Bike Speed Calculator

Your bicycle's forward speed is determined by combining rotational mechanics with tire circumference. First, the calculator computes your gear ratio by dividing the number of teeth on your front chainring by the teeth on your rear cog: gearratio = chainring / cog. Next, it calculates the total wheel circumference using your rim diameter and tire width: Circumference = pi * (diameter + (2 * tire_size)). Finally, multiplying the gear ratio, wheel circumference, and your pedaling cadence (RPM) yields your total linear speed, factoring in time conversion units for miles per hour or kilometers per hour.

Imagine you are riding a road bike with a 50-tooth chainring and an 11-tooth rear cog, giving you a gear ratio of 50 / 11 = 4.545. Assume your wheel diameter is 27 inches with a 1-inch tire size, leading to a total wheel diameter of 29 inches. Multiplying this by pi gives a circumference of approximately 91.1 inches. If your cadence is a steady 90 RPM, you multiply 91.1 inches by 4.545 (gear ratio) by 90 (cadence) to find your distance traveled per minute. Converting this into standard road metrics reveals a cruising speed of roughly 24.5 miles per hour.

When analyzing your bike speed, remember that real-world conditions like headwinds, rolling resistance, and slope gradients will alter your actual velocity compared to pure mathematical outputs. Additionally, maintaining a higher cadence with a slightly easier gear is often more efficient for endurance riding than grinding a massive gear at a low RPM. Always measure your actual tire circumference by sitting on the bike rather than relying solely on the printed sidewall number for maximum accuracy.