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Old 07-23-2008, 02:29 PM   #1 (permalink)
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Suspension geometry for GETIN IT!

I’ve been chatting with several people in the industry about a build I’m about to begin. Having very little experience in Desert Racing and higher speed offroad, I’ve been talking to people about their theories in suspension design for GETIN IT. Here’s the rundown of what Jess and I have been shootin back and fourth……

Quote:
Originally Posted by Bent Fabrications
I'm about to start a pretty cool build and I'm trying to do some planning. Things are going to get tight in the suspension department quick and I'm trying to debate whether to do a 4 link front or 3 link.

I've noticed most everything your building lately is a 3 link front and rear... I know that properly set up a 3 link is supposed to "equally load" the tires. Do you really think it's a better choice... or is it more a matter of available space? Really, with the pulley set up on the LS1 and having a pass drop front I think the 3 link would be the easiest fit.

I'm interested to know a few of your thoughts if you had the room to do either.

Some of the specs of the buggy are: 609 pass drop front and centered 9" rear. Mega9 in the rear with a low pinion Nascar third in the front. I'm shooting for 6.5" up in the front and 7.5" up in the rear. 14" Racerunner coilover with res and 2" Air bumps in the front, 16" Racerunner emulsion coilovers set up as coil carriers, 2 tube bypasses, 4" Air bumps, and currie sway bar in the rear, TurnKey 390hp all aluminum LS2, NV4500 ( i know.. don't give me no shit, it's the customers choice not mine), 3 speed Stak "mini case" (the first one sold), 40" Nito mud graplers on 20x10 Spiderlocks and I'm making it street legal, and installing A/C.... yes I said A/C on a buggy

The chassis is going to be simular to our Cliffhanger but extended out to 110" WB (20" at the belly at ride) I'm adding in a little extra Cargo space inside... along with a books worth of cool extra features...

I will be doing a buildup thread, Chassis starts next week. Anyway, I'd appreciate some thoughts on the front suspension. The ability to be stable at high speeds is a must (60+mph) I'm doing a 4 link rear with a pretty low roll center to help soak up bumps at speed... just really not sure which way to go with the front.

-Tim
Quote:
Originally Posted by mudtruck44
Wow, sounds like a big build. I had to go 3-link on my buggy. There was no room front or rear. I don't think you will notice a huge performance difference in the front with 3 vs 4 link. I kinda think that a 4-link rearis better than a 3 link rear though. The high roll center and a track bar can cause the suspension to lock up when the weight is transfered to the front and the rig is off camber. It sucks bad when that happens. Anyway, I think the 3-link will work just as well in front. I don't understand your comment about the low roll center helping high speed handling. That really shouldn't make a difference.
Quote:
Originally Posted by Bent Fabrications
About the roll center being high or low in suspension design...

At risk of typing a book, here's a quick take on my experience and understanding of designing 4link setups....PLEASE CORRECT ME IF YOU THINK I'M OFF.

When I design a system and notice that the roll center is high in the software, I've also noticed the suspension seems to "swing" more when it cycles. Meaning, the body shifts more side to side as the suspension travels, or the axles seems to move to one side or the other as it compresses or droops. Meaning, as the axle hits a bump or travels up or down, the body of the rig must move to the side slightly at the same time. Some people think this adds stability in slow speed situations like crawling and side hilling....however, I would think this would be less desirable in a rig being built for higher speeds. I don't want the body getting upset by the side to side shifting that occurs as the suspension is cycling through whoops and ruts. Does that make sense? Typical high roll center setups are 4 links with straighter lower links and triangulated uppers coming together on the axle end.

A great compromise to lower the affects of rear steer and "axle swing" (for lack of the correct term?) is to double triangulate the uppers and lowers. If you run numbers on the same setup above but pulling the lowers closer together on the chassis end, the roll center will come down.

If you build a system with straight uppers and triangulated lowers coming together at the chassis side, you can achieve a roll center barely above the axle center line. This type suspension moves the body very little during it's range of travel... meaning very little "resistance" to the suspension travel induced by the body. Does that make sense? I would think this would be the best choice for a faster buggy?

The concept I'm talking about is kind of hard to explain. and it doesn't apply at all in a three link setup as the "swing" of the axle I'm referring too is completely controlled by the location and length of the pan hard bar mounts and the roll center is always the height of the pan hard (if it's level at ride height).

I'm sure there is some term for what I'm talking about, but the observations of the amount of "swing" an axle has in higher or lower roll centers in different suspensions is definitely noticeable, and I think there is a place for each...I think, Faster speeds= less resistance to suspension movement desired=lower roll center desired vs. Slower speeds=a higher roll center(with more body resistance)=more stability.

Does this sound right? I like to say I understand more than the average guy, but a lot of theory's come from observing what works and trying to understand why it does. So many competitors are going to a three link front. I know I can get very comparable numbers with the 3Link as the 4 link (and have more space available in the chassis)... And I also understand the formula to create equal loading on the front tires, just wandering if it really is a better setup for the front or not. I've never had the opportunity to run both setups on the same chassis to compare theory to real world feedback... but I know your shit works great. There are very few builders willing to talk about this stuff…
I was just wandering if there is something everybody else knows (that I don't) that's making so many people go with a 3 link on all these new buggies?

I haven't locked in which way I'm going to go yet (in the front), but need to decide before I start building... I agree that a 4 link in the rear is the better option (space providing).

I can't wait to get on this build... It's going to be badass! Not really a comp buggy, but a recreational buggy designed to haul ass.

-Tim
Quote:
Originally Posted by mudtruck44
I understand what you're saying, but I don't think its as much of an issue as you think. If we're talking about the rear axle articulating 10-15 degrees going through whoops at 60 I don't think its moving side to side much, and I don't think it would resist travel.

If we were talking about rock racing through boulders I would have to agree with you. It would be better to keep the roll center a little lower to keep it from swinging off the side when it’s flexing out. I consider a high roll center like 34", a low roll center would be 18". I think somewhere in between would be a decent place to shoot for with what you're talking about.
Quote:
Originally Posted by Bent Fabrications
Kinda blury but this is what things look like on paper. A three link would have very similar numbers. I'm more cautious with this buggy than those in the past because of the speeds he's requesting. I think it looks good, based off the performance of previous buggies built on this platform. The rear end will have 71%AS at full bump 82% static and 106% at full droop. The front has a slight amount of recession as it travels up with a static AS of 63%. We are only working with the stock steering angles of the 60 outers but it is possible to move the lowers closer together in the front if necessary for link clearance. Hope it works good. I'll have very limited testing with this rig before it gets shipped to Mexico to the owner....

Quote:
Originally Posted by mudtruck44
I think it looks pretty good except one thing. I think the anti-squat is a little high for high speed rough stuff. If you're on it hard going over chatter bumps the rear end is going to get stiff with that much AS. I've asked a few desert racing guys about this too. They say they run almost no AS on trophy trucks, and other solid rear axle race trucks. Just something to think about.
Quote:
Originally Posted by Bent Fabrications
This program translates "no lift transfered through the links during acceleration" as 100% AS... with weight transfer, 80ish% should squat a little on acceleration. At one inch from full droop, it would be at 100% AS making the chassis neutral? or barely trying to lift (to help get unstuck if high centered)... That's good info about the desert trucks. Living in the East, I don't get to see many desert trucks fist hand. My buggy is set up at 106% in the rear for East coast wheeling... I generally think around 60% is a good number for the high traction out West... but high speed is a little different. Do you think I should bring it on down to around 60% or less?

-Tim
Quote:
Originally Posted by mudtruck44
Honestly I think you should post the question in the Desert section here. I've been thinking about posting the same question in concern to setting up the rear of my Willys for KOH. I've talked to a few people about it, but I'd like to see what other would say.
So here we are, I’m bringing the discussion to the board. The questions are:

1. What are the opinions of 3 link vs. 4 link front suspensions? If you had the room to do either which would you choose and why.
2. When talking about GETIN IT in the rough stuff at speed, what are good suspension numbers to work with?

Opinions and ideas of how well what I’ve laid out will work are welcome…Buggy’s that can HAUL ASS being a hot topic lately, I’m interested in the theory’s of what people think work well GETIN IT when it comes to suspension design.

-Tim
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Old 07-24-2008, 09:12 AM   #2 (permalink)
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subscribed. linking my cruiser to go beat the shizzle out of it. F dodge 60 w/ 14 inch remote SAW's and jounce shocks. prolly going to 3 link w/ a long panhard due to packaging issues, and how low i want to keep the rig.
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Old 07-24-2008, 09:56 AM   #3 (permalink)
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Don't have much time, but have been through this recently..

3 link or 4 link? Don't care.. I can make both act close enough to the same way. Given no drag link or space constraints I pick 4 link unless there's some reason I want panhard rod jacking.

Now..
100% anti-squat is NOT neutral in the calculator, however, it depends on how you define neutral. It is not my definition of neutral. You said 100% AS means "no lift transferred through the links during acceleration". This isn't correct. The idea is that at 100% there is a lot of lift from the links and that lift is exactly equal to the amount of transferred load that would otherwise compress your suspension/springs. Now the chassis doesn't net lift, but due to physics it should squat, so the amount it doesn't squat that it should is the "lift" generated by the links. So at 100% AS all load tranfer during acceleration is handled by suspension links and not seen through the springs. To me, that is far from neutral. Neutral is 0%. That's when the load transfer goes through that which is designed to carry it without secondary forces (like links) restricting the natural movement. I can tell you at speed you're better off sending loads and movements through the things you can tune (shocks/springs) and not things you can't tune (links). Unless you have a specific need for generating force via an anti- like the front of Nextel Cup cars where rules limit what they can achieve through better means it is best to avoid them.

AS is also directly related to the path the axle contact patch follows during compression and droop. 0% AS equals a contact patch that moves perfectly vertical with relation to the chassis centerline. If it moves rearward under bump and forward under droop you'll have some AS and the more severe it deviates from vertical movement the higher the AS number becomes. Now think about how you want your contact patch to travel.
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Old 07-24-2008, 10:45 AM   #4 (permalink)
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Bigger Valves,

You do a much better job of typing out AS than me... the way you described it, is what's in my head (100% is the balance of forces generated by the links vs those created through weight transfer)

However, the rest of what your saying is EXACTLY the info I'd like to discuss. From what I understand you to be saying... is that for the higher speed stuff, you would rather completely control the suspension with the shocks (which are tunable) than the links having some input (more than 0% AS) I understand this, and it makes perfect sense, in theory.

With this in mind, how much AS would be acceptable, and has proven to work well in the real world, not just theory. I can easily adjust down to ~62% just by using the top hole in the bracket for the uppers on the chassis. To get less than that will require some changes to the design. (this is not built yet, so making changes requires nothing more than an eraser at this point)


Also, while I have your attention, did you have any theories on low roll centers vs. higher roll centers for a suspension designed for speeds?

I feel like I'm treading into territory that is info people just don't share and understand that bigger teams are not going to give out their "secrets" of going fast. But some general discussions of why people built their setup the way they did, what they were trying to achieve (in theory) and how well it worked out is good info.

-Tim
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Old 07-24-2008, 12:25 PM   #5 (permalink)
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Subscribing. Good stuff.
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for AZ crawling and trail runs
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Old 07-24-2008, 10:18 PM   #6 (permalink)
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definately subscribing to this... good stuff.
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Old 07-24-2008, 11:35 PM   #7 (permalink)
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Seems like a good topic, but how about some more tech info?
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Old 07-25-2008, 05:38 AM   #8 (permalink)
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bent fab.- my first suspension looked like the last one you posted, I dont think it handled very well at speed or in the woops, it would always be very rigid when hitting the face of the next whoop, much like Bigger Valves described where the forces of traction are being transfered through the links rather than the springs and shocks. that was with a 98" WB so that might have had a little something to do with it but with some slight changes and 4 more inches of WB it absorbs the whoops much better....

take it for what it's worth.
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Old 07-25-2008, 06:04 AM   #9 (permalink)
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Slight changes as in what? Changes in geometry to make more wheel recession from static ride height through bump travel... lowering the AS from what it was to let the shocks work more... just the change in WB... The longer links used to get more WB... What did you do that you think made the truck work better now than before? I would think just the longer WB alone would help you out. Along with getting some more weight on the rear end. I think most of our rock buggies are so light in the rear that the rear suspension struggles to perform good at speed anyway. Just the weight of hanging a 40" spare tire back there seems to smooth things out a bit...

Others out there? Like Jess said.. bring on the tech!

-Tim
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Old 07-25-2008, 06:11 AM   #10 (permalink)
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Quote:
Originally Posted by Bent Fabrications View Post
Slight changes as in what? Changes in geometry to make more wheel recession from static ride height through bump travel... lowering the AS from what it was to let the shocks work more... just the change in WB... The longer links used to get more WB... What did you do that you think made the truck work better now than before? I would think just the longer WB alone would help you out. Along with getting some more weight on the rear end. I think most of our rock buggies are so light in the rear that the rear suspension struggles to perform good at speed anyway. Just the weight of hanging a 40" spare tire back there seems to smooth things out a bit...

Others out there? Like Jess said.. bring on the tech!

-Tim
less anti squat ~60%
more frame seperation~5"
a little more axle seperation~8.5"
longer links ~42" lowers
longer wheelbase-102.5"

my only "at speed" stuff has been the silver lake sand dunes and at the badlands... I've never spent hours in the desert.....
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Old 07-25-2008, 12:32 PM   #11 (permalink)
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We built a TJ at the Badlands that was set-up for "go fast". It had close to 0% AS, resevoir coilovers and air bumps. It was killer in the whoops. It looked like a trophy truck blasting through the rough stuff.
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Old 07-25-2008, 03:46 PM   #12 (permalink)
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Jess,

I know your current buggy has close to 0% AS too. If you set it up a little higher, do you think it would do good haulin ass? Or, do you think other factors that make it do good crawling would have to be changed to make it handle well getin it....

I guess I'm saying, are the theory's used to setup for crawling the same as the theory's used for haulin?

As I said earlier in the thread, I think there is a difference between what works here in the East on our clay, mud, and loose rock... and what works well in the higher traction of the West. It sounds like a setup that would work great here with a higher roll center and higher AS numbers would not be a good choice in the West in either situation of Crawlin or Haulin... But it does sound like some of the same design concepts for what works in the boulders and open desert are similar??

So... is their perhaps an Ultimate setup that will both Crawl and Haul?

We're just talking theory... I know others have thoughts on this. Speak up, If you have something that works well, do a quick study of it and post why you think it does... and what you might change that you think would make it better.

-Tim
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Old 07-25-2008, 08:57 PM   #13 (permalink)
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Is this rig to be intended mostly for 'haulin and not very much rocks? I'll assume no because of the 3 speed case. I don't want to be a naysayer and I'm sure you know that by setting the suspension up with 0% anti-squat, it's probably going to suck for steep climbs. Might be ok if you winch down both axles to the bumps though and hang on.....
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Old 07-25-2008, 09:45 PM   #14 (permalink)
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No... the rig I'm about to start is going to be pretty universal. But, thinking about the terrain it is intended for raised some questions about how to design the suspension. I'm going to give it a range of adjustability that should cover about anything the owner wants to use the vehicle for. But the terrain is very simular to what would be expected from a rock racer or rig built for KOH. I feel it's a hot topic right now that's on many builders and teams minds. What do you put into the design?... what compromises do you settle for?

But each builder has different theory's about how things should be designed/built. I like to hear them... I started putting together ideas and theory's about suspension design by watching rigs that I thought worked good, and trying to determine why it works good (or doesn't). We've built some that didn't work well at all (though on paper it looked great) and some that we threw together "eyeballing it" and it performed excellent. What I'm getting at is sometimes ideas of what work good on paper don't work well in the real world of offroading because of the infinite number of variables. The ground moves beneath us...

Your saying a vehicle with close to 0%AS wouldn't climb very well. We all watched Jess's buggy (with close to 0%AS) climb seemingly impossible lines nobody else could run all season. In theory the suspension would squat something terrible... maybe even to the point of wanting to pack the front wheels end over end? But that is clearly not the case in reality, his buggy climbs great. Is this because when the rig is at a 50degree angle the weight carried in the links completely changes the dynamics of the suspension?

Just food for thought.
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Old 07-25-2008, 10:02 PM   #15 (permalink)
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Originally Posted by Bent Fabrications View Post
Jess,

I know your current buggy has close to 0% AS too. If you set it up a little higher, do you think it would do good haulin ass? Or, do you think other factors that make it do good crawling would have to be changed to make it handle well getin it....

I guess I'm saying, are the theory's used to setup for crawling the same as the theory's used for haulin?

As I said earlier in the thread, I think there is a difference between what works here in the East on our clay, mud, and loose rock... and what works well in the higher traction of the West. It sounds like a setup that would work great here with a higher roll center and higher AS numbers would not be a good choice in the West in either situation of Crawlin or Haulin... But it does sound like some of the same design concepts for what works in the boulders and open desert are similar??

So... is their perhaps an Ultimate setup that will both Crawl and Haul?

We're just talking theory... I know others have thoughts on this. Speak up, If you have something that works well, do a quick study of it and post why you think it does... and what you might change that you think would make it better.

-Tim
My buggy is not really a typical buggy. The rear sprung weight is like 300lbs. It will work ok for getting it if you stay hard in the throttle. If you coast over anything rough the suspension doesn't move.

Personally I think you can run higher AS #'s on the west coast. With the large smooth rocks out here the tirse can stay planted under throttle. On the east coast the loose rocks and ledges will make the rear end bounce with too much AS. I had two east Pro-Mod guys call me after the second event because they were having trouble making some of the climbs. I asked them what kind of climbs and about thier rear suspensions. Both of the had higher AS and weren't making the climbs with rough series of ledges.



This is one of the climb the higher AS rigs were really struggling with. In the past 3 event there I watched a lot of buggies attempt it, and the rigs with close to 0% were making it look easy.

Quote:
Originally Posted by desertCJ View Post
Is this rig to be intended mostly for 'haulin and not very much rocks? I'll assume no because of the 3 speed case. I don't want to be a naysayer and I'm sure you know that by setting the suspension up with 0% anti-squat, it's probably going to suck for steep climbs. Might be ok if you winch down both axles to the bumps though and hang on.....
Actually a lot of buggies are running AS close to 0%, mine included. I rarely touch my winch unless I'm crawling an incline probably 60* or steeper. There's a big difference between running 0 AS on a 3000lbs buggy with a 19" belly, and 0 AS on a 4200lbs trail rig with a 25" belly.
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Old 07-25-2008, 10:33 PM   #16 (permalink)
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Yes there is a big difference between a moon buggy and a linked trail rig. I can only speak from my experience and we all know that there are usually a lot of variables in 'wheelin. My buggy with a little over 100% AS seemed to climb better then when I had around 80% AS. Of course the 100% rig had about 10" of more wheelbase. I've never had the shocks to be able to REALLY go fast(Air shocks that weren't really setup for it). I don't have enough knowledge there to have any usefull input...

I'd love to read more about this topic, of course nothing works best for everything and if it did....we could all build suspensions with 0% AS and kick ass everywhere we went
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Old 07-25-2008, 10:36 PM   #17 (permalink)
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Agreed that too much AS will cause wheel hop when traction is touch and go. But can be good when traction is consistently available or consistently not. I ride on way more dirt than rocks and like to see close to 80% AS or higher. For consistent high traction (what I call West coast) I'm more comfortable erring on the side of less AS for predictability and build in some adjustment to gradually step up to works best for that rig.

Jess, you say if you let out of the throttle the suspension doesn't move? I understand that your goal in the buggy was not to haul ass, but according to the theory's above The lower AS should make the shock be the determining factor of how well the tire follows the ground? or do you think something else about the design would cause this? EDIT: not under power AS should have nothing to do with this.

You also mention how light the rear of the buggy is... this would have a huge affect on amount of weight transfer. Hence your statement of "There's a big difference between running 0 AS on a 3000lbs buggy with a 19" belly, and 0 AS on a 4200lbs trail rig with a 25" belly." Is that because you feel the additional weight needs the additional AS to help resist the weight transfer?

What if I had a 3000lb buggy and decided to hang a 40" spare tire on the back? would it need more AS to help counter the weight?

I don't feel there are right or wrong answers, but it's interesting to think about it...

-Tim
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Old 07-26-2008, 01:21 AM   #18 (permalink)
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100% anti-squat is NOT neutral in the calculator, however, it depends on how you define neutral. It is not my definition of neutral.
I don't think 0% is neutral either, I'm not even sure neutral can be used to describe antisquat. Neutral is typical used if the input to the system is the same as the output.

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So at 100% AS all load tranfer during acceleration is handled by suspension links and not seen through the springs. To me, that is far from neutral. Neutral is 0%. That's when the load transfer goes through that which is designed to carry it without secondary forces (like links) restricting the natural movement. I can tell you at speed you're better off sending loads and movements through the things you can tune (shocks/springs) and not things you can't tune (links).
I would agree to a point. I think it depends more on the spring rates you are using, if they are fairly stiff they will prevent squat and you can run low AS numbers. If your running fairly soft spring spring rate you can run more AS. With desert racing traction is typically low help keep the squat down as well.

However it seems like when encountering a bump the traction would increase and could cause the suspension to lock with high AS. I don't think this is due to the AS but the wheel trying to follow the arc of the wheel travel as the bump is trying to push the wheel in the horizontal direction.

It seems that AS is being given too much credit for what is going on with these systems. AS determines how much of the acceleration load is directed through the links or the suspension, but it would seem the end resultant force is the same.

I would think if there is enough traction to actually cause squat in the shocks you would want to run some AS to save the shock travel to control the ride. Which maybe why West Coast trucks can run higher AS compared to East coast.


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I guess I'm saying, are the theory's used to setup for crawling the same as the theory's used for haulin?

But it does sound like some of the same design concepts for what works in the boulders and open desert are similar??
It should be. Vehicle dynamics is pretty universal and what applies to road racing applies to off-road racing it just that the setups will be different. It's understanding the system as a whole and being able to apply it to different situations. Not sure if that is very clear but the same vehicle dynamics calculations that out Formula team uses we use on our Baja car. We run ~63$ AS on the rear of our cars and it works great, IRS, soft spring rate and low unsprung weight though.

High roll centers seem to be working well in the West too. It gives less body roll there by leading to a more stable feeling rig.

Seems race cars can run roll centers at ground or below ground which means less unsprung weight as everything above the RC would be controlled by the springs or considered sprung weight; but it also leads higher spring rates (also help control the bodyroll), much higher then I would think would work well for Crawling and desert racing. Low RC also would use wheel travel in roll leaving less travel for ride. It's been mentioned that with high roll centers the load is transferred by the links and a Low RC is through the springs. I prefer to keep the suspension to deal with ride and allow the links to deal with the rest.

I'm not a expert on any of this though and always am trying to learn and understand more.
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Old 07-26-2008, 06:50 AM   #19 (permalink)
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I'm not a expert on any of this though and always am trying to learn and understand more.
I'd never say I was an expert either... please don't take anything I say as LAW. I'm just trying to get some people to talk about suspension.

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High roll centers seem to be working well in the West too. It gives less body roll there by leading to a more stable feeling rig.

Seems race cars can run roll centers at ground or below ground which means less unsprung weight as everything above the RC would be controlled by the springs or considered sprung weight; but it also leads higher spring rates (also help control the bodyroll), much higher then I would think would work well for Crawling and desert racing. Low RC also would use wheel travel in roll leaving less travel for ride. It's been mentioned that with high roll centers the load is transferred by the links and a Low RC is through the springs. I prefer to keep the suspension to deal with ride and allow the links to deal with the rest.
I've seen very successful rigs that use high roll centers and also very successful rigs designed with lower roll centers in crawling... But I've always thought that a higher RC created resistance to suspension movement, giving the rig a more stable feel by carrying some of the load (and being able to run softer springs as a side advantage as you mentioned). The resistance coming from a number of things that are happening during the range of travel, including side to side movement of the body as the suspension articulates. So in theory, I would think for Getin IT... a lower RC would be a looser suspension able to move more freely across the terrain at speed?? Now when I say low RC, I'm not talking about ground level as in the road racers... I'm refering to levels close to the height of the axle and or skid plate of the rig. Anybody else have thoughts on this?

-Tim
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Old 07-26-2008, 11:15 AM   #20 (permalink)
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Agreed that too much AS will cause wheel hop when traction is touch and go. But can be good when traction is consistently available or consistently not. I ride on way more dirt than rocks and like to see close to 80% AS or higher. For consistent high traction (what I call West coast) I'm more comfortable erring on the side of less AS for predictability and build in some adjustment to gradually step up to works best for that rig.

Jess, you say if you let out of the throttle the suspension doesn't move? I understand that your goal in the buggy was not to haul ass, but according to the theory's above The lower AS should make the shock be the determining factor of how well the tire follows the ground? or do you think something else about the design would cause this? EDIT: not under power AS should have nothing to do with this.

You also mention how light the rear of the buggy is... this would have a huge affect on amount of weight transfer. Hence your statement of "There's a big difference between running 0 AS on a 3000lbs buggy with a 19" belly, and 0 AS on a 4200lbs trail rig with a 25" belly." Is that because you feel the additional weight needs the additional AS to help resist the weight transfer?

What if I had a 3000lb buggy and decided to hang a 40" spare tire on the back? would it need more AS to help counter the weight?

I don't feel there are right or wrong answers, but it's interesting to think about it...

-Tim
My buggy is not "neutral". It transfers a decent amount of weight to the rear when you're on it hard. Because of that the shocks have to be stiff enough to handle the weight transfer. When there is no weight transfer the shocks are way too stiff. Its kind of a pain in the ass, but the only place it sucks for rockcrawling is it unloading worse than normal on down hills.

The ? about the 40" spare, are we talking about crawling or go fast? Crawling I would think you might want more AS. In general we're using AS in rockcrawling to compensate for weight transfer when were climbing hills. For going fast the cars are staying on flat ground most of the time so they don't have to set up a suspension to work at a 60 degree angle. Lets stick to talking about high speed stuff.
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Old 07-26-2008, 11:37 AM   #21 (permalink)
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so in the most basic language you could tell me, what should my links look like? when i start reading a ton of link discussion, my mind always goes and i get


my setup is low, i dont like high rigs.
my lower links should be as flat as possible, but having to angle them for clearance is the give and take

my upper should mirror the bottoms, but should have some triangulation to the bottom links that intersects somewhere over the rear axle maybe a little past it, right?

my panhard should be as long as possible, and mirror the drag link.

i want to beat my cruiser. im tying in the front suspension and hoops to the main cage to help with loads applied to the frame. hopefully ill be able to tell someone in this thread to bring your own neck donut, and adjust the passenger ohshit handle accordingly

thanks guys for the info, i hate it when threads like this go off track and turn into a shit storm, its hard to find meat and potatoe threads
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Old 07-26-2008, 11:46 AM   #22 (permalink)
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Continuing off of what Jess is asking about the spare... most of the rigs we build here in the shop end up with very close to 55/45 front to rear weight bias.. From what I understand, many of the desert rigs run more weight bias in the rear to "help the suspension work" and to help carry the front floating through the whoops. I think the additional weight of a spare on the light rear end of our buggies could help make the suspension work better??? It is maybe a bonus side affect of something needed in the desert anyway... But along this line of thinking, what kind of weight bias would look good for a rig designed to Get It...and handle trails like the Hammers?
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Old 07-27-2008, 08:57 AM   #23 (permalink)
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Great thread so far...just some quick thoughts. I'd try for some 3 tube bypasses over the 2 tube as it gives far more adjustability in the compression stroke. What kind of spring rates you choose will effect to a large effect how well your suspension may or may not perform in the whoops. I understand that your spring rates will be quite soft but so are many desert and to a certain extent many closed coarse off road race cars. Preload on the springs is very very important part of set up on our CORR Pro 2 truck and I'd guess it would be important on a crawler/hauler so pay attention there. Also why choose emulsions over resevoirs for a go fast rig? I'm not sure why but on street driven "canyon" cars and road racers (and even in lower speed auto-x). I've never been happy with traction (really sudden break away) characteristics with adding a panhard bar to any suspension that did not need one anyway ie leaf spring cars etc. Not sure how this would relate to comparing a 3 link or a 4 link but in the rear cornering or even possibly side hilling at the limits of available traction I think the very solid panhard bar might cause the sudden breakaway effect that I hate.
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Old 07-27-2008, 10:00 AM   #24 (permalink)
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Preload on the springs is very very important part of set up on our CORR Pro 2 truck and I'd guess it would be important on a crawler/hauler so pay attention there.
Now this is where some good tech could be added, anyone care to elaborate more on how the preload is setup on the trucks?? Considering so many of the coilovers we see running around have springs "hanging loose" at full droop, I think this is a greatly overlooked part of setting up the suspension with many rigs out there..


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Also why choose emulsions over reservoirs for a go fast rig?
I'm setting the rear coilovers up to mainly be coil carriers and plan on letting the Bypasses do most of the work. Keep in mind I'm building sort of an all round rig. (And this thread isn't neccessarily about the specific rig that I'm building, but where we are as a sport) Just the fact that we are using a setup with bypasses is a MAJOR step up from what most of the rigs that serve time in the rocks have. Considering many of the rigs in KOH are running nothing more than 2.0 Air shocks and debating amongst themselves if simply stepping up to a 2.5" body is going to be sufficient... Are bypasses overkill in the rocks? I think so. Do they hinder or hurt performance in the rocks? I don't see how they could... but I can definitely see how they could help the rig HAUL A$$ in between.

I feel like The sport is definitely progressing to the point that people have to start thinking about tuning there suspension... EVERYTHING about the suspension. From geometry of the links and the affects they have on the chassis, to what type of dampening control to use (Air shocks vs. coilovers and possible additions like Air bumps, Bypass shocks, etc.), down to valving and spring rates. I think other forms of offroading are still leaps and bounds ahead of "Crawlers that are trying to go fast"

I'm more than interested in listening to what the guys haulin across the desert successfully have to say. In my opinion, as our sport is continuing to push in a new direction, this should be the hottest topic in our sport right now for anybody that plans to keep up.

-Tim
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Old 07-27-2008, 03:27 PM   #25 (permalink)
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However, the rest of what your saying is EXACTLY the info I'd like to discuss....

With this in mind, how much AS would be acceptable, and has proven to work well in the real world, not just theory. I can easily adjust down to ~62% just by using the top hole in the bracket for the uppers on the chassis. To get less than that will require some changes to the design. (this is not built yet, so making changes requires nothing more than an eraser at this point)
I'm going to go through the thread here and pick out some stuff and hopefully clarify and generate some more discussion/understanding. I can't tell you a number that is acceptable. I do think this crowd, especially PBB, talks and worries about the variable anti-squat way way too much. It's one parameter, sure, but there a basic vehicle specs that relate to vehicle dynamics that mean much more and also dictate how much anti-squat may or may not be acceptable. 62% for a go fast truck in my opinion is too much. People have used that much and more and been successful, but I think if you talk to someone who really understands vehicle dynamics they would not choose to build it this way. Listen to what Jesse is saying. I've seen him now mention great performing trucks both rockcrawling, climbing, and go-fast with 0%ish anti-squat numbers. I think low is better for EVERYTHING from crawling to go-fast. I know higher works, but I think that stems from guys building setups on crawlers the traditional way (which just simply lends itself to some highish amount of AS) and then finding it works well or better than something else, but it's not correct thinking to then assume it's that AS number that makes the truck overall perform well. That's the problem.

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Also, while I have your attention, did you have any theories on low roll centers vs. higher roll centers for a suspension designed for speeds?
Lowish roll centers for me. High roll centers create an anti- under lateral forces, just like anti-squat creates an anti- under longitudinal forces.

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I feel like I'm treading into territory that is info people just don't share and understand that bigger teams are not going to give out their "secrets" of going fast. But some general discussions of why people built their setup the way they did, what they were trying to achieve (in theory) and how well it worked out is good info.
You are correct here. I will help lead you in a direction, but I will not tell you what to do because that would be foolish. I believe the most important thing I can do is help people understand the proper physics at hand to then have a better understanding of what's happening with suspensions and the parts so you can reason the decisions yourself. If YOU don't believe in what you're doing it'll never work.
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