A car's transmission typically serves two purposes - to change the gearing of the car and to allow the left and right wheels to move at different speeds, which is necessary for maximum grip in the corners (read about differentials.)
Because electric motors spin VERY fast, a transmission typically is necessary to reduce the gearing of the car, so that the wheels rotate fewer times than the motor, making the car drivable.
The difference in rotation between the transmission input (typically the shaft the spur gear is mounted on) and the driveshafts is referred to as the transmission ratio.
Most cars do not have many options in terms of types of transmissions, however, 2WD off-road cars do have some - they allow you to change the number of gears in the transmissions and the layout of their transmission.
Transmission Gears
Mostly applicable to 2WD 1/10 scale cars:
3-gear transmissions
- Less weight in rear
- More on-power steering
- Generally suited for high-grip conditions
4-gear transmissions
- More weight in rear
- More on-power traction in rear
- Generally suited for low-grip conditions
Transmission Orientation
Mostly applicable to 2WD 1/10 scale off-road cars:
Stand-up transmission case
- More rear traction
- Moves weight to rear of the car
- Generally suited for low-grip conditions
Laydown transmission case
- More on-power steering
- Moves weight forward
- Generally suited for high-grip conditions
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