Crank arm length is often overlooked on a bicycle. This article aims to explain what gain ratios are, how they're calculated, and when they should be used.

### What are gain ratios?

Gain ratio is the ratio of the distance of pedal travel to the distance of wheel travel. It was orignally proposed by Sheldon Brown and has since gained traction as a more universal system to designate gearing of bicycles.

### How are gain ratios calculated?

This system is the most demanding to calculate, but thanks to Deraileur it has become easier than ever before. It's expressed as a ratio and thus any measurement units may be used, as long as the same is used for measuring the wheel radius and crank arm length.

Gain ratios can be calculated from the following formula, where TT stands for tyre thickness, WR for wheel radius, CAL for crank arm length, and GR for gear ratio.

(TT + WR) / CAL × GR

### Where can measurements be found?

The thickness of the tyre is measured across the tread, and the diameter of the rim is measured up to the rim bead, then divided by two to get the radius. A marking can also be found printed on the sidewalls of the tyre. To learn more about tyre sizes, please visit our articles covering the individual sizing systems.

The length of the crank arm is measured from the center of the bottom bracket to the center of a pedal. There should also be a marking found engraved on the interior of the arms.

### When should gain ratios be used?

Gain ratio is the most versatile system when it comes to comparing gearing on bicycles. It takes into equation different tyre widths, rim diameters, and crank arm lengths. It's recommended to use gain ratios prior to changing the wheel size or crank arm length.

### Which other gearing systems exist? 