How to Find the Gear Ratio on a Bike

Gear ratios depend on the size sprocket and chainring

Calculating bike gear ratios is a mathematical process for determining the ease or difficulty of a particular gear combination. A bicycle with multiple gears will have multiple ratios, each ratio determined by the particular combination of front and rear gear. Competitive cyclists sometimes use gear ratios to determine the ideal gearing for a particular race. In general, a larger gear ratio means a larger gear combination; the bike will travel further per pedal stroke, but the cyclist will need to exert greater effort to turn the gear.

Instructions

1. Determine the number of teeth on each of the sprockets at the rear of your bike. Bikes in 2010 can contain anywhere from 1 to 11 sprockets. The number of sprocket teeth is often stamped on the individual sprocket. If there is no stamp, you will need to count the teeth on each sprocket. A 13T sprocket, for instance, contains 13 teeth.

2. Determine the number of teeth on each front chainring. Your bicycle will have from 1 to 3 chainrings. Once again the number of teeth may be stamped on the chainring. If not, count the teeth on each chainring and note the results.

3. Calculate each gear ratio. The ratio is determined by dividing the number of teeth on the chainring by the number of teeth on a rear sprocket. For instance, a gear combination of 53/13T (a 53 tooth chainring/13 tooth sprocket) results in a gear ratio of 4.07 to 1. The sprocket spins 4.07 times to every revolution of the chainring. In other words, with each pedal stroke, your wheels turn 4.07 times.

References

• "Bicycle Maintenance & Repair for Road and Mountain Bikes;" 2005; Todd Downs

Resources

• Read this Article in Spanish
• SheldonBrown: Gear Theory