My son races small cars that are direct drive. An engine, engine gear, chain, and axel gear. Since there is no shifting finding the right gear ratio is critcial to the speed of the car. By examining the dyno reports on the engine and through trial and error you can determine the best gear ratio for the car. For example, a total drive train gear ratio would typically be 4.76:1. where the engine gear box is 6:1, the engine gear has 34 teeth and the axel gear has 27 teeth. However, there other ways to acheive the same ratio. for example with a 29 engine, 23 axel gear. Theoretically which option should provide the beter perfrormnce. The 29 gear will be smaller and lighter with lower moments of interia.. will such a drive train slow down faster and speed up faster? Same goes for the chain.. what is the impact of a lightweight chain.. Small differences in top speed (<10% ) are critical.