The bike gearing calculator is an essential tool for cyclists, allowing you to determine the ideal combination of chainring teeth, cog teeth, and wheel size to optimize your riding efficiency and desired speed. Find your perfect gear ratio for racing, touring, or commuting.
Bike Gearing Calculator
Your Calculated Speed is:
Gear Ratio: — | Gear Inches: —
Detailed Calculation Steps
- Enter values and click Calculate to see steps.
Bike Gearing Calculator Formula
Variables
The calculation uses four primary variables:
- Chainring Teeth (CR): The number of teeth on the front sprocket (crankset).
- Cog Teeth (CG): The number of teeth on the rear sprocket (cassette).
- Wheel Diameter (WD): The overall diameter of the wheel (rim + tire) in inches. Common values are 26, 27.5, or 29 inches.
- Cadence (CAD): The rate at which the rider pedals, measured in Revolutions Per Minute (RPM).
What is a Bike Gearing Calculator?
A Bike Gearing Calculator is a fundamental utility for cyclists to determine the mechanical advantage (gear ratio) and resulting output metrics, primarily Gear Inches and Speed, for any specific gear combination on a bicycle. Gear Inches represent the distance a bicycle travels for one full revolution of the crank, measured in the equivalent diameter of a high-wheel penny-farthing bicycle.
Understanding these values is crucial for optimizing performance. A high Gear Inch value (e.g., 90+) is suitable for high speeds on flat terrain or downhill, requiring more effort per pedal stroke. A low Gear Inch value (e.g., 30-) is better for climbing steep hills, requiring less effort but more pedal strokes (higher cadence).
By calculating the exact speed for a given cadence, riders can select the gearing that best matches their power output and the terrain, ensuring they maintain an efficient and comfortable pedaling rhythm (cadence) regardless of speed.
How to Calculate Bike Gearing (Example)
- Define Inputs: Assume a setup with a 50-tooth Chainring (CR=50), a 15-tooth Cog (CG=15), a 27-inch Wheel Diameter (WD=27), and a rider cadence of 80 RPM (CAD=80).
- Calculate Gear Ratio: Divide the chainring teeth by the cog teeth. $$ \text{Gear Ratio} = 50 \div 15 \approx 3.333 $$
- Calculate Gear Inches: Multiply the Gear Ratio by the Wheel Diameter. $$ \text{Gear Inches} = 3.333 \times 27 \approx 90.0 \text{ in} $$
- Calculate Speed (MPH): Multiply Gear Inches by Cadence and the constant conversion factor (approx. 0.002975). $$ \text{Speed (MPH)} = 90.0 \times 80 \times 0.002975 \approx 21.42 \text{ MPH} $$
Frequently Asked Questions (FAQ)
What is the ideal cadence for cycling?
Most professional and experienced cyclists aim for a cadence between 80 to 100 RPM. However, the ideal cadence is personal and depends on the rider’s fitness, the terrain, and the type of cycling (e.g., time trials favor higher cadences).
What is the difference between Gear Ratio and Gear Inches?
Gear Ratio (GR) is a unitless number showing the mechanical advantage (how many times the wheel turns for one crank rotation). Gear Inches (GI) is a distance measurement that combines the GR with the wheel size, giving a practical measure of the effort required for propulsion.
Why is my wheel diameter not exactly the stated size (e.g., 29 inches)?
The nominal size (e.g., 29″) is a rough approximation. The actual wheel diameter depends on the tire’s width, profile, and air pressure. For highly precise calculations, you should measure the wheel’s circumference and divide by $\pi$ to get the exact diameter.
How do I use this calculator for metric units?
To calculate Rollout in meters, you must input the wheel circumference in meters. For speed in Kilometers Per Hour (KPH), you can use the calculated Gear Inches and convert the final result: $\text{KPH} = \text{MPH} \times 1.60934$.