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Suspension guide


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To find target caster, follow the formula below:

WB = wheelbase in inches
R = rake in degrees
C = caster in degrees
RH = ride height in inches
MC = minimum clearance
E = error factor in degrees

MC should be +1” for TT and FT, 2” for desert, and 1.75” for all others.

E is an error factor for unforeseen circumstances. Rough terrain, do nothing. Smooth terrain, remove 1-2 degrees. Average terrain, remove 1 degree. New and expert riders (be honest with yourself) do nothing. Everyone else, remove a degree.

SinC = (RH-MC)/(WB-sinR(RH-MC))

C+E = target

I never really remember any formula I write and have to derive them in my head every time. I made a mistake with post formula error correction above and can’t edit the comment.

I quoted the original comment and fixed it in the quoted section.

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  • 1 year later...

I haven’t been very active online for quite a while since changing around almost everything in my life. I keep getting people asking the same questions and I’ve changed my views on a few things over time. I’ll add more here and there but it’ll be short and sweet for now.

Long travel is not needed for a banshee rear. It isn’t needed for most quads.

Long travel isn’t necessary but if you’re buying shocks and arms anyway, it’s a no brainer.

99% of all people who tell you what suspension or chassis setup is good just legitimately don’t have a clue. This goes all the way up to most builders who actually build arms. I also spoke with a pro rider the other day that asked if a vented hood was going to give him better lap times, so yes, your heroes are full-on space cadets as well. A few know things, but not many these days.

“5 years no issues” means almost nothing to fabricated parts. It may have sat for all of it and your “huge air” is probably a 36” tabletop. You may have gotten a set that is only being held together by luck and not know it because you just can’t ride.

There are 2 companies in the US who currently manufacture arms with any sense of modern engineering in mind: Lonestar and LS4. Lonestar has the budget. LS4 is where I used to work. The rest use the ideas from past generations of builders or hear say. All competition arms are made from 0.083” -0.120” wall chromoly or DOM for the lowers, 0.065-0.120 wall chromoly or DOM for the uppers. I know because I’ve repaired all of them. There is almost always no testing beyond the first model that a product is made for, with the rest just changing to fit and using the previously proven principles.

“I got shocks setup for my weight and riding style” is the equivalent of saying, “I got shoes for my feet and walking style.” It’s a given. Stop saying it.

Alba is still Chinese garbage with dogshit welds. When they admit it, I’ll get off their case. They’re the beats by Dre of 4 wheelers.

My current stance on the best arms available are Lonestar DC-Pro. I won’t air anyone out because some of them are my friends, but I’ve repaired shit that I shouldn’t have to repair. “Stackin dimes” isn’t going to make it an x-ray grade weld. If I had a dollar for every pretty weld I’ve had to cut out and repair… Anyway, the answer is Lonestar DC-Pro. If you ask, “but what about _____” then my answer is still the same. Save for some off the wall shop that’s making one or two arms here and there, I’ve been in all of them and I’ve already considered the question. If I/we release a set of banshee arms, I’ll come here to let you guys know.

Lightweight stuff and hillshooter builds are not my area. I won’t speak on anything that isn’t MX/XC/Desert oriented until I’ve gotten more into it.

-DDQ 4 Prez

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Update 2 since my last post from 30 seconds ago apparently didn’t upload and was saved as a draft.

Just a few thoughts and whatnot.

From above, Roll Design also make stellar components. Don’t know why I didn’t mention them.

An a-arm is just a piece of hardware. Nothing special. Choose the arm based on who has the best shock program (Roll Design by miles).

Another thing to note with putting a setup in the quad is that with more toe comes a solid change in ackerman. With racing vehicles, anti-ackerman is almost universally desirable simply because of tire slip angles. Therefore, more toe can mean significantly faster lap times. If you don’t care to corner, just keep the tires perfectly straight or VERY slightly toed in.

To get an idea why, look at lateral and vertical load forces for tires, tire slip angle, and don’t look at tires in terms of what some call “the bicycle tire model” where tires are a rigid entity that don’t flex and warp and deflect constantly. Tires move around A LOT.

More pressure keeps steering somewhat predictable but sacrifices tire compliance. Less pressure does the opposite. My approach has always been to run the pressure high and then gradually lower it until the tires start to fold under the rims. At that point, add another half pound and call it good. As you get faster and get the suspension and steering dialed in, you may need a little more air pressure since you’ll be loading the tires a more.

My views these days is that chassis geometry is most responsible for vehicle dynamics whereas the shocks are most responsible for the contact patch. Expecting shocks to do the job of the chassis is like dumping nitrous to fix a rich tune; you CAN but really shouldn’t expect it to go well.

You need enough ride height to keep to be able to take impacts without the compression being too high and to keep front body roll down. Seems counterintuitive but roll center becomes a factor.

If you do look into roll center, don’t forget to factor in that the force isn’t technically correct when viewing it as straight on and as simplistic as diagrams will illustrate. Tire jacking on the inside, tire compression from loading, the lateral force of the tire and contact patch mean center migration, and that the force is rotating the vehicle around the vertical axis (yaw) all matter to having a comprehensive view of what is actually happening.

Also don’t forget that with a solid rear axle, you don’t have a roll axis (roll center diagram from front and rear with a line drawn through them), but rather a roll triangle. This is basically the center of the contact of the rear outside tire drawn through the front roll center where the corners migrate several inches. Seeing it from above is pretty simple but there is a definite 3D aspect that has to be considered since the rear contact patch is at ground level whereas the front roll center is several inches (or a foot) above the ground. For this reason, I’ve changed my views on the rear being slightly wider than the front to where I believe the opposite is true. This narrows the width of the rear of the triangle and can keep the front suspension slightly more flat in the front while canceling out any diving effect from any added rake. This effect is MAY be a tiny 2-3% difference, but my approach to performance is essentially by following the advice “pennies make dollars.”

I’m on a likely permanent break from building race quads. I got onto BMW’s prototype race team a few months ago. I quit yesterday because of a ton of grown men than can’t keep their panties straight, but I may get back to race quads one day. In the meantime, I’m going to keep focusing on asphalt racing.

The main reason is pretty simple. I’ve had dozens of conversations with pro riders from the ATV side, as well as pro riders and engineers from road racing. I can say something around the ATV crowd and get laughed at, but take those same ideas to asphalt and be told, “yeah, everybody knows that.” If I have to pick simply based on pedigree alone, I’m going to listen to an driver with an FIA Platinum license or a 30 year race engineer before I’m going to listen to a pro ATV rider that won’t believe a stop watch is a good indicator of lap times (true story).

Nonetheless, I’ll pop back here from time to time when I think of something relevant to the ATV side.

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DDQ get his shocks back for his new Tfaith frame yet?
You do Aarms for it too?
- DDQ 4 prez

He did send them out but they aren’t back yet.

I did the uppers but not lowers. I was in a huge rush at the time and didn’t have a lower arm design finalized.

Shit I didn’t even get to ride the thing lol

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  • 8 months later...

Figured I’d bring up some of the stuff that has been hitting my desk lately.

A chassis designed to use equal length arms to eliminate bump steer will in fact make it easy to eliminate bump steer, but you’re giving up everything that helps you maintain corner grip. On paper, I’m coming up with around a 20% loss in grip on average for the frames I have a model for. Some of them peak around a 40% loss in grip.

Bump steer is fine in some circumstances. I like no bump steer for the lower 80% of the travel and then a touch of bump in. This helps keep it straight on hard hits.

Everybody talks about straight line bump steer but nobody talks about when the bars are turned, which is a VASTLY more important matter. I’m getting close to trade secrets here but suffice it to say that eliminating bump steer while turning can cost you seconds. Not tenths. Seconds. Give the tire what it wants, not what Instagram hashtags tell you that it should want.

A year or two ago, I would have told you everything I know on the matter but after having another chassis builder tell me that I needed to come read this guide (ya know, the one I wrote) and learn a few things, I’m now aware that I’m helping an asshole. I have zero tolerance for rude people so if you want to know more about this, PM me or find me on facebook.

People like 250R rake (which is technically called wheel recession angle or WRA) but that comes at a cost. Higher WRA of around 15 degrees or so can cause a lot of dive under braking. Add in the extra weight of something that isn’t a 250R and the issue gets worse. If you can work with it then the extra comfort and compliance can be worth the trade off, but you have to work with it (weight on your feet under braking, not into your hands). There are about 6-7 things to look at with WRA but the gist is that heavier riders need less, heavier braking needs less, and a shorter wheelbase needs less.

For the 800th time, no wheel spacers ever.

The shock matters more than the arm.

With the shock, the spring has one job: to hold the load introduced to it. The valving controls how fast the spring gets back to its steady state when the load changes. If it’s rough as fuck, 95% of your issues are either because your tire pressure is off, your ride height is off, or your valving is off. It is VERY rarely the spring(s). If someone quotes hooke’s law (a sign they don’t know shit) then ask how that changes with velocity. Even if you don’t know the answer, it’ll let them know they’re at the end of their rope.

I’ll be back in about a month to bitch about something else.

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So curious, now you dont like the Fireball A-arms? 

I don’t have a problem with fireball. I don’t think their shock program is up to date, but it’s definitely not bad from what I’ve dealt with.

I do have a problem with occasionally wanting to rant about suspension when I have a little to drink and it’s quite possible that I did a shit job of saying something. Can you be more specific?

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