Look at the close-up of the axle to see that the “gear” is made from a narrow strip of double-sided tape wound around the axle until the right diameter (gearing) was achieved through trial and error doing test runs down a track. The “gear” is glued on it’s sides to the axle with PL Premium The diameter of the gear is crucial to performance: too small and gearing will be too tall and acceleration off the line is too slow; too large and power to the rear wheels is so great that the wheels either lose traction and spin, or the car wheelies off to a start and falls over backward. Fast acceleration off the line is the trick to best performance down the track, so additional weights were added to the car to improve traction of rear wheels to the track, and to keep the front end down (avoid wheelies even though they look cool). Two 2 ounce pyramid shaped weights are placed as far back as possible and above the rear wheels – these help get power to the ground, without wheel spin. Their shape helps reduce air resistance. Another 2 ounce flat weight is added to the front end of the car, cantilevered out tot he front getting the weight as far forward as possible to help avoid wheelying. It also raises the contact point to starting gate as high as possible (see theory in BitMobile description).