If you want to do a gravity racer at your school you need two sets of wheels that contain two on each, a block of wood; with the wood you cut into the shape you want it to be, then you paint it. To start a race you have to be under the weight limit. The weight limit is 300g. You do not race against other schools you only race against your own school. You can have any kind of shape you want. They measure your distance, your time to get off the ramp and, last but not least, how long you glide. Hint: don't make your car too light and not too heavy.