How Gearing Affects Speed
Bicycle speed depends on the ratio between the front chainring and rear cog along with your pedaling cadence. A larger chainring or smaller rear cog results in higher speed for the same cadence. Wheel diameter also plays a role—the larger the wheel, the farther you travel per pedal stroke.
Many riders describe gearing in terms of gear inches, which is simply the wheel diameter multiplied by the gear ratio. A setup with 90 gear inches feels “harder” to push than one with 60 gear inches because each pedal revolution covers more ground. Comparing gear inches across bikes helps you understand how a compact road crank differs from a mountain bike granny gear.
Cadence is the other half of the equation. Recreational cyclists often spin at 60–80 RPM, while racers may maintain 90 RPM or more. A high cadence allows your muscles to work efficiently, but it also demands greater cardiovascular output. Thinking about cadence in advance makes it easier to choose gears that keep you in your preferred rhythm.
The Formula
The distance traveled for one crank revolution is the wheel circumference multiplied by the gear ratio:
where is wheel diameter, is chainring teeth, and is cog teeth. Speed is distance per minute multiplied by cadence:
To convert to kilometers per hour, multiply by 60. This calculator performs the math instantly so you can test different setups.
Using the Tool
Enter the number of teeth on your chainring and rear cog, your wheel diameter in meters, and your expected cadence in revolutions per minute. The calculator outputs your speed in kilometers per hour. Experiment with various gear combinations to find a comfortable balance between effort and velocity for climbs, sprints, or everyday rides.
If you are unsure of your wheel diameter, check the sidewall of your tire for the size (such as 700c or 26 in). Converting to meters ensures the formula delivers accurate results. You can also try multiple cadences to see how spinning faster or slower affects speed with the same gears.
Worked Example
Suppose you ride a road bike with a 50 tooth chainring and a 17 tooth rear cog on 0.7 m wheels while maintaining an 85 RPM cadence. Plugging these values into the calculator yields a speed of roughly 31 km/h. Switching to a 15 tooth cog increases the gear ratio and bumps speed to about 35 km/h at the same cadence.
| Chainring | Cog | Cadence | Speed |
|---|---|---|---|
| 50 | 19 | 85 RPM | 28 km/h |
| 50 | 17 | 85 RPM | 31 km/h |
| 50 | 15 | 85 RPM | 35 km/h |
More Than Numbers
Understanding the relationship between gear ratios and speed helps cyclists train efficiently. Higher cadences may reduce muscle strain but require cardiovascular endurance, while bigger gears create more resistance. Use this tool alongside real-world rides to fine-tune your shifting strategy and push toward your fitness goals.
When planning a route, consider more than mechanical advantage. Wind, road surface, and tire pressure all influence your achievable speed. A low gear that feels easy on a climb may spin out on a descent. Practice shifting before you need to change gears so transitions stay smooth.
For riders who track training data, pairing the calculator with a bike computer lets you compare theoretical speeds to actual ride logs. Noticing gaps between calculated and real-world speed can highlight technique issues like poor pedaling efficiency or excessive coasting.
Why Use a Gear Speed Calculator?
Gearing decisions influence how comfortably and efficiently you ride. Choosing too large a gear can sap energy and strain joints, while an overly small gear leaves you spinning without making progress. A gear speed calculator gives cyclists a preview of how different combinations feel before hitting the road. Commuters can plan gear choices for hills on their route, while racers can map out gearing for criteriums versus long climbs. By seeing the relationship between cadence and speed, you can maintain a training zone that builds endurance without overexertion.
The tool is particularly helpful when shopping for a new bike or drivetrain. Manufacturers often list gear ranges, but translating “50/34 chainset with 11-32 cassette” into everyday speed takes mental gymnastics. Plugging numbers into the calculator clarifies whether a compact or standard crank better suits your terrain and fitness. Riders experimenting with single-speed setups can also use the calculator to ensure their chosen ratio suits both climbs and descents.
Expanded Worked Example
Imagine preparing for a charity ride with rolling hills. You use a 48 tooth chainring, a 16 tooth cog, 0.7 m wheels and expect to pedal at 90 RPM on flats. The calculator shows a speed of about 30 km/h. On a steep climb you might switch to a 34 tooth chainring and 28 tooth cog. Keeping cadence at 80 RPM drops speed to roughly 18 km/h, yet the lower gear prevents muscle fatigue. Seeing these numbers ahead of time lets you plan pacing, nutrition, and drafting strategies.
The MathML expression summarizes the calculation: circumference times gear ratio times cadence, converted to kilometers per hour. Each factor provides a lever you can adjust depending on terrain and fitness.
Comparison Table
Use the table below to compare common gear setups at 90 RPM. Speeds are rounded.
| Chainring | Cog | Wheel (m) | Speed (km/h) |
|---|---|---|---|
| 50 | 17 | 0.7 | 32 |
| 46 | 16 | 0.7 | 30 |
| 34 | 28 | 0.7 | 18 |
The comparison illustrates why touring bikes often feature small chainrings and large cogs—they trade top speed for the ability to climb with heavy loads. Road racers reverse the strategy, opting for tighter clusters that keep cadence steady during sprints.
Limitations and Assumptions
The calculator models speed on a perfectly efficient drivetrain and assumes no tire slip. Real-world performance depends on aerodynamic drag, tire pressure, slope, and wind. Cadence also fluctuates during rides; the value you enter is an average. Treat the result as a baseline estimate and cross-check with a cycling computer to account for environmental factors. Additionally, make sure wheel diameter matches the outside diameter of the tire, not just the rim size, to avoid underestimating or overestimating distance per revolution.
Despite these caveats, the calculator offers a solid starting point for understanding how mechanical choices translate into road speed. Combining its output with ride data and perceived exertion helps you refine training plans and gear selections over time.