This calculator determines the Gear Ratio (GR) and Gear Inches (GI) for any bicycle drivetrain setup. Understanding your gear ratio is crucial for optimizing speed, cadence, and hill-climbing ability, ensuring you have the right setup for your riding style.
Bike Gear Ratio Calculator
Bike Gear Ratio Formula
Gear Ratio (GR) = Front Chainring Teeth / Rear Cog Teeth
$$ GR = \frac{F}{R} $$
Gear Inches (GI) = Gear Ratio \(\times\) Wheel Diameter
$$ GI = GR \times D $$
Variables
- Front Chainring Teeth (F): The number of teeth on the chainring attached to the crank arms (e.g., 50T or 34T).
- Rear Cog Teeth (R): The number of teeth on the rear cassette or freewheel cog currently in use (e.g., 11T or 28T).
- Wheel Diameter (D, in inches): The effective diameter of the wheel and tire combination, typically ranging from 26 to 29 inches.
Related Calculators
- Bicycle Cadence to Speed Converter
- Tire Size to Wheel Diameter Calculator
- Cycling Power to Speed Estimator
- Chain Length Estimator
What is Bike Gear Ratio?
The Bike Gear Ratio is a fundamental metric in cycling that quantifies the mechanical relationship between your front chainring and your rear cog. It is calculated by simply dividing the number of teeth on the front chainring by the number of teeth on the rear cog ($$ GR = F/R $$). A higher ratio (e.g., 4.5) indicates a “harder” gear, meaning the wheel turns many times for each crank revolution, suited for high-speed flat riding or downhills.
Conversely, a lower ratio (e.g., 1.0 or less) indicates an “easier” gear, where the wheel turns fewer times, requiring less effort to push the pedals, which is essential for climbing steep hills or accelerating from a stop. The Gear Ratio itself is unitless, only providing a multiplier of wheel rotation relative to crank rotation.
Gear Inches (GI) provides a more tangible value by multiplying the Gear Ratio by the wheel’s diameter. It represents the diameter of a wheel that would travel the same distance in one crank revolution if it were directly driven (like a Penny Farthing). Gear Inches are the most effective way to compare the gearing of bikes with different wheel sizes (e.g., 26-inch mountain bikes vs. 700c road bikes).
How to Calculate Bike Gear Ratio (Example)
Suppose a cyclist is using a 52-tooth chainring, a 15-tooth rear cog, and has wheels with an effective diameter of 27 inches.
- Determine Gear Ratio (GR): Divide the Front Teeth (52) by the Rear Teeth (15). $$ GR = \frac{52}{15} \approx 3.467 $$
- Determine Gear Inches (GI): Multiply the Gear Ratio (3.467) by the Wheel Diameter (27 inches). $$ GI = 3.467 \times 27 \approx 93.61 \text{ inches} $$
- Interpret the Result: The resulting Gear Ratio of 3.47 means the wheel rotates 3.47 times for every one rotation of the pedals. The Gear Inches of 93.61 indicates this is a high, fast gear, ideal for high-speed riding on flat terrain.
Frequently Asked Questions (FAQ)
Gear Inches factors in the wheel size, providing a standardized measure of rollout distance per pedal stroke. Two bikes with the same Gear Ratio but different wheel sizes (e.g., 20-inch folding bike vs. 29-inch mountain bike) will travel different distances, making Gear Inches the better metric for comparison.
A typical climbing or “easy” gear ratio is often less than 1.5, and often approaches 1.0 (e.g., a 34T chainring with a 34T cog results in a 1.0 ratio). This allows the rider to maintain a high cadence (pedaling speed) while moving slowly uphill, conserving energy.
A wide gear ratio range (the difference between the highest and lowest available gear inches) gives the cyclist the versatility to handle a variety of terrain—from steep climbs (low gears) to fast descents and flat sprints (high gears)—without excessive changes in cadence.
No. For accurate calculations, you should use the measured, effective rolling diameter of your wheel and inflated tire, or use a reliable online calculator to convert your tire size (e.g., 700c x 25mm) to the true diameter in inches.