Bicycle speed depends not only on cadence, but also on gear ratio and tire circumference. This article calculates the theoretical speed at 60, 80, 90, and 100 rpm and compares the results numerically.
About this article: I am not a professional cyclist, bicycle mechanic, or competitive rider. I am a beginner learning about bicycles through riding, research, and calculation. I use publicly available information, basic physics, and formulas to examine questions from a beginner’s point of view. Actual speed varies with rider power, wind, road surface, tires, pressure, riding position, and other conditions, so the figures below should be treated as theoretical values or estimates.
What is cadence?
Cadence is the number of crank revolutions per minute, expressed in rpm. At 60 rpm the crank turns once per second; at 90 rpm it turns 1.5 times per second.
Speed formula
Gear ratio = front chainring teeth ÷ rear sprocket teeth
Speed (km/h) = tire circumference (m) × gear ratio × cadence (rpm) × 60 ÷ 1000For this example, tire circumference is assumed to be 2.155 m, roughly representative of a 700×32C setup, with a 40T front chainring. Rear sprockets of 11T, 15T, and 28T are compared.
Theoretical speed at 60, 80, 90, and 100 rpm
| Gearing | Gear ratio | 60 rpm | 80 rpm | 90 rpm | 100 rpm |
|---|---|---|---|---|---|
| 40T × 11T | 3.64 | 28.2 km/h | 37.6 km/h | 42.3 km/h | 47.0 km/h |
| 40T × 15T | 2.67 | 20.7 km/h | 27.6 km/h | 31.0 km/h | 34.5 km/h |
| 40T × 28T | 1.43 | 11.1 km/h | 14.8 km/h | 16.6 km/h | 18.5 km/h |
Why the same cadence can produce different speeds
At the same 90 rpm, 40T × 11T gives about 42.3 km/h while 40T × 28T gives about 16.6 km/h. The difference comes from gear ratio: each crank revolution turns the rear wheel a different number of times. Cadence alone therefore cannot determine road speed.
If gearing stays the same, speed rises in direct proportion to cadence
With the same gear ratio and tire circumference, theoretical speed is directly proportional to cadence. Increasing cadence from 60 to 90 rpm is a 1.5× increase, so theoretical speed also becomes 1.5× higher. With 40T × 15T, that means about 20.7 km/h at 60 rpm and 31.0 km/h at 90 rpm.
Does 100 rpm automatically mean faster riding?
Only in a theoretical drivetrain calculation. In real riding, the rider must be able to sustain that cadence and the required power. As speed rises, aerodynamic drag becomes much more important, so the power needed to keep accelerating also rises quickly. A high cadence does not automatically guarantee a high cruising speed.
Key point: It is more accurate to say “with the same gearing, higher cadence produces a higher theoretical speed” than simply “higher cadence means faster riding.”
How to use cadence in real riding
On level roads, riders generally choose a gear that lets them maintain a comfortable cadence. If the pedals feel too light and spin out, shifting to a harder gear increases distance traveled per crank revolution. If the gear is too hard and cadence falls, shifting to an easier gear reduces the torque required at the crank.
Summary
Bicycle speed is determined by cadence, gear ratio, and tire circumference together. With a 2.155 m tire circumference and 40T × 11T gearing, theoretical speed is about 28.2 km/h at 60 rpm, 42.3 km/h at 90 rpm, and 47.0 km/h at 100 rpm. Whether those speeds can actually be sustained depends on rider power, aerodynamic drag, road conditions, and other real-world factors. Cadence is an important part of the calculation, but it does not determine speed by itself.
