http://www.rc-direct.co.uk/-c-39_198_205.html
these should do the trick.
1 doghnut will be enough to do one front and one rear. (on tenth buggy wheels)
I true them quite a lot and put a shape on them so they are rounded like normal buggy tires when you look at them head on.
It will go like its on rails.
If no jumps, try sticking some very soft touring car springs on at the front. I will be mental. You will prob need to make some spacers to fit them.
Hope that helps.