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Upper length Vs. lower length.

Jaffer said:
OK, no one mentioned this basic point ...
It's generally a good idea with a CV set up to keep the rear's upper links shorter than it's lowers so the pinion's yoke will stay pointing towards the TC's yoke.

I believe that number to be ~70% of lower link length.
 

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Booger Weldz said:

1. i dont know i sold the truck
7. any weekend you get your sand covered ass up here:flipoff2:
8. no, i use a glass pipe:D
:flipoff2: YOU SOLD THE TRUCK?
oh well it looked cool.
i just got the f350 leaves from a bud for free:D
i have steel pipe, glass breaks and burns my lippies
yes i have much sand, but i am currently loosing 100lbs (a wife) so travel should be easier.
the worst problem is that she is taking the kid and the rover with her:( at least she is only moving a few blocks away and we are still.........friends:confused: .......
 

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Jaffer said:
OK, no one mentioned this basic point ...
It's generally a good idea with a CV set up to keep the rear's upper links shorter than it's lowers so the pinion's yoke will stay pointing towards the TC's yoke.
don't think this is true the shorter the upper links in comparison the lower links the more the pinion will point toward the ground during drop out.
 

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Air Ride beat me to it. Draw out your radius's from your frame mounts and look at what it does to your pinion angle. If you keep them the same, the pinion will always point at the tc. Shorter lowers will rotate it up and help to keep you from having to buy a long travel / high misalignment d-shaft. The local guys around here that race jeeps keep telling me that 5* of pinion rotation is the max acceptable to them.
 

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The reason why the uppers should be shorter than the lowers is so that as the rear axle mover away from the frame the links the anti squat will become less.

So that if you start to climb with a certain amount of anti squat which will cause the rear axle to move away from the frame this movement will then reduce the anti squat value which lessons the tendency for the axle to keep moving away. This results in a more stable setup which will hop less on the steep climbs. It actually lets you run more anti squat at ride height so that you can get a good horizontal launch while still remaining stable on the steep climbs because the anti squat value will lesson all by itself.

If the links are all the same length as the axle moves away from the chassis the anti squat will increase which will cause the axle to move away more and the only way it can stabalise is by the extension on the rear springs (meaning the rear springs will extend more than if you ran short upper links).

I wouldnt be too concerned with the pinion angle changing - thats what uni joints are for. Probably should run a loose centre limiting strap to stop the rear from totally dropping out anyway.

Sam
 

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ErikB said:
- try to make your links parallel when veiwed from the side
I think what I should have said was "try to make them parallel with the ground," which is the same as making them "as flat as possible," so it was redundant. :rasta:


As far as making them parallel w/ each other as viewed from the side, all I can find is "its not the best way," but no solid info as to why. It "will" work, but its just "not the best way."
Yeah, yeah, the infinite IC is too far in front of the vehicle, etc., but that doesn't tell me much in terms of that actually DOES, how it affects handling...

As far as I can tell though, making them parallel to each other or not isn't nearly as important a factor to worry about as most of the other things...
 

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good thread guys. perhaps some one should explain what roll center, anti squat, instant center, etc mean and/or what part they play in layman's terms. i know that getting these down was/is the hardest part.
 

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Discussion Starter #28
chrisjeep you just said exactly what I was thinking. This thread is definitely going the direction I hoped, but I think some people are still wondering what instant center, roll center, etc, are.

Cruiserrg, you fawkin kick ass. Thats exactly the kind of post I was looking for. I think just about anyone on this board could understand almost all of that, which is exactly what I was looking for. Thanks a lot guys, you're helping a bunch of people right now, including me :D

Dallas
 

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Discussion Starter #29
Strange Rover said:
The reason why the uppers should be shorter than the lowers is so that as the rear axle mover away from the frame the links the anti squat will become less.

So that if you start to climb with a certain amount of anti squat which will cause the rear axle to move away from the frame this movement will then reduce the anti squat value which lessons the tendency for the axle to keep moving away. This results in a more stable setup which will hop less on the steep climbs. It actually lets you run more anti squat at ride height so that you can get a good horizontal launch while still remaining stable on the steep climbs because the anti squat value will lesson all by itself.



Sam
Now here is some good tech. To expand on this do you have any reccomendations on how much shorter the uppers should be? say you have 40" lower links, how long should your uppers be to achieve the right kind of S/AS curve? or maybe we should just put it down as a percentage of length.

also it was mentioned that the vertical separation at the frame should be smaller than at the axle. what effect does this have on handling? cruiserrg mentioned that you could tune your IC and AS by adjusting the separation at the frame, i guess a good explanation of IC would help me understand this a lot.

I understand the motion behind squat and antisquat, but not entirely sure how to tune it, so maybe some details on what effects antisquat would be good. thanks again guys.

Dallas
 

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Awesome thread guys! Keep it up!!

Planning on coils F&R and im just now starting to look into it... Long ways to go!!

Are there some good books for this that arent based on racing applications?

Dave
 

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TRD said:
if you really don't want to figure all the stuff out you should just copy somone elses design that works.

There was some talk a while back about a 4 link database. I'd like to see a simple list, of the pertinent measurements of people's suspension, and a few pics. Would not be hard to manage.
 

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Here is what I have written down somewhere, not sure where I got it, but I thougth it to be correct enought to keep the notes...


Make the upper links 75% length of the bottom links

Make the vertical seperation at the xfer case mount 75% of the vertical seperation at the axle

Rules of thumb.
 

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Chrisjeep7 said:
good thread guys. perhaps some one should explain what roll center, anti squat, instant center, etc mean and/or what part they play in layman's terms. i know that getting these down was/is the hardest part.
Ill have a go. A lot of these concepts and terms are fairly difficult to explain.

The roll centre is the point that the body wants to rotate about on the axle or the point that the axle supports the body laterally (or supports the body in a sideways direction). The simplest example is a triangulated 3 link with the upper links triangulated to a single point on top of the axle. This point is the roll centre. If you are talking about roll centre what most people are concerned about is the height of the roll centre. If the roll centre is high it will reduce the amount of body roll that you get when on side slopes. This is a good thing because it keeps everything stable in the off camber stuff and is why a lot of people try to get their roll centre up high - to reduce body roll. The roll centre can be thought of as the point where the body is supported laterally (or sideways). So that if the body is supported laterally up high it wont have as much tendency to induce body roll than if it was to be supported down low. If a rig uses a panhard rod then the roll centre is the mid point of the panhard rod.

When you start to look at triangulated 4 links things start to get a bit more complex and you should be really talking about the roll axis as apposed to a single point. But in simple terms if only the upper links are triangulated then the roll centre is high (means less body roll) and if only the lowers are triangulated then you get a low roll centre (means more body roll). If both the uppers and lowers are triangulated then the height of the roll centre will still be high and the angle of the roll axis will be more horizontal. Now without going into it too much a horizontal roll axis produces little roll induced rear steer (which may or may not be usefull on a rock crawler). Also if you can get the roll axis to be sloping down a bit (going from the rear to the front) then it will behave better on the road (again this may not worry you on you trail rig)

Again this is hard to explain without going into things too deeply or writing 1000 words.

To further complicate things a high roll centre (or axis) isnt the be all and end all of rock crawler suspensions because what a high centre also does is if a wheel moves upwards (over a bump) then the body must move sidways as well (really should be drawing pictures here to help explain this). Now as you go faster for the wheel to move upwards quickly it must push the bodysidwards quickly as well - which is hard to do. What this means is that when you are throttling up a climb quickly (still talking rock racing speeds here ie say 40:1 and 4000rpm) when you hit a bump on one side your springs wont want to compress when you have a heigh roll centre because to compress a spring it must move the body sidways as well so you may as well think of it as having no springs at all and the rig will just bounce off the tyre.

Running a low roll centre will let a wheel compress much more easily without pushing the body sidways as much.

Lots of successful comp buggies run high roll centres and lots of then run low roll centres. One isnt definately better than the other.

So in summary:

If you want a high roll centre trianglate the uppers.

If you want a low roll centre triangulate the lowers.

If you want the rig to behave well on road at speed then you should look at triangulating both the uppers and lowers and try to get your roll axis sloping downwards a bit towards the front.

If you want to minimise roll induced rear steer then you should also do the double triangulated thing to get a flat roll axis (although having the axis a bit up hill or down hill wont matter just as long as its flattish).

If you want your suspension to work well on the heigher speed throttling climbs and soak up bumps then you should go for a low roll centre.

If you want your rig to work well on the slower crawling speeds and reduce body roll and remian stable in the off camber stuff then you should go for a high roll centre.

Finally the hieght of the roll centre or the angle of the roll axis wont really make a huge difference to the capability of a rig - we are only talking degrees here. Lots of very good comp buggies run every variation of roll centre and axis.

I was going to do a bit on the IC and anti squat as well but that just took me an hour and it probably didnt come out very well anyway. So I will do it later of nobody else does or I dont agree with them.

Sam

PS this is all just my opinion and is stuff that I have worked out myself kicking around here and real world observations. I have never read a text book on this stuff so I could be way off the target but I dont think so.
 

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I designed the shit outta mine. Ran numbers, 3D cad data, blah blah blah. Then I shit canned all that and put shit where it actually fits, and looks right. Guys that know whats going on probably cringe about that:D The things is: I can run all the calcs, but it comes down to me not knowing what a 5% increse in AS will do to my rig. I don't know anyone with my exact rig, either. So pretty much I have mine together, and I am gonna run it, fawk around with changing it one variable at a time, so I can get some data on what does what.
 

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anyone with pics of their links that they can post of here?
 

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How about some info on front link suspensions?

When designing the front should you make all your anti squat and roll axis measurements based on the same point (COG), obviously the distance would be shorter to the COG from the front than the rear (in a jeep or truck type anyways). Does that matter? Do you just make the links accompany this shorter distance or do you make the links the same length as the rear links? Should the front have similar anti dive/ dive or more/less than the rear? Should the roll axis be equal to, greater than or less than the rear? Any other info on a front link susp that would compliment the rear would be great.:idea:
 
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