if anyones interested heres a link to a uk website, with some videos you can download:
you need to register to download them, but its free.in the BRCA 1:10 rubber A-main, race a G4 took tq and the win! (national race series on rubber tyres)
theres also some other videos of foam races.
tooned: the plastic shims adjust the castor angle, which basically changes how much tyre is in contact when you apply steering lock.
to see this, take all the shims off, put the car on a flat board(with tyres on!) put the steering on full lock, look level with the front tyre, and move the top wishbone forwards and backwards. this should show how the castor works!
hope it helps.