Use the bicycle gear speed calculator to determine your maximum or cruising speed based on your chainring size, cog size, wheel diameter, and pedaling cadence (RPM). This tool supports solving for any missing variable, provided four out of five values are known.
Bicycle Gear Speed Calculator
Bicycle Gear Speed Calculator Formula
$$ S_{km/h} = R_{RPM} \times \frac{T_c}{T_r} \times D_{mm} \times \frac{60 \times \pi}{1,000,000} $$
Where:
- $S$: Speed in kilometers per hour (km/h)
- $R$: Cadence in Revolutions Per Minute (RPM)
- $T_c$: Number of Teeth on the Crank (Chainring)
- $T_r$: Number of Teeth on the Cog (Cassette)
- $D$: Wheel Diameter in millimeters (mm)
Formula Source: Sheldon Brown’s Gear Calculator | Related Source: Bike Gremlin Gear Ratios
Variables Explained
- Crank Teeth ($T_c$): The number of teeth on the front chainring. This is the driving gear.
- Cog Teeth ($T_r$): The number of teeth on the rear cassette or cog. This is the driven gear.
- Wheel Diameter (D): The total measured diameter of the wheel and inflated tire, typically in millimeters (mm).
- Cadence (RPM): The rate at which the rider is pedaling, measured in pedal revolutions per minute.
- Speed (S): The final calculated speed, typically measured in kilometers per hour (km/h) or miles per hour (mph).
Related Calculators
- Bicycle Gear Ratio Calculator
- Pacing and Time Trial Estimator
- Cycling Power to Weight Ratio
- Optimal Tire Pressure Calculator
What is Bicycle Gear Speed Calculator?
A bicycle gear speed calculator is an essential tool for cyclists, engineers, and hobbyists used to quantify the relationship between mechanical input (pedaling cadence) and resulting speed. It provides a precise metric for understanding how gear selection impacts performance under various conditions.
The calculation is fundamentally based on three main components: the gear ratio (the ratio of teeth between the crank and the cog), the rollout distance (determined by the wheel diameter), and the time factor (cadence). By adjusting any of these inputs, a rider can immediately see the theoretical change in speed, which is crucial for planning optimal gearing setups for different terrains like hills or flats.
This calculator is often used by professional riders to compare the efficiency of different drivetrain setups and select the perfect combination of chainrings and cassette cogs to maintain their preferred cadence range (usually 85–100 RPM) while maximizing speed.
How to Calculate Bicycle Gear Speed (Example)
Assume the following parameters:
- Determine the Gear Ratio: The rider is using a 52-tooth chainring ($T_c$) and a 12-tooth cog ($T_r$). Gear Ratio = $52 / 12 = 4.333$.
- Input Physical Dimensions: The wheel diameter ($D$) with the tire is measured at $680$ mm.
- Measure Cadence: The rider maintains a cadence ($R$) of $95$ RPM.
- Apply the Formula: Use the formula $S = R \times (T_c / T_r) \times D \times K$, where $K = 0.000188495559$.
- Calculation: $S = 95 \times 4.333 \times 680 \times 0.000188495559 \approx 50.15$ km/h.
- Final Result: The theoretical speed of the rider in this gear is approximately $50.15$ km/h.
Frequently Asked Questions (FAQ)
What is a good cadence (RPM) for cycling?
For most recreational cyclists, a cadence between 80 and 90 RPM is comfortable. Competitive road cyclists often aim for 90 to 105 RPM, as a higher cadence is generally more efficient and reduces stress on the knees.
How does wheel diameter affect speed?
For a fixed gear ratio and cadence, a larger wheel diameter (e.g., 700c vs 650b) will result in a higher speed because the wheel covers a greater distance per revolution. This is a critical factor for riders who switch between different bike types (road, mountain, gravel).
Is this calculation for maximum speed only?
No. The calculation gives the theoretical speed for the specific cadence entered. If you enter your cruising cadence (e.g., 85 RPM), you get your cruising speed. If you enter your maximum sustainable cadence (e.g., 120 RPM), you get your potential maximum speed for that gear.
What is ‘Gear Inches’?
Gear Inches is an older unit often used to express the speed potential of a gear combination. It is calculated as $(\text{Crank Teeth} / \text{Cog Teeth}) \times \text{Wheel Diameter in Inches}$. While it is not a speed, it is directly proportional to speed for a given cadence.