Tuning guide for a stable A800R/RR

Tip 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:

  1. 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.

  2. 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.

  3. 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.

Tip 2: A MELLOW FRONT END

Two ideas to try if you're struggling with stability:
  1. Longer links at the front ! You can use the AM19-LTL bulkheads clamps at the front of the car. The upper arm / camber links will be 1mm longer. The result is a reduced camber gain and a front end that washes off a bit more. The front end hooks less into the track and settles after the rear, giving you a more reassuring car. You can go even further with this idea of having shorter rear upper arms vs the front. But instead of using the AM19-LTL at the front, you can use the short links position of the AM19-2 (or AM19-FX) at the rear and the stock AM19-R at the front. This gives you an even more dramatic difference between the rear and the front. The result is a rear end that settles super early in the corner, giving you a very reassuring car.

  2. Experiment with the ackerman setting. Usually the forward setting is for asphalt and the backward setting is used on carpet. Many driver don't bother and just set it in the middle all year round. But it's a powerful setting to fine tune your front end, it dictates how round or how aggressive is your overall corner shape. The most forward setting gives a rounder corner. Sometimes you'll be faster with a car that turns "square" than a nice round car. That's just the way it it, uglier but faster. This one is very tied to driver preference and how you like to approach corners.

  3. Reduce your steering angle ! This one is known from year 1 into your RC journey but in the heat of the moment you can sometimes forget about it. There is no trophy for who can run the most steering lock, your lap times are the final arbiter. If you're faster with reduced steering so be it. Usual values are 26deg (inside wheel angle) on asphalt and 24deg on carpet. Those are on the high side, reduce until you feel like your driving and not managing your car.

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