Torque Multiplication: How Gear Reductions Magnify Engine Force

A primary purpose of a transmission is to multiply the engine's torque. While an engine produces a specific amount of rotational force, this force is often insufficient to accelerate a vehicle from a standstill without gear reduction.

The Conservation of Energy

According to the laws of physics, a gear reduction reduces speed and multiplies torque proportionally. The output torque is calculated by multiplying the input torque by the gear ratio, factoring in mechanical efficiency:

$$\text{Output Torque} = \text{Input Torque} \times \text{Gear Ratio} \times \text{Efficiency}$$

For example, if an engine produces 200 lb-ft of torque, and the first gear ratio is 3.00, the output torque is multiplied to 600 lb-ft (minus small friction losses), helping the vehicle accelerate easily.

Calculate torque multiplication factors using our automotive gear ratio calculator. To convert engine RPM to vehicle speed, check out our guide on engine RPM to vehicle speed formulas.