Bicycle Gear Ratio & Speed Calculator
Compute gear ratio, roll-out (development) and predicted speed for a bicycle drivetrain from chainring, cog, cadence and wheel circumference.
How to Use the Bicycle Gear Ratio & Speed Calculator
- Enter chainring and cog tooth counts.
- Enter target cadence in rpm.
- Enter wheel circumference in mm.
- Click Calculate.
使用场景
- •Choosing chainring/cassette combinations.
- •Comparing single-speed gear inches.
- •Teaching mechanical advantage in PE classes.
公式
Gear ratio = chainring / cog. Roll-out (m) = wheel circumference × ratio. Speed (km/h) = cadence × circumference × 60 × ratio / 1000.
常见问题
How do I measure wheel circumference?
Mark the valve, roll the loaded bike one full turn on flat ground, measure the distance. Typical road 700×25c ≈ 2105 mm; MTB 29×2.2 ≈ 2300 mm.
What cadence is optimal?
80–95 rpm is the classic self-selected range for trained cyclists. Track sprinters can peak above 130 rpm.
Does this account for chain drag?
No. Real-world speed is 2–4% lower because of chain, tyre and air losses at low speed and dramatically more at high speed.