Gear Ratios
A gear ratio is the number of teeth on the driven gear divided by the number of teeth on the driving gear. It tells you, in one number, how a gear pair changes rotational speed and torque as power passes through it.
01Definition
A gear ratio is the number of teeth on the driven gear divided by the number of teeth on the driving gear. It tells you, in one number, how a gear pair changes rotational speed and torque as power passes through it.
02Physical Principle
Mesh a small gear (the pinion) into a large one, and the large gear turns slower but with proportionally more torque — the same mechanical-advantage trade-off as a lever, delivered through interlocking teeth instead of a rigid bar. Reverse the pair and you get the opposite trade: speed instead of torque. A final drive on a bulldozer might use a ratio as steep as 6:1 specifically because the tracks need overwhelming torque at walking speed, never high speed at low torque.
03Mathematical Foundation
04Interactive Diagram — Gear Pair Simulator
Set the tooth count on the driving gear (A) and the driven gear (B) and watch the ratio, output speed, and torque multiplication update live.
Input speed fixed at 1,000 RPM on gear A.
05Interesting Facts
- Two meshed gears always spin in opposite directions — an odd number of gears in a train restores the original direction, an even number reverses it.
- A gear ratio doesn't have to come from a single pair: a gearbox chains several ratios together, multiplying them, to cover a huge range from one small engine.
- The teeth count, not the gear's physical size, is what sets the ratio — two gears of very different diameters but the same tooth pitch and count produce a 1:1 ratio.