Also a transmission has to be designed correctly. On the one hand, this is the right choice with regard to the transmission ratio of the individual gears as well as the determination of the best functioning primary gear ratio.
The decisive factor is the applicable power, the total weight of the driver with the vehicle and the acceleration or final speed to be achieved or desired. All this can only be estimated before engine mounting. Often one is in the selection of the translation next to it and complains gear connection and / or too little final speed.