I am working on a vehicle. For this, I have to design a gear box which is to have some reduction ratio. Now the problem is I don't know how to do that. I know my engine specifications ( for example : Max net power: 5.38 KW (7.2 PS) @ 7500 rpm Max net torque: 7.66 Nm @ 5500 rpm) According to my calculations, total opposing force acting on vehicle is 344N and radius of rear wheel is 0.356m. Going by that, torque required at rear wheel is 122Nm. Now if we divide these two to torques (rear wheel to the engine), we get a reduction ratio of 16:1. But The reduction ratio in normal vehicle is less than equal to 10:1. that is why I am not convinced about my way of calculating reduction ratio. My vehicle is a 3 wheeler with total height of less than 0.6 meters and a total length of 3 meter. So Is reduction ratio affected by length of vehicle?