http://www.oople.com/forums/showthread.php?t=119914
Here you go swell a whole thread on the discussion at club level seems to be an advantage for the 4wd racers; personally I run 2wd and have tried foams but couldn't see a great benefit cost wise as I'm a crap racer was forever knocking chunks off the fronts but you do seem to enjoy better grip levels I've since gone back to using rubber
but my lad still swears by his foams.