Suspension Setup and race tuning

[tfaith08]

Loco, if you’d like to sticky this then it may help. The suspension guide is getting somewhat long and this pertains to just setup and testing.

 

Setting suspension up is pretty much what the off-road side calls a setup package from other types of racing. Every setting change to any adjustable item on the quad that doesn’t fall into making power is a part of the setup. It is assumed that you’ve already fully assembled the quad and it is ready to ride, to include fuel and anything you intend to bring on a ride (coolers, extra lights, etc.).

 

These will be in order. If you skip any step, good luck.

 

Find a level surface. Use a 4’ level (or 6’ if needed) and use something as shims to create 4 level spots for the tires to sit on. “Within the lines” on the level is half-ass, take the time to get to dead center. You’ll also want a 5th and 6th surface to measure ride height. The 5th will be under the frame rails at the foot pegs, and the 6th forward of the foot pegs and on the lower frame rails just before they sweep up for the front suspension. These also need to be level with the 4 corners. Make sure to make it somewhat durable since you’ll need to bounce the quad and get the suspension to settle.

 

Set tire pressure equal for each side. FL and FR should match as should RL and RR, but not necessarily matched F/R. Enough to keep the tires from rolling under the rim in a hard corner is about all you need.

 

Ratchet strap the stem straight. Use the stem flag as a reference. The stem may be bent which rules out using the handlebars as a reference. The setup may currently be off so that rules out everything else. Once the stem flag is straight, measure how straight the bars are. If they’re off, replace the stem or fix it.

 

Next is to determine ride height. This ranges from 5” to 8” depending on how you ride and where. I hate vet it is, set a target. If you don’t know then just choose 7-3/4 front and 7-1/4” rear.

 

From here, there are two avenues. The first is FAR more advisable.

 

1A. Sit on the quad and have someone measure the vertical distance from the ground to a static point on each tire/rim. The nut or top/bottom of the rim is acceptable. Write this number down.

 

1B. Remove the shocks and support the quad by placing blocks under the frame rails at the 5th and 6th level spots. Measure the same distance from 1A and find the difference. Depending on your weight, tire selection, and tire pressure, this may be 1/16-1/4” and youl have one for front and rear. Whatever they are, write them down and do not lose it. Call them height factors.

 

1C. Add the height factors to your ride heights. If your height factor is 3/16” and your ride height target is 7-1/2, your total block height would be 7-11/16.

 

1D. After everything else is finished, install the shocks and set the preload to get to ride height.

 

2. Sit on the quad and convince someone to pull every measurement from here on out. At every change, you need to bounce the quad a few times and slowly setting to your riding position with all of your gear and in your riding position WHILE RIDING FAST. The way you sit on it after starting it and the way you run through the fast stuff will absolutely be different.

 

Set your caster. With all frames without anti-dive (caster gain), your caster will only ever change with the pitch of the quad but never height. To my knowledge, only YFZ450Rs have this feature. Additionally, caster is typically calculated and rarely ever needs to be changed. 5 degrees is ballpark.

 

Set toe and camber. These play back and forth with each other. A change in one will affect the other in 100% of cases. Therefore, if you want more camber, you’ll need to go back and take toe out of it to keep it the same.

 

I will add a part 2 for testing.

 

 

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[ClaudeMachining]

For the record : I like goats.

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[tfaith08]

This is assuming you have fully adjustable suspension and arms.

Caster: if the bars don’t want to self-center at speed and in chattery sections, add more caster. Do not go below the calculated minimum mentioned above.

Tire pressure: If the tires want to roll under the rim, add pressure. If you can’t find a way to soften excessive small chatter or you just cannot get the grip out of them, lower pressure. You have to find a balance between compliance (grip) and how much load the tire can take.

To make matters worse, more grip creates more load, requiring a higher pressure. Dive into internalizing it and picturing it all you’d like, but the major takeaway is that any fold under requires more pressure. If it happens once or twice, no big deal. If it happens consistently, fix it. The suspension should never have a greater load capacity than the tires. If it does, you’ll hit the rim or the tire will roll under.

Toe: affects turn in speed and maximum cornering force. Since the tire isn’t a rigid entity, care has to be taken to factor what the tire contact patch is doing instead of where the rim is pointed. The difference between the direction the tire is pointed and the direction the contact patch is pointed is called the tire slip angle. Less pressure creates a greater maximum slip angle but there is a point of diminishing return where you have too much slip angle to sort out with toe. Toe is almost exclusively there to counter slip angle. Since the outside tire sees a greater load than the inside, it will see a greater slip angle.

Some ackerman is fine, but too much slip angle means the outside contact patch is pointed far too little toward the turn vs the inside. This is why anti-ackerman exists; to point the contact patch where it needs to go no matter what the rest of the tire is doing.

A dragging inside tire helps rotate the quad but having the contact patches working together works better. If it feels like you can’t get the outside tire to do enough work, add toe or lower pressure. If it begins to walk unpredictably left and right in a straight line, toe in more. If it walks left and right predictably, reduce toe. If it walks toward bumps, toe in.

With camber, you want to aim to keep the tire pressing down on the contact patch that’s trying to fold under the rim. The minimum camber setting is derived from simulating full dynamic load, which is the absolute maximum load that one tire will see. To simulate it, fully compress the front end and turn full lock. If you turn left, cut the pressure in the front right tire to around 1/3 what you’d normally run, then support the rear left if needed. Adjust the camber to get around 1 degree on the front right. Once you’re done, set the quad back to ride height and check the camber. This number is your absolute minimum setting. As you change tire pressure, your minimum camber setting will change. Higher pressure will use less whereas lower pressure will need more camber.

Diagnostics:

With all of these, make small adjustments. It is assumed that you are riding properly in all of these scenarios (weight on the pegs and not the seat, transferring weight to the inside, etc.)

Corner entry oversteer without steering
-lower rear pressure
-increase front pressure
-raise front or lower rear
-reduce rear rebound
-increase front low speed compression
-increase front main spring rate

Corner entry oversteer with steering
-same as above but consider lower caster or lower front pressure

Mid corner oversteer
-lower rear pressure
-lower rear low speed compression
-reduce front rebound
-increase front main spring

Corner exit oversteer
-lower rear tire pressure
-reduce rear low speed compression
-lower rear ride height
-reduce front rebound

Corner entry understeer
-lower front pressure IF the tire isn’t folding. If it is, increase the pressure until it doesn’t.
-toe in
-reduce rear rebound
-reduce front low speed compression

Mid corner understeer
-lower front pressure IF the tire isn’t folding. If it is, increase the pressure until it doesn’t.
-if excess body roll, increase main spring rate or low speed compression. If not, lower it.
-faster rebound

Corner exit understeer shouldn’t typically exist with an ATV if you’ve rotated correctly in the corner. In my entire life, I’ve encountered one scenario where tuning fixed it whereas all of the rest involved riding technique changes.

Do NOT change all of these settings if you have an issue. If you have an issue, start with one change. If you have a few issues, pick one change that is common between the two. The ideal setup is one where there is a mild 4 wheel slide as the tires approach the limits of their traction and the quad slides evenly through the entire corner.

Aside from this, pitch, dive, and roll are mostly affected by slow speed compression whereas impacts and hits are affected by high speed compression. If you do something to transfer the weight from one side to the other (or front to rear, rear to front) and briefly lose traction, you need faster rebound on the end you’ve taken weight from. Additionally, going into a rough section can demonstrate a lot as well. If the shocks do fine for the first portion and then get progressively more stuff and bottom out, you need faster rebound. If the quad takes a hit and it bounces back up, you need slower rebound. These are what I categorize as the off-road aspects.

You have to balance the acts of cornering and the aspects of off-road terrain when testing and finding a good setup. Unfortunately, you’ll have to occasionally pick between one or the other. In all these scenarios, follow the priorities of safety, confidence, then lap times. Safety is #1 because if you die in turn 1, you lose every race from then on out. If you have to check up because you don’t trust the quad, you can’t push it enough to find what it can do. If you do trust the quad, chase performance.

KEEP A NOTEBOOK. Keep every note you can think of. You’ll wish you had once you lose.

Beyond that, memorize the racing line and trust your stopwatch.

With these things, you start getting into legitimate race engineering. This is the realm where it is assumed that the person riding is wholly competent to win a championship and the race engineer is responsible for all aspects of performance.

Don’t be surprised if it takes weeks of testing to find a good setup. Every setup package I deliver is always noted with bold text “initial setup.” Chad Wienen had a team of people with high speed cameras and trucks of tools and shocks when he was hard in testing. This is common. You may also make a change and it be the wrong change. This is also common. Even worse, you may make a change and it feel better but be slower.

If you skip steps in the setup, your testing will be all over the place and you’ll chase your tail.

Once you’re done, you go back and put it back on your setup pad from the first post and measure EVERYTHING. This is called a set down, which is just double checking where everything ended up. The added benefit is that if you have to adjust one side and not the other, it can indicate a bent chassis or suspension component.

Beyond that, be as objective as possible. You don’t have to follow all of these steps to get a safe setup, but you do if you want it to perform as well as you hoped it would when you dropped all the money for the parts.


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