XRAY - Model racing cars

The T2 setup manual clearly explains how to change the roll centres and the effects and pros/cons of doing so. But it does not discuss the selection or combination of the elements to use to achieve the change, eg lower arm or camber link, or both. If camber link, raise outer point or lower inner point, or both. Lengthen/shorten camber link. Mix all that up with the quick settings. It cannot all be *** :-) *** it and see, must be some science/guidelines there.

Apologies if this has been discussed before but is there a paper or URL that will shed some more light on this?

Well, the only way to truly understand it is to look at each change seperately.

If you raise the top link keeping the length and angle the same (i.e. raise both inner and outer mounting) you actually lower the roll center (slightly). Everything that is described for lowering the roll center applies. In addition you also (very) slightly reduce camber change, but that effect is negligable.

If you shorten the top link keeping the angle and height the same you only increase the camber change. There is no change in roll center. Increased camber change means that as that side of the suspension is compressed, the top of the tyre is pulled inwards to make a bigger angle compared to the chassis. During cornering, if well setup, this means the tyre will stay at a 90 degree angle with the track surface maximizing the tyre's contact patch and thus grip.

Note that if you change the roll center by changing the lower arm position you also increase or decrease the camber change just like changing the angle of the top link does.

I'll leave it to you to work out what the effect of a combination of changes would have as there are a lot of different combinations . But to help you these are some guidelines I have set for myself:

- When you change the angle of the top link use shims on the outside mounting
- Use the inside mounting I only change to either raise/lower the top link (i.e. in combination with the outside mounting) or to change the length.
- If I want a big roll center change I change the angle of the lower arm then use the angle of the upper arm to fine tune the roll center and the camber change (the latter is usually the most important to get right).

Hope this helps.