Tuning guide for a stable A800R/RR
Tip n°1: ROLL CENTERS
If your car is too nervous and you can’t figure out why, there’s a good chance your roll centers are the culprit. Roll centers are adjusted by adding or removing washers under the lower arms and upper arms/camber links. Note that 1mm under the lower arm moves the roll center more than 1mm under the upper arm.
Fair warning: there are no magic numbers here. Finding speed is the slowest thing you’ll do all weekend. Roll center height is a thing that constantly changes, subject to driving style, preferences, conditions and even trends. The weird thing is that a high roll center setup and a low roll center setup can give identical lap times.
Three ideas to try if you’re struggling with stability:
Flatten your roll axis. Forget the usual « lower front roll center than rear » rule for a moment. Try having the same amount of washers under the front and rear lower arms. It usually reduces steering and gives you a calmer, more predictable car.
Check the angle of your upper arm / camber links compared to your lower arm. Usually we try to avoid having a camber link angled upward from the wheel to the car. This tends to make the car unpredictable. Try to have either parallel upper links / camber links to the lower arm or even angled downwards from the wheel to the car.
Experiment with different roll center heights. This one is the most time consuming but is necessary if you want to get 100% of the grip possible. Once you find a balance front to rear that you’re happy with, to further optimize, you can try shifting everything up or down by 1mm. That way, you will find if a high roll center philosophy better suits your conditions or driving style. One rule: whenever you move 1mm under the lower arm, mirror it on the inner side of the upper arm. That way you’re only changing roll center height, not camber gain
Those are general tips and not really set-in-stone values. If you look at the bulk of A800R/RR setups you will see widely different roll center philosophies, even at the same event sometimes. You can have as low as 0mm or as high as 3.5mm of shims under the lower arms. By iterating, testing and tracking what you feel and most importantly your lap times over a 5min session, you will get the roll centers setup right and you’ll end up with a car that’s both stable and fast.
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