Cycling Gear Inch Converter

Understanding Bicycle Gear Measurements

Bicycle gearing determines how far you travel per pedal revolution and how much effort each pedal stroke requires. Three different metrics help cyclists compare gearing across different wheel sizes and drivetrain configurations: gear inches, gain ratio, and development (meters of travel). Each provides a slightly different perspective on the same fundamental question of mechanical advantage.

Gear Inches:

Gear inches represent the effective wheel diameter if you were riding a direct-drive penny-farthing bicycle. It was invented in the 1890s to compare the new chain-driven safety bicycles with the older high-wheelers.

Gear inches = (Chainring teeth / Cog teeth) × Wheel diameter (inches)

For a standard 700c road wheel (approximately 26.3 inches with a 23mm tire): Gear inches = (Chainring / Cog) × 26.3

Gain Ratio:

Gain ratio, proposed by Sheldon Brown, is a dimensionless number that accounts for crank length and is independent of wheel size. It represents the distance traveled per unit of distance the pedal moves.

Gain ratio = (Chainring / Cog) × (Wheel radius / Crank length)

On a road bike, gain ratios run from about 2.4 in the climbing gear to 8.8 at the top. A modern mountain bike with a 10-51 cassette drops to about 1.3 at the bottom, which is why it will climb things a road bike cannot.

Development (Meters of Travel):

Development is the distance the bicycle travels per complete pedal revolution, measured in meters. This is the most intuitive metric for many cyclists.

Development (m) = (Chainring / Cog) × Wheel circumference (m) Development (m) = (Chainring / Cog) × Wheel diameter (m) × π

Common Wheel Diameters:

Circumference here is π times the diameter, which is what the calculator uses. A loaded tyre squashes slightly, so a rolled-out measurement on your own bike will come in a few millimetres under.

Practical Examples:

• A road bike with 50/34 chainrings and 11-28 cassette on 700c×25mm wheels (671 mm):
  • Highest gear (50/11): 120.1 gear inches, 9.58 m development
  • Lowest gear (34/28): 32.1 gear inches, 2.56 m development
• A mountain bike with 32T chainring and 10-51 cassette on 29" wheels (739 mm):
  • Highest gear (32/10): 93.1 gear inches, 7.43 m development
  • Lowest gear (32/51): 18.3 gear inches, 1.46 m development

Gear Inch Ranges:

Tips:

• Lower gear inches = easier pedaling (good for climbing). Higher gear inches = harder pedaling (good for speed on flat terrain).
• A well-designed gear range covers from about 20 to 110 gear inches for all-around riding.
• When comparing different wheel sizes, use gain ratio or development rather than gear inches for more accurate comparison.