XRAY - Model racing cars

if i move rear arms forward i 'll have more or less grip?

same to front

More grip; bear in mind also that shortening the wheel base enhances rotation, particulalry useful for short tight tracks but reduces stability which is less helpful on larger tracks especially with fast sweepers.

As it happens, having reduced our wheelbase to 255, I have just changed it to 256 and may even take it to 257 (ie lengthening the front) as we are finding that 255 makes it just too difficult to control the rear unless the track grip is really good.

but also remember if you alter the length of the front you alter the Ackerman too

If you change front wheelbase, you also change your ackermann effect of the steering. This effect is very strong and usually in a different direction. If you only want to shorten the wheelbase, you should also remove a shim at the inner steering linkage.

shorter front wheelbase -> more weight on the front axle, usually less steering
shorter rear wheelbase -> more weight on the rear axle, usually more steering
(except asphalt with sugarwater or hot weather)

this effect is stronger than making front and rear shorter by the same amount

If you mix it with the ackermann change that you get by not adjusting the inner shims when you change wheelbase, you will feel mostly the change in ackermann and be confused

This is BTW one advantage of the '11 over the '10 car, because you can compensate the change in wheelbase exactly at the steering link.

I seem to recall that moving the rear arms forward will give more rear grip but will break away more violently when it does go.

I think this is provided there is enough grip in the first place.

Skiddins

On carpet it is easy and as described.

On Asphalt it depends on temperature and grip. But you are right, the "more steering"-effect comes in play at or close to the limit. Ideally this is where you should be most of the time

so longer rear wheelbase gives more rear traction ?

no,beacuse you are farther to the CG so weight is going to the rear axle slower
if you ve got more weight on any axle you ve more grip
in r/c set up almost everything is about weight transfer

"more rotation" is often used synonym for "less rear grip" or "more front grip" which feel nearly the same on the track...

If your wheelbase is 257 or 259mm is often not so much difference.

Try 258mm with short front and long front (with compensated Ackermann as described above, so make sure that you begin with a Ackermann setting that you can modify in the desired direction) and 257 and 259mm with the same front, and you will see that the weight change (having both axles more to the front or more to the rear) does a lot more difference than the actual wheelbase.

I like this kind of tests very much, although they use a good part of a practice day and it is a lot of work to do, you can always learn a lot...


David