Yes, the car must have an axle and wheels for it to be called a "car". The elastic system must be self-contained and I can't do something external like shooting the car with a rubber band from the outside. ============================================== Back to the problem of traction, I thought that CD's are great wheels because the contact surface is small and thus less friction (therefore can travel faster and further). If, indeed, more traction = better travel distance, wouldn't thicker wheels and wheels made of rubber be better than wheels thin like CDs? After all, why are CDs great wheels? Let's consider two examples of wheels that I found on a website: http://www.docfizzix.com/shop/supplies/s300df.shtml http://www.docfizzix.com/shop/supplies/s350df.shtml Which one would be more suitable for my project? (this 2 examples of wheels tackle the issue of traction) It seems to me that the second one (the high traction wheels) is only good for maximizing the speed but not the distance.......so high traction tends to decrease the travel distance???