Polish the nails that the wheels ride on and the hole in the wheels. It gives you just a little less friction. And don't forget lots of graphite dust. We had the best results hollowing out the bottom and attaching the weights there. Be sure that the weights don't stick out or they will drag on the track. The further towards the back the better. Low in front and higher in the back like the indy cars gives the least drag. Good luck! No matter what, if your son does most of the work he will appreciate it more. You can tell the cars where the dads do all the work, and the kids couldn't care less about the whole thing. After the derby, we would make display stands for their cars. They still have them after all these years!