.

Negative Ackermann is less turn in not more.

[QUOTE=piratebuggy;8150925]

sorry for the multi quote guys...


its pretty fucking funny that even with the "lense distortion" spork was goddamn almost spot on when compared to frogs actually ruler/bar jivers... so again what the fuck are you trying to argue give it up man your wrong deal with it... he says 1.1 but the rulers clearly say around 3"... So ya?

So ya? Are you familiar with the metric system? Look at the ruler again, this time at the inches side......:eek:
Who was wrong? That would be you-you need to stop posting this dribble really, you are making yourself look bad.:shaking:

i can see that but i can't see scrub radius causing the tires to ride on the edges during a turn.

imagine a dually dana 60 fron axle... turnign lock to lock wiht dually wheels turned out.... make sense now? your wheels when you turn them lock to lock one has negative camber the other positive... all about scrub angle. now stick your wheels out a foot or two and then imagine it... sure its not as bad when ona smaller scale but for visual purposes just imagine it on a large scale, the concept is the same reguardless of he scale so ya.



i really don't think think scrub radius has anything to do with camber angles. i think the angle of camber change during turning would be exactly the same with 12" of scrub radius as it would with zero. the distance traveled would be greater with a larger scrub radius but the angles would be the same, i think.

i agree with triaged that a large scrub radius will change wheelbase during turning. i also agree that because of camber and caster, a large scrub radius can cause lifting during turning (with a zero degree camber and caster it wouldn't). i don't think scrub radius causes the tires to lean during turning.

"i admitted defeat on the photo. it's not wide angle distortion though, it's called perspective."

Second helping of crow? The wide angle lens distorts perspective. Stop. Seriously.

"so let's get some reference to these published sources for one. and i'm sure lot's of books were written about how the earth was flat. "

Carroll Smith "Tune to Win" 1978 and "Engineer in your Pocket" 1998
I would like to write a book on how flat your head seems. There's one reference. I have others.

"so what about when you're in a silt bed, and the entire side wall of your tire is steering? what about slow speed stuff, you aren't going 70 100% of the time?"

Again-at slower speeds Ackermann can be useful on pavement. Like the grocery store parking lot. With grandma driving, maybe you driving I don't know.
You are saying that in silt your tires aren't constantly incurring huge slip angles?:confused:



we agree on one thing...the spelling is ackermann. I spell it Ackermann:p- it's a guy's name after all, my way of paying homage to the long gone but not forgotten.

i really don't think think scrub radius has anything to do with camber angles. i think the angle of camber change during turning would be exactly the same with 12" of scrub radius as it would with zero. the distance traveled would be greater with a larger scrub radius but the angles would be the same, i think.

i agree with triaged that a large scrub radius will change wheelbase during turning. i also agree that because of camber and caster, a large scrub radius can cause lifting during turning (with a zero degree camber and caster it wouldn't). i don't think scrub radius causes the tires to lean during turning.
turn a car lock to lock, the camber will change realitive to the car.
not just because of scrub but the combination of that with caster, it has more to do with caster but ya...

Negative Ackermann is less turn in not more.
where did i specfically say NEGATIVE ackerman.
[QUOTE=g-wizz;8151999]

So ya? Are you familiar with the metric system? Look at the ruler again, this time at the inches side......:eek:
Who was wrong? That would be you-you need to stop posting this dribble really, you are making yourself look bad.:shaking:

it could be. you cant see the two pieces of metal when he does a far away shot. and uhhh er uhhh the camera is distorting it broooo.

where did i specfically say NEGATIVE ackerman.
[QUOTE=piratebuggy;8152206]

it could be. you cant see the two pieces of metal when he does a far away shot. and uhhh er uhhh the camera is distorting it broooo.

The post you commented on was talking about negative Ackermann, you replied that "more turn equals more bite". More "turn" would be positive Ackermann.
So now you are saying he faked the camera shots? OMG dude seriously?:shaking:

Put a vehicle on corner weight scales with turn tables under the front tires. Scrub radius can effect how much weight is jacked diagonally. It will also change the wheelbase on each side.

I want to revisit this- this statement is not correct.
Since it seems like the thread has calmed down a bit I might as well stir it back up again :flipoff2:
Let's see who out there knows the correct answer- I am going to hold off giving it for a bit. Maybe there are some people lurking this thread who haven't wanted to get their heads bit off by posting their ideas but do know something about this stuff. Let's here some ideas about this.
I can prove what I know about this with a real vehicle that I own BTW. Anybody getting mouthy and personal about it better have some proof to back themselves up, anybody wanting to discuss it calmly will be dealt with respect, at least by me.
Post up! Winner gets to be hero of the thread for a week:flipoff2:

turn a car lock to lock, the camber will change realitive to the car.
not just because of scrub but the combination of that with caster, it has more to do with caster but ya...

i don't think that camber change has anything to do with scrub radius. the more i think about it, i will almost guarantee that the angle of camber change during steering would be exactly the same with a 12" scrub radius as it would be with zero scrub radius.

You are on the right track "300sniper" to answer the question of the week. Keep going.

He said scrub *can* effect weight jacking, which is true. If you want to figure it out you'll need to factor in caster, king pin inclination, and to an extent camber.

To call the statement that you said is false false you have to prove that never does scrub radius effect diagonal weight jacking. You can't do this, so the statement is in fact not incorrect. If he said *always* rather than *can* then you would have an argument.

Respectfully I disagree. I can prove that scrub radius does not affect diagonal weight jacking (i.e. ride height changes are another way of expressing this). At least you have the 'valves' to post up ;)

Respectfully I disagree. I can prove that scrub radius does not affect diagonal weight jacking (i.e. ride height changes are another way of expressing this). At least you have the 'valves' to post up ;)


if we are talking about ride height changes during turning, that would be a combination of caster, kingpin inclination and scrub radius. the scrub radius alone does not cause this. it would control the distance or amount of lift (or lowering) during turning. with caster and kingpin inclination set to zero, there would be no ride height change during turning, even with a large scrub radius. with a small amount of either caster or kingpin inclination and a large scrub radius you will start to see a ride height change during turning. with a large amount of caster or kingpin inclination and a small scrub radius you will still see ride height change during turning. with a large amount of caster or kingpin inclination and a large scrub radius you will get a lot of ride height change.

i guess what i am trying to say is that scrub radius does not cause ride height change during turning. caster and kingpin inclination do but scrub radius can increase it.

In my opinion you are on the right track but haven't got the exact answer here. Very close though. I agree that by increasing scrub radius you would be exaggerating the effect of this one angle, but it's one angle alone that is responsible for weight jacking. Let's say that you increase scrub radius by putting on a wheel spacer or a different wheel offset or something lke that. But what one angle are you exaggerating the effect of? That is the key.
Ride height changes are the poor man's way of measuring weight jacking. Scales are the only way to really tune a suspension, but the end result will be a change in ride height with a change in loading on a given corner. I don't own any scales... *looks at ground and sniffs* but I can show corner loading changes by measuring ride height changes.

a negative kingpin inclination angle would cause the front end to lift on both sides the same amount while turning either direction. a positive caster would raise the side you are turning toward and lower the other side.

i am not sure if i understand you "question" exactly but if i had to say one angle that would effect the weight in that corner it would be caster.

In my opinion you are on the right track but haven't got the exact answer here. Very close though. Let's say that you increase scrub radius by putting on a wheel spacer or a different wheel offset or something lke that. But what one angle are you exaggerating the effect of? That is the key.

besides aligning cars and reading a few books, what is your experience with building a-arm suspensions? we're getting a lot of your opinion, but i'm seeing nothing at all to back any of it up. no numbers, trig., references, sources.

when you change your wheel offset, the only thing actually changing is scrub radius. you also get more travel with less of a change in angle of the a-arms.

Respectfully I disagree. I can prove that scrub radius does not affect diagonal weight jacking (i.e. ride height changes are another way of expressing this). At least you have the 'valves' to post up ;)

Haha, then game is over and it's time you prove it. I'm not even sure you really understand weight jacking so prove that first. Then maybe I'll be willing to correct your thinking on scrub radius. If you ask a question you should really know the answer! But I leave this opening for you to prove me wrong. Respectfully, of course!

I want to revisit this- this statement is not correct...That statement was about the last one I expected to get called out on. There are all sorts of factors that would go into how much diag. weight jacking is present in turning (on corner weight scales). With the soft wheel rates and anti-roll bars (if any) on off-road race vehicles I really don't think it would matter much anyways. Go ahead and pick something else I said to tear apart:flipoff2:

It would be cool if we could have conversations on these kind of topics without you guys jerking off all over each other...

That statement was about the last one I expected to get called out on. There are all sorts of factor that would go into how much diag. weight jacking is present in turning. With the soft wheel rates anti-roll bars on off-road race vehicles I really don't think it would matter much anyways. Go ahead an pick something else I said to tear apart:flipoff2:

It is true that the sway bars would attempt to transfer the weight to the other side, maybe I should have specified unbolting sway bars. How much weight jacking is not what I'm talking about, just the actual effect thereof. As I said I don't play favorites :flipoff2:

It would be cool if we could have conversations on these kind of topics without you guys jerking off all over each other...

I had a dream...:laughing:

Haha, then game is over and it's time you prove it. I'm not even sure you really understand weight jacking so prove that first. Then maybe I'll be willing to correct your thinking on scrub radius. If you ask a question you should really know the answer! But I leave this opening for you to prove me wrong. Respectfully, of course!

Then correct me if I'm wrong, weight jacking can be thought of like the Sprint Cup cars with their adjustable screw jacks atop the springs. By turning the 'screws' they can make that corner take more or less weight of the race car. This will result in a change in ride height at that corner also.

besides aligning cars and reading a few books, what is your experience with building a-arm suspensions? we're getting a lot of your opinion, but i'm seeing nothing at all to back any of it up. no numbers, trig., references, sources.

when you change your wheel offset, the only thing actually changing is scrub radius. you also get more travel with less of a change in angle of the a-arms.

Correct, I haven't backed it up yet. Read closer next time.
You just restated what I was saying about exaggerating the effects of the angles.

You just restated what I was saying about exaggerating the effects of the angles.

you haven't really provided anything constructive...this isn't a f*cking guessing game. if you have some valid information to provide, do it. no one wants 10 "you're getting warmer" posts, they are just clogging the thread.

you present yourself as some sort of expert, but i think your knowledge ends at aligning cars.

so what angles are changed or exaggerated? (also, exaggerated means "to represent as greater" so in this case the a-arm angles would be less.) and what's your proof besides "it's my opinion."

Alrite alrite- I wanted to promote a discussion about this so I put it as a "guessing game". If someone knew the answer they wouldn't be guessing would they? Just thought this would be more fun this way.
I don't present myself as some sort of expert, most certainly not anymore than any of the other people writing here. My job currently is as an alignment specialist so I am well versed in the angles. My aim here though was to clear something up about the angles and hopefully help others understand them better. If it came off as though I was condesending I apologize, that was unintentional.
This thread IS FOR discussion of alignment angles-tell me how discussing alignment angles clogs up the thread.
The answer was actually pointed out to me some time ago on this very forum site and in the process of trying to prove him wrong I discovered that I was wrong. I thought caster was responsible for weight transfer, it is not.

The correct answer is SAI.

Here is a good reference that explains this better than I ever could.
http://beluap.tripod.com/crash5.html
Read the first section about SAI. Notice the part about "weight projection". That is the key. I found this today BTW, it is presented here as backup reference for what I already knew.
My personal proof is a series of photographs (with straight edge rulers used for reference. Yes I know you will cry about it, but once you see them it will be like looking at frog's photos he posted the last time. calm down.) that show how one vehicle (2002 Camaro Z28 with a stiff sway bar BTW) with a large SAI has a large weight transfer (ride height change) while another vehicle (old VW Beetle kingpin front end with no sway bar BTW) with a small SAI has a very small weight transfer. Both these vehicles have a substantial positive caster angles, small camber angles, scrub radius' etc. The main difference between them is their SAI angle differences.
Admittedly this is proof based on real world observation and not trig or computer programs etc., but who here could find the answer based on mathematics anyway?
Due to the fact that my digital camera got boosted recently I have snapped some film, you will have to wait until tomorrow for the pics.
Feel free to post any and all comments, questions, hysteria, etc.

Alrite alrite- I wanted to promote a discussion about this so I put it as a "guessing game". If someone knew the answer they wouldn't be guessing would they? Just thought this would be more fun this way.
I don't present myself as some sort of expert, most certainly not anymore than any of the other people writing here. My job currently is as an alignment specialist so I am well versed in the angles. My aim here though was to clear something up about the angles and hopefully help others understand them better. If it came off as though I was condesending I apologize, that was unintentional.
This thread IS FOR discussion of alignment angles-tell me how discussing alignment angles clogs up the thread.
The answer was actually pointed out to me some time ago on this very forum site and in the process of trying to prove him wrong I discovered that I was wrong. I thought caster was responsible for weight transfer, it is not.

The correct answer is SAI.

Here is a good reference that explains this better than I ever could.
http://beluap.tripod.com/crash5.html
Read the first section about SAI. Notice the part about "weight projection". That is the key. I found this today BTW, it is presented here as backup reference for what I already knew.
My personal proof is a series of photographs (with straight edge rulers used for reference. Yes I know you will cry about it, but once you see them it will be like looking at frog's photos he posted the last time. calm down.) that show how one vehicle (2002 Camaro Z28 with a stiff sway bar BTW) with a large SAI has a large weight transfer (ride height change) while another vehicle (old VW Beetle kingpin front end with no sway bar BTW) with a small SAI has a very small weight transfer. Both these vehicles have a substantial positive caster angles, small camber angles, scrub radius' etc. The main difference between them is their SAI angle differences.
Admittedly this is proof based on real world observation and not trig or computer programs etc., but who here could find the answer based on mathematics anyway?
Due to the fact that my digital camera got boosted recently I have snapped some film, you will have to wait until tomorrow for the pics.
Feel free to post any and all comments, questions, hysteria, etc.

i still think that if the caster is zero, a negative kingpin inclination (i guess the correct term is sai) will lift both side equally while steering. i don't see how that can cause weight transfer, well maybe a slight amount because of wheelbase change from side to side. now a caster angle will cause one side to lift and the other to lower. this would definatly cause a weight transfer. i have absolutely no background in this so i really want to understand if i am wrong.

...I wanted to promote a discussion about this so I put it as a "guessing game".I'm not a big fan of guessing games. I try to ask questions to provoke thought and lead people to consider things differently then they normally would. I do that mostly because I can't/shouldn't be divulging that kind of info. It is a fine line but I try not to play games and I hope I don't come off that way:D

The correct answer is SAIThat might be part of the correct answer but in reality everything down to the stiffness and squareness of the tires will come into effect.

...Admittedly this is proof based on real world observation and not trig or computer programs etc., but who here could find the answer based on mathematics anyway?I think you would be surprised by how many people here could (most of them I'm sure would be engineers). I'm sure I could but I don't see a reason to. FWIW Susprog3D includes this as part of the steering calculations as Jacking effect which it defines as "the amount that the bottom ball joint rises and falls as the wheel is turned". The free trial version will let you do everything other then change the tire size and wheelbase and the full version only costs about $200. http://www.susprog.com/

I designed a car (just the suspension and steering) with 0° SAI (spindle axis perpendicular to steering axis), 7-8° of caster, and about 2-1/8" of scrub radius. While I never measured the actual having the steering not centered would sure make a HUGE difference in the corner weights of the car. No it wasn't easy to turn...and the added aero-downforce didn't help:flipoff2: Attached is a pic with my ugly mug far right and front.:grinpimp:

If you reread my response you will see that I also have a vehicle that has a very small SAI but a substantial positive caster angle. It's weight jacking amount is barely perceptible. The other vehicle has a large SAI , around 5* positive caster (substantial), and has a very perceptible diagonal weight jacking effect. Neither vehicle has very much camber. Logical conclusion would point to SAI being the difference.
If you reread the link I posted you will notice how they define what each angle does.

SAI works WITHIN the point of road contact exclusively.
Caster works OUTSIDE the point of road contact exclusively.
I think that may be the key.
As I stated I used to think about this the wrong way, I believe this to be correct now.

This thread IS FOR discussion of alignment angles-tell me how discussing alignment angles clogs up the thread.
The answer was actually pointed out to me some time ago on this very forum site and in the process of trying to prove him wrong I discovered that I was wrong. I thought caster was responsible for weight transfer, it is not.


the alignment angle stuff isn't clogging the thread, the "you're getting warmer" bullshit was.

where does the part about the wheel spacers you mentioned earlier play into what you just posted? where does the part of exaggerated angles that you mentioned play into this. you post some question, then your answer doesn't seem to coincide with the original issue.

all that SAI part of that site describes is king pin inclination and scrub radius...nothing new. and caster is the primary factor concerning your tire tracking straight and your steering wheel recentering, not king pin inclination (SAI) which he states.

If you reread my response you will see that I also have a vehicle that has a very small SAI but a substantial positive caster angle. It's weight jacking amount is barely perceptible.It also had no anti-roll bar and (if stock size) tires of a larger aspect ratio. You seem to be focusing on one thing to cause this when there are dozens. The other vehicle has a large SAI , around 5* positive caster (substantial), and has a very perceptible diagonal weight jacking effect. Neither vehicle has very much camber.

Logical conclusion would point to SAI being the difference.Not the conclusion I come to. You can't directly compare something with more then 1 change. In this case you compared 50 years of changes. This would be down on my list of design criteria at about 184th. Even if it works the way you say (which I am not close to being convinced of) I will still choose to ignore it when applied to long travel suspension off-road race vehicles.

Something more relevant to discuss would be how SAI and caster affect camber with steering.


To get this thread back on a track that it was never on in the first place...

Here is a link from Race-Dezert that matches the topics here:
http://race-dezert.com/forum/showthread.php?t=22077

the alignment angle stuff isn't clogging the thread, the "you're getting warmer" bullshit was.

where does the part about the wheel spacers you mentioned earlier play into what you just posted? where does the part of exaggerated angles that you mentioned play into this. you post some question, then your answer doesn't seem to coincide with the original issue.

all that SAI part of that site describes is king pin inclination and scrub radius...nothing new. and caster is the primary factor concerning your tire tracking straight and your steering wheel recentering, not king pin inclination (SAI) which he states.

1. That was one post -get a life -move on:shaking:
2. Wheel spacers was something the other guy brought up. It seems logical that they would exaggerate the effects of SAI. I haven't tested this myself I don't know. The original issue was the weight jacking effects of alignments angles, the answer fits that.
3. Reread again *whew* Notice the part about "weight projection"?
SAI is a directional control angle.

Thank you for more hysteria.:shaking:

It also had no anti-roll bar and (if stock size) tires of a larger aspect ratio. You seem to be focusing on one thing to cause this when there are dozens. The other vehicle has a large SAI , around 5* positive caster (substantial), and has a very perceptible diagonal weight jacking effect. Neither vehicle has very much camber.

Not the conclusion I come to. You can't directly compare something with more then 1 change. In this case you compared 50 years of changes. This would be down on my list of design criteria at about 184th. Even if it works the way you say (which I am not close to being convinced of) I will still choose to ignore it when applied to long travel suspension off-road race vehicles.

Something more relevant to discuss would be how SAI and caster affect camber with steering.


To get this thread back on a track that it was never on in the first place...

Here is a link from Race-Dezert that matches the topics here:
http://race-dezert.com/forum/showthread.php?t=22077

1. No sway bar would mean it is able to weight jack one corner easier on the vehicle with the minimal weight jacking occuring. The vehicles alignment angles are similar except for the SAI. You are saying now that you will ignore SAI? ok?
2. You will always be able to discuss something else if you like.
We were discussing aligment angles in general, apply the generalities to whatever specifics fit the vehicle in question. Don't overcomplicate this. Yes the effects of the angles will be influenced by the variables of various vehicles, but the effects are still there. Knowing it will help with the design of suspensions.

I don't ignore SAI/KPI. What I ignore is any little effect it might have on weight jacking in a static turn. Stiffer roll rates will cause more weight jacking. I am not wrong on that. I don't think ignoring something over-complicates it.

1. That was one post -get a life -move on:shaking:
2. Wheel spacers was something the other guy brought up. It seems logical that they would exaggerate the effects of SAI. I haven't tested this myself I don't know. The original issue was the weight jacking effects of alignments angles, the answer fits that.
3. Reread again *whew* Notice the part about "weight projection"?
SAI is a directional control angle.

i don't know what your referring to when you say one post, there were a few.

you commented on the wheel spacer issue as part of your argument then mentioned nothing about it. i was just wondering where you thought that played in. if you "don't know" then why ask it as a question like you knew the answer?

"SAI provides good driving and handling characteristics through directional stability and weight projection."

"Weight projection is the projection of the vehicle's weight to a point within the road contact area of the tire. The weight projection point at the road surface is the point where the wheel pivots for turning. SAI is determined by a true plumb line, placed at the center of the wheel at the point of road contact, and the projected line created by the strut or the upper and lower ball joints."

these are the only two comments out of that link that talk about weight projection, and all they do is mention it in reference to king pin inclination and scrub radius. nothing in there actually mentions weight shifting or any dynamic weight transfer. so you haven't proven anything. all that article states is that your tire turns about the point formed by the scrub radius (no shit), and your king pin inclination helps control stability and tracking (again, no one here is arguing against this). neither of those are new things.

Not the conclusion I come to. You can't directly compare something with more then 1 change. In this case you compared 50 years of changes. This would be down on my list of design criteria at about 184th. Even if it works the way you say (which I am not close to being convinced of) I will still choose to ignore it when applied to long travel suspension off-road race vehicles.

i completely agree with this. you can't look at an entire suspension setup and say "this is the only important issue." it's all important. including scrub radius and ackermann. some is more important, and some not very at all. piratebuggy has failed to even stay on his own track. the link he provided failed to talk about weight transfer at all.

1. No sway bar would mean it is able to weight jack one corner easier on the vehicle with the minimal weight jacking occuring.

2. We were discussing aligment angles in general, apply the generalities to whatever specifics fit the vehicle in question. Don't overcomplicate this. Yes the effects of the angles will be influenced by the variables of various vehicles, but the effects are still there. Knowing it will help with the design of suspensions.

1. that sentence doesn't even make sense. and the sway bar really just reduces body roll which transfers weight onto the outside, and more specifically outside front tire. a sway bar increases spring rate because it is forcing the spring on the other side to compress.

2. you have yet to actually discuss what effect any of this has on angles. you posted up a link that explains the basics we've already established, and some example that none of us have seen. spectacular... then you start talking about sway bars. so, i must be stupid. please rehash the posts where you actually stated what effect various suspension angle changes have on suspension characteristics.

There seems to be alot of confusion regarding what effect the various angles do. Let's go for a simple explanation here of caster and it's effect on weight jacking and camber changes for example. Go to the supermarket. Get a grocery cart. Look down at the wheels, those are "caster' wheels so named for their caster setting. Spin wheels around in a circle. Notice any weight jacking? Camber changes? That is a simple illustration of pure caster without any other angles to confuse yourself with. By separating the angles it should becomes easier to see what each one does. Of course combining caster with SAI will result in differences that either one angle alone would produce.
I'm not here to teach a class. "spork" needs to stop challenging everything I say like it's a contest or a class. "Spork" hasn't contributed anything of value to any thread I've seen to date.

I don't ignore SAI/KPI. What I ignore is any little effect it might have on weight jacking in a static turn. Stiffer roll rates will cause more weight jacking. I am not wrong on that. I don't think ignoring something over-complicates it.

Ok let's site another reference that agrees with me....
http://www.familycar.com/Alignment.htm#Steering%20Axis%20Inclination%20(SAI )
"This angle, when added to the camber to form the included angle (see below) causes the vehicle to lift slightly when you turn the wheel away from a straight ahead position. This action uses the weight of the vehicle to cause the steering wheel to return to the center when you let go of it after making a turn."
Notice where it says it uses the weight of the vehicle < aka weight jacking>< aka weight projection >?
They confuse the issue alittle with the included angle reference, even with zero camber the weight transfer still holds true.
Shall I continue searching references that agree with what I am trying to say?

http://www.procarcare.com/icarumba/resourcecenter/encyclopedia/icar_resourcecenter_encyclopedia_suspsteer3.asp#ge ometry
See figure 18, notice last sentence of the section on SAI?
That's 3 separate references, want more?

...causes the vehicle to lift slightly when you turn the wheel away from a straight ahead position. This action uses the weight of the vehicle to cause the steering wheel to return to the center when you let go of it after making a turn...Lifting the front end does not cause weight jacking! What does is lifting one front wheel more then the other.

Shall I continue searching references that agree with what I am trying to say?That one doesn't agree with you and there is no need for more.

http://www.rqriley.com/images/fig-6.gif
see figure 6 section about halfway down the page
I can highlite the important part here

"Steering axis inclination is responsible for most of the self-centering force of the steering system. The steering axis of passengers cars normally leans inboard 10 to 15 degrees. The incline places the swivel-line the wheels off-plane with the ground. As a result, a steering movement in either direction moves the wheels downward and lifts the vehicle upward. The weight of the vehicle therefore produces a resultant that keeps wheels aligned to the vehicle heading. "
http://www.rqriley.com/suspensn.htm

Lifting the front end does not cause weight jacking! What does is lifting one front wheel more then the other.

That one doesn't agree with you and there is no need for more.

Lifting one corner IS the definition of diagonal weight jacking-which is what the entire discussion was about. SAI lifts one wheel while dropping the other side. I realize these references aren't clear if you don't understand the subject matter well.
I'm thinking alot of people over indulged in the 420 celebrations:eek:

There seems to be alot of confusion regarding what effect the various angles do. Let's go for a simple explanation here of caster and it's effect on weight jacking and camber changes for example. Go to the supermarket. Get a grocery cart. Look down at the wheels, those are "caster' wheels so named for their caster setting. Spin wheels around in a circle. Notice any weight jacking? Camber changes? That is a simple illustration of pure caster without any other angles to confuse yourself with. By separating the angles it should becomes easier to see what each one does. Of course combining caster with SAI will result in differences that either one angle alone would produce.
I'm not here to teach a class. "spork" needs to stop challenging everything I say like it's a contest or a class. "Spork" hasn't contributed anything of value to any thread I've seen to date.

there isn't anything to challenge, you really haven't provided any information. i'm not well versed on dynamic weight transfers due to various suspension geometry, so i'd like to learn that too, but you haven't really posted more than a sentence or two in all your posts that has actually tried to explain anything. i understand the definition of caster, camber, and all that other jazz, and i understand their basic effects while driving. what i think this discussion is trying to accomplish is explaining how a change in one effects another. and that's great, that's what i'd like to learn too. i'm not here to contribute a lot, i'd like to leave that to the experts. i just know enough to be dangerous. i'm here to learn. but you aren't helping.

Ok let's site another reference that agrees with me....

"This angle, when added to the camber to form the included angle (see below) causes the vehicle to lift slightly when you turn the wheel away from a straight ahead position. This action uses the weight of the vehicle to cause the steering wheel to return to the center when you let go of it after making a turn."
Notice where it says it uses the weight of the vehicle < aka weight jacking>< aka weight projection >?
They confuse the issue alittle with the included angle reference, even with zero camber the weight transfer still holds true.
Shall I continue searching references that agree with what I am trying to say?


spell it out for us stupid people. what exactly are you saying is occurring with weight transfer, and what aspects of the geometry are you saying affect that?

The weight of the vehicle therefore produces a resultant that keeps wheels aligned to the vehicle heading.

there is no weight jacking on a shopping cart. the wheel doesn't lift at all when spun around. so how does it track the right direction when pushing the cart....it's called caster....and it is the primary reason your steering wants to return to zero, not weight jacking.

also, sway bars are to control a completely different type of weight transfer, the weight transfer from body roll. that has to do with the COG of the car, and lateral gravitational forces.

Lifting one corner IS the definition of diagonal weight jacking-which is what the entire discussion was about. SAI lifts one wheel while dropping the other side...Really? SAI tends to lift the front end as a whole just like the links you sighted say. Caster combined with scrub radius tend to jack weight.

there is no weight jacking on a shopping cart. the wheel doesn't lift at all when spun around. so how does it track the right direction when pushing the cart....it's called caster....and it is the primary reason your steering wants to return to zero, not weight jacking.This doesn't help..."casters" don't have any caster. Just a bunch of mechanical trail.

This doesn't help..."casters" don't have any caster. Just a bunch of mechanical trail.

umm. they have negative caster...the angle between the pivot where they are mounted and the center of the axle. whether negative or positive caster provides stability is based on whether the vehicle is front wheel, rear wheel, or all wheel drive.

i would call this caster, but i've been wrong before. (or maybe it's actually straight up and down and it's just wide angle distortion:flipoff2:)

1. Ok I made an incomplete statement there earlier. What I was trying to say was that SAI when combined with caster diagonally weight jacks. The point I was trying to make all along was that SAI is responsible for the weight jacking, not caster or whatever.
2. I suppose some would try to express SAI as a function of scrub radius? We may be nitpicking terms here...
3. Supermarket casters most certainly do have caster, the end result is trail.
I see wide angle distortion hahaha......spork does have a sense of humor after all!

there is no weight jacking on a shopping cart. the wheel doesn't lift at all when spun around. so how does it track the right direction when pushing the cart....it's called caster....and it is the primary reason your steering wants to return to zero, not weight jacking.

also, sway bars are to control a completely different type of weight transfer, the weight transfer from body roll. that has to do with the COG of the car, and lateral gravitational forces.

1. Correct- the caster has no weight jacking effects, my point exactly.
2. My point about the sway bars may be a bit off, my point was to show that the sway bar equipped vehicle has the most weight transfer, the other has no sway bar and minimal weight transfer. Maybe that's because they have no effect on diagonal weight transfer, I was under the impression they did but it may be only a side to side effect instead.
We're all here to learn and I am no different. I have learned stuff from this thread and others in the past few weeks.

Wow. Both of you go back and read what I have said. I am not wrong. If you think I am start another thread or send me a PM. Reading some introductory text on vehicle dynamics would help loads. We don't need 3 pages of this.

Dan,
Give up now. I'm the worst at not giving up on folks, but this is bad. Let them hash everything out with their 'intuition'. They'll have fun for ages. Also, that race-desert thread is good til the 3rd and 4th page. It makes me smile when I see how they think body roll IS weight transfer and more weight transfer means more traction. Dump is terrible at spreading this. This is 'intuition' calculation at it worst! Also, check the IC thread. I posed a couple question to you I'd like to see you answer. :D

Piratebuggy,
Read the first post I produced. It is 100% correct. Kingpin inclination is the same thing as your magic angle SAI. I know you think you've found the holy grail, so enjoy it!!! It's just another angle that means almost nil all by itself. I understand what you're attempting to say, but you're still missing the big picture.

i would call this caster, but i've been wrong before. (or maybe it's actually straight up and down and it's just wide angle distortion:flipoff2:)

Yes, you are wrong. Apply the definition of caster to that wheel and see what happens. That is NOT caster.

...Also, check the IC thread. I posed a couple question to you I'd like to see you answer. :DOh...I saw it:flipoff2:

It makes me smile when I see how they think body roll IS weight transfer...

Piratebuggy,
Read the first post I produced. It is 100% correct. Kingpin inclination is the same thing as your magic angle SAI. I know you think you've found the holy grail, so enjoy it!!! It's just another angle that means almost nil all by itself. I understand what you're attempting to say, but you're still missing the big picture.

those are both things that i said earlier...that sway bars and body roll are not weight transfer and are separate from the suspension geometry. i also said about that article on SAI being a basic article on king pin inclination and scrub radius.

those are both things that i said earlier...that sway bars and body roll are not weight transfer and are separate from the suspension geometry. i also said about that article on SAI being a basic article on king pin inclination and scrub radius.

Unless you posted in that race-dezert thread from '06 I wasn't talking to you with that post.

Oh...I saw it:flipoff2:
Then nevermind.

Kingpin inclination is the same thing as your magic angle SAI. I know you think you've found the holy grail, so enjoy it!!! It's just another angle that means almost nil all by itself. I understand what you're attempting to say, but you're still missing the big picture.
SAI is the same thing as KPI=different name. I believe I pointed that out before.
I believe you can separate the angles and examine what each does independently of the others.
I stand by what I said-scrub radius by itself does not weight jack.
I am done posting about this-I have been told we cannot post here anymore. Sorry for one more post.

He said scrub *can* effect weight jacking, which is true. If you want to figure it out you'll need to factor in caster, king pin inclination, and to an extent camber.

To call the statement that you said is false false you have to prove that never does scrub radius effect diagonal weight jacking. You can't do this, so the statement is in fact not incorrect. If he said *always* rather than *can* then you would have an argument.

Read my post above. You basically claimed scrub radius doesn't effect weight jacking. Now you're changing that. My above answer is 100% on. Learn to understand 'can', 'must', 'always', and 'may'.

In my opinion you are on the right track but haven't got the exact answer here. Very close though. I agree that by increasing scrub radius you would be exaggerating the effect of this one angle, but it's one angle alone that is responsible for weight jacking. Let's say that you increase scrub radius by putting on a wheel spacer or a different wheel offset or something like that. But what one angle are you exaggerating the effect of? That is the key.
.

I was referring to SAI/KPI as that angle- I am sticking with it.
What we have here is failure to communicate. Got to get your mind right Luke....
:p

I don't even know what you guys are arguing about any more.

From the original page about roll centers, starting out in my early days and suspension builds I used to think they were important but that's gone the way of the dodo. About the only use for them is to keep them somewhat the same height front to rear so the vehicle doesn't jack in cornering. Far more important in handling is balancing the roll moments to get your desired effect. Roll center are used to find the R.M. and that about all I use R.C. for anymore.

As for Akerman I've found on the dirt at high speeds proper akerman doesn't do much for you. With the soft spring rates there is little to no force on the inside wheel so it's sort pointless to try to provide proper steering geometry there. It can effect you at slow speed though. We run parallel in out dirt buggies.

not sure if that's an new info or not as there was alot of crap in this thread. I'm not a whiz bang expert at V.D. either but enjoy learning about the stuff.

Really? SAI tends to lift the front end as a whole just like the links you sighted say. Caster combined with scrub radius tend to jack weight.



this is what i agree with.

There seems to be alot of confusion regarding what effect the various angles do. Let's go for a simple explanation here of caster and it's effect on weight jacking and camber changes for example. Go to the supermarket. Get a grocery cart. Look down at the wheels, those are "caster' wheels so named for their caster setting. Spin wheels around in a circle. Notice any weight jacking? Camber changes? That is a simple illustration of pure caster without any other angles to confuse yourself with. By separating the angles it should becomes easier to see what each one does. Of course combining caster with SAI will result in differences that either one angle alone would produce.
I'm not here to teach a class. "spork" needs to stop challenging everything I say like it's a contest or a class. "Spork" hasn't contributed anything of value to any thread I've seen to date.

uh caster wheels (dont) have a caster angle. maby ALOT of rake.. but no caster angle.

great example of a bad scrub radius tho...

Really? SAI tends to lift the front end as a whole just like the links you sighted say. Caster combined with scrub radius tend to jack weight.

This doesn't help..."casters" don't have any caster. Just a bunch of mechanical trail.

well you beat me to that.

"The best way to visualize caster is to picture a shopping cart caster. The pivot of this type of caster, while not at an angle, intersects the ground ahead of the wheel contact patch. When the wheel is behind the pivot at the point where it contacts the ground, it is in positive caster. Picture yourself trying to push the cart and keep the wheel ahead of the pivot. The wheel will continually try to turn from straight ahead. That is what happens when a car has the caster set too far negative. Like camber, on many front-wheel-drive vehicles, caster is not adjustable. If the caster is out on these cars, it indicates that something is worn or bent, possibly from an accident, and must be repaired or replaced."

http://www.familycar.com/Alignment.htm#Steering%20Axis%20Inclination%20(SAI )
Yes I am familiar with mechanical trail- it's just a good way to visualize the effects of caster.

"The best way to visualize caster is to picture a shopping cart caster. The pivot of this type of caster, while not at an angle, intersects the ground ahead of the wheel contact patch. When the wheel is behind the pivot at the point where it contacts the ground, it is in positive caster. Picture yourself trying to push the cart and keep the wheel ahead of the pivot. The wheel will continually try to turn from straight ahead. That is what happens when a car has the caster set too far negative. Like camber, on many front-wheel-drive vehicles, caster is not adjustable. If the caster is out on these cars, it indicates that something is worn or bent, possibly from an accident, and must be repaired or replaced."

http://www.familycar.com/Alignment.htm#Steering%20Axis%20Inclination%20(SAI )
Yes I am familiar with mechanical trail- it's just a good way to visualize the effects of caster.
some how i dont think a car with ALOT of positive caster would track very well. i thought camber was adjustable on many front wheel drive cars.. lower controll arm in/out with a cam bolt. and maby offset strut plates if they exist for caster.

what do you guys think about caster gain at bump. My old and new arms gain almost 4deg of caster from ride height to bump, and lose around 3deg from ride height to droop. I've heard to set it at say 8 deg and leave it throughout the travel and have heard to make it gain so it'll track straighter when compressed. Any thoughts on that.

ok here's my question, measure anti squat on the front, it it just the angle of the arm plane from the frame? And what usefulness is it? Besides anti-dive under braking. I suppose you could get some odd handling behavior if the rear doesn't follow the same path, jacking?

some how i dont think a car with ALOT of positive caster would track very well. i thought camber was adjustable on many front wheel drive cars.. lower controll arm in/out with a cam bolt. and maby offset strut plates if they exist for caster.

There is alot of vehicles out today with no adjustments except toe at the front end. The aftermarket supplies solutions to some of the non-adjustable camber vehicles in the form of cam bolts, but at the spindle not the lower control arm. Caster is harder to adjust very much on a strut front end vehicle due to the length of the strut and the small amount of space to move the top of the strut, if it is possible at all. Many of today's cars give more adjustments from the factory at the rear axle than at the front.
Caster gives directional stability but too much can be a bad thing. There are other angles that can give the directional stability too.

The main point (IMO) of caster change is anti-dive. I can't however recall seeing a vehicle that looked like it had greater then 0% anti-dive. I tend to lump everything into one of 3 different combinations.
1) Arms flat. No caster change and no anti/pro-dive
2) Arms raked and no caster change ending up with pro-dive.
3) Arms raked different angles and/or splayed. For the most part doing stuff with the upper arm to get rid of the pro-dive or for other reasons.

When you start doing crazy stuff with the arms calculating the anti/pro-dive and change with travel can be a pain. No I haven't written a spreadsheet to calculate that yet:flipoff2: For that you might want to look into this FAQ
http://www.eng-tips.com/faqs.cfm?fid=768

There is alot of vehicles out today with no adjustments except toe at the front end. The aftermarket supplies solutions to some of the non-adjustable camber vehicles in the form of cam bolts, but at the spindle not the lower control arm. Caster is harder to adjust very much on a strut front end vehicle due to the length of the strut and the small amount of space to move the top of the strut, if it is possible at all. Many of today's cars give more adjustments from the factory at the rear axle than at the front.
Caster gives directional stability but too much can be a bad thing. There are other angles that can give the directional stability too.

uh why did you quote me? besids the cam bolt stuff... that and how do cam bolts work on spindles?

what do you guys think about caster gain at bump. My old and new arms gain almost 4deg of caster from ride height to bump, and lose around 3deg from ride height to droop. I've heard to set it at say 8 deg and leave it throughout the travel and have heard to make it gain so it'll track straighter when compressed. Any thoughts on that.

well reguardless you dont have to many options since its a radius arm right? i guess the longer the arm the less the change. i dunno i dont see how you can design that caster change into a suspension for it to intentionally do do something at full bump when its forced to do that change at full bump.. unless you calculated your radius arms to change that much during the range of yoru suspension travel?

i dunno i would think i would want a car to track strait when the least ammount of weight was on the ground/airbone so full droop. i dunno? i dont know shit tho.:confused:

There is alot of vehicles out today with no adjustments except toe at the front end. The aftermarket supplies solutions to some of the non-adjustable camber vehicles in the form of cam bolts, but at the spindle not the lower control arm.

i'm sure being an alignment specialist you have me here, but the last new vehicle i had that needed the slots punched out, and cam bolts installed, the cam bolts came from the vehicle manufacturer, not the after market. they make the assembly line at the plant to control camber without aligning the car to save time. all the front suspensions i have seen that didn't come from the factory with adjustable camber, were still made to be adjustable with a few extra parts. any car that has struts needs adjustable camber. technically a lot of trucks with a-arms wouldn't need adjustable camber except in the case of accidents or extremely rough driving. the only vehicles i have seen that didn't have the capability of camber adjustments were solid axle.

Actually the main reason for loss of camber is spring sag, ruins the ride height and the alignment.
Every place I've worked at has used stuff from places like this- http://www.northstarmfg.com/
This is the same as the Hunter line of stuff.
GM used to have alot of struts that could have the slots ground out, but by the time the owner got around to getting an alignment it was time for a new set of struts anyway. Normally your replacement struts have slotted holes already.
On a brighter note, my company bought a new alignment rack for me to use! It's been years....they just got finished installing it yesterday.

Actually the main reason for loss of camber is spring sag, ruins the ride height and the alignment.
Every place I've worked at has used stuff from places like this- http://www.northstarmfg.com/
This is the same as the Hunter line of stuff.
GM used to have alot of struts that could have the slots ground out, but by the time the owner got around to getting an alignment it was time for a new set of struts anyway. Normally your replacement struts have slotted holes already.
On a brighter note, my company bought a new alignment rack for me to use! It's been years....they just got finished installing it yesterday.

but its good to engineer a change in camber for the travel in suspension= the ammount of sag due to the springs right?... cause keeping that camber change to a minimum is a BAD thing.

well reguardless you dont have to many options since its a radius arm right? i guess the longer the arm the less the change. i dunno i dont see how you can design that caster change into a suspension for it to intentionally do do something at full bump when its forced to do that change at full bump.. unless you calculated your radius arms to change that much during the range of yoru suspension travel?

i dunno i would think i would want a car to track strait when the least ammount of weight was on the ground/airbone so full droop. i dunno? i dont know shit tho.:confused:

my trucks are all a-armed no beamed, and I have raked the upper arm about 3deg different than the lowers and it's worked for me but wanted to see what everyone else says about it.

my trucks are all a-armed no beamed, and I have raked the upper arm about 3deg different than the lowers and it's worked for me but wanted to see what everyone else says about it.Have any pictures? Can you describe how it handles bumps coasting vs under braking?

my trucks are all a-armed no beamed, and I have raked the upper arm about 3deg different than the lowers and it's worked for me but wanted to see what everyone else says about it.

quick quiestion? when you rake the arms. is it built into the chassey or is it adjustable?
post some pics by the way. actually dont i totally mixed you up with somone else and a different build. nice toy

I'ld kinda like to steer the discussion more towards physical application of your expertise. Maybe through the use of a hypothetical situation? Lets say you have a new axle. You shave off the mounts and begin designing the radius arm system. You plan on reusing the tires that are still on your old axle that is still under your vehicle. So you know what the vehicle has now in terms of kingpin angle, caster, camber, ride height, etc. You know what the vehicle likes. But its a short arm solid axle with coil sprung suspension. You're wanting to lengthen the arms considerably with a radius arm setup. If you keep caster, camber, kpa the same as what you started with (shims, offset ball joints, wheel spacers, etc) then what's changing, why, and what's bad or good about the change or not change?

You guys have gotten into a higher level argument about what is better when near the beginning of the thread it was stated that much is personal preference about which researcher you believe in or misunderstandings through definition of terms. I hope you are having fun and I'ld like to thank you for the arguments: it's given good information and citations to accessible dissertations/research. So please keep patient and understanding. And keep sharing!
Thanks!
James