I had bought one of these micro racers when they first came out on the market, for like $25, and it came with chrome wheels. I believe they're exactly like the ones on the car now, except they're chrome. Anyway, the car took a crap after I abused the hell out of it so I'm using it for spare parts now.
Radio Shack sells an upgrade package for their cars which includes two sets of wheels/tires and motors/gears. You would have to take your car in to see if they fit. Hell, I'm gonna do that after work.