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Gear Inches

Learn about the customary gearing system still in use today

Older standards are still used in the cycling industry. This article aims to explain what gear inches are, how they're calculated, and when they're useful.

What are gear inches?

Gear inches is the diameter in inches of the drive wheel of a high-wheel bicycle with equivalent gearing. It was originally intended for direct-driven bicycles, but has since been modified for the chain-driven "safety" bicycle.

How are gear inches calculated?

This system is less cumbersome to calculate than the development meter system. It's measured in inches and can be calculated by multiplying the diameter of the rear wheel by the gear ratio.

Gear inches can be calculated from the following formula, where TT stands for tire thickness, RD for rim diameter, GR for gear ratio, and GI for gear inches.

(TT × 2 + RD) × GR = GI

Where can measurements be found?

The thickness of the tire is measured across its tread, and the diameter of the rim is measured up to its bead. Both are measured in inches. A marking can also be found printed on the sidewalls of the tire. To learn more about tire sizes, please visit our articles covering the individual sizing systems.

When should gear inches be used?

Gear inches are most commonly used in countries that have not yet adopted the metric system. They're useful when the wheel sizes differ, however they're less effective when the crank arms are of different lengths. It's recommended to use gear inches prior to changing the tire width or rim diameter.

Which other gearing systems exist?

There exists several other systems, each with their advantages and drawbacks. To learn more about these gearing systems, please visit our articles covering each topic individually.

Why does BikeCalc provide all gearing systems?

BikeCalc tries to cater for all cyclists and modern bicycles. We realize that no system is better than an other, only some are better suited in certain circumstances; and it's up to the end-user to decide which one is most appropriate for their specific use case.