Suspension Optimization and Tuning Help

[Ron Sutton]

Hi Tyler,

I've been busy with client design projects the last few weeks & next week too. I'll see if I can carve out some time this weekend to map out your front suspension. But I have reviewed & analyzed your suspension issues.

I have some observations about Your Scout's handling characteristics that are clear from watching the videos. Thanks for those by the way. As Lance will tell you ... I am very visual ... and need photos and/or videos. I've spent 35 years watching race cars, roll angle, travels & tire angles.

From your videos, it is clear ...
a. Your Scout has too much roll angle for the camber you're running.
-OR-
b. You need more camber for the roll angle you're running.

c. Your front geometry only provides a moderate amount of camber gain in full dive. Not enough for the high roll angle you're running. So your outside front tire does not have a good contact patch when turning. In fact, when you turn the steering hard & fast, the contact patch narrows immediately. I am estimating about 40-45% contact patch loss. So your outside front tire is going from 11.5" of contact patch ... to 6". Since the rear tires still have a 12.5" contact patch (or close to it) ... the truck goes into an instant push.

d. The inside front tire has a decent contact patch because ... the inside wheel is losing camber as it lifts ... due to the high roll angle ... which is actually helping it. Often guys have optimized the camber for the outside front tire and have the inside tire working poorly. Your situation is the opposite.

e. You have a soft spring package which is letting the truck suspension travel a lot. That part I like, but you don't have a happy suspension package.



f. You have a high degree of roll angle from a combination of weight, higher CG and insufficient sway bar size.

g. You have a slight mismatch in front & rear roll angles. Ideally we want the front roll angle to be .3° to .4° less roll angle than the rear. This creates a balanced handling competition vehicle that is disengaging the inside rear tire more than the inside front tire. Yours is off a little. It is rolling slightly less in the rear than the front ... I'd say around .2° more in the front ... which is about .5°-.6° from ideal. What this does is keeps the inside rear tire too engaged ... and unloads the inside front tire to a higher degree ... contributing to your push condition.

h. The final ... but BIG issue, is your front shock valving doesn't have enough low-speed rebound. Meaning the front shocks let the inside front suspension roll too much and come up too quick when you step off the brakes. Ideally for AutoX & road courses, you need the shock valving to "tie down" the front end down through the roll through zone. And when the shocks do "let go" and let the front come up, it needs to happen slower. Otherwise it unloads the inside front tire ... adding to the push condition. You're probably running the shock rebound valving soft for more exit grip, but there are other, better ways of getting exit grip without killing the middle of the corner with a push.

So, before we get into changing roll centers, camber, caster, etc ... you need to pick a path for your suspension strategy. There are two good routes to go. And each strategy will need a different roll center and have different needs for optimum geometry.

#1 is a conventional low front travel/high roll angle set-up. You already have the high roll angle. For this, you would need stiffer front spring rates, reduce the compression travel on dive & keep the soft sway bars. Then you'll need to increase the camber gain & caster in the front geometry to work well with the higher roll angle.

#2 is a modern high front travel/low roll angle set-up. You already have the high front travel. For this, you would need bigger, meaner, stiffer sway bars, reduce the roll angle from the estimated 3° to around 1.5°. Then you "may" need to increase the camber gain & caster in the front geometry ... but not by much. When you roll the truck 1.5° less ... that's adds 1.5° dynamic camber to the outside tire. You will still want to optimize the camber & caster settings, but it won't need as big of a change as it needs with the high roll angle you have now.

Each has its pros & cons. If you're not clear on them, I'll be happy to provide insight. But if you're clear, pick a path and let's work on the whole suspension package along with the roll center & front suspension geometry.