Why Use Overdrive Or Underdrive Diff Gears

We often use overdrive or underdrive diff gears on the RC crawlers, but what do they really mean? Let's try understanding the pros and cons of a transmission with different gear ratios in the two axles and how to achieve them.

Why use an overdrive gear on the front axle

If the front and rear axles use the same speed differential gear, when the vehicle is moving straight, the front and rear wheels will travel at the same speed, but when turning, the distance the front wheels travel forward is reduced, but the speed of the rear wheels remains unchanged, so the rear wheels will push the front wheels. By using an overdrive gear on the front axle, the average speed of the front wheels is higher than the average speed of the rear wheels, which can effectively solve this problem.
The front wheel overdrive helps the front wheels pull the car up slopes and over obstacles instead of being pushed by the rear axle.

Pros
Front wheel overdrive helps the front wheels pull the vehicle up slopes and over obstacles instead of being pushed by the rear axle.
Front wheel overdrive helps the vehicle turn or climb up slopes and over obstacles because the average speed of the front wheels is higher than the rear wheels.
Good traction when turning on mud or sand.

Cons
On soft or muddy ground, the model may get stuck in the mud or sink, especially when using straight wheel driving.
On terrain with good grip, the front wheels will pull the rear wheels, putting stress on the transmission and increasing battery consumption.