WOW, thank you very much guys, this forum really moves! ....... \
Well, the funny thing is that all my testing was done on regular 'loop' carpet, and I managed to get an average of 9.1 feet per second (150 feet test track), but in the competition, they had a velvety type of carpet (no loop), and my car was literally all over the place...and could barelly manage 8.4 feet/sec. (the winners did 9.8)
The setup of the car is made to be a bit 'loose' because of the nature of the competition (the robot follows a track, and you 're better off sliding the tail than pushing the front and loosing sight of the track); but at least the front/rear balance stays consistent.
Another factor is that I made the car really light, with carbon and all the fancy stuff so that my battery would last longer (I have a bunch of electronics going on); but it seems lighter is not better in carpet because you don't 'dig'...
Also, I didn't do any treatment on the tires, and I don't think the other guys did since their tires were plain rubber, as opposed to foam.(?)
anyway, I guess I'll have to purchase a couple of the tires you guys recommend here and try them out..
-Thanks again for now