Gear & Speed Calculator
Speed is how far one pedal turn moves the bike — wheel circumference × chainring ÷ cog — times your cadence. On 27.5 × 2.4 tires with a 44-tooth chainring and an 11-tooth cog, one pedal turn moves the bike 8.87 m, so 80 rpm is about 26.5 mph and 20 mph — where Class 1 and 2 assist stops — takes only 60 rpm.
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Your drivetrain
Speed in each gear
Top gear at 80 rpm
26.5mph
44/11
Easiest gear
6.9mph
44/42, 29 gear-in
20 mph in top gear
60rpm
where Class 1 and 2 assist stops
Past the 20 mph assist cutoff from 44/13 up
How this was calculated
| Gear | Gear inches | Development | Gain ratio | mph at 80 rpm | rpm for 20 mph | rpm for 28 mph |
|---|---|---|---|---|---|---|
| 44/42 | 29.1 | 2.32 m | 2.18 | 6.9 | 231 | 323 |
| 44/37 | 33.1 | 2.64 m | 2.47 | 7.9 | 203 | 285 |
| 44/32 | 38.2 | 3.05 m | 2.86 | 9.1 | 176 | 246 |
| 44/28 | 43.7 | 3.49 m | 3.26 | 10.4 | 154 | 215 |
| 44/24 | 51.0 | 4.07 m | 3.81 | 12.1 | 132 | 185 |
| 44/21 | 58.2 | 4.65 m | 4.35 | 13.9 | 115 | 162 |
| 44/18 | 67.9 | 5.42 m | 5.08 | 16.2 | 99 | 139 |
| 44/15 | 81.5 | 6.51 m | 6.09 | 19.4 | 82 | 115 |
| 44/13 | 94.1 | 7.51 m | 7.03 | 22.4 | 71 | 100 |
| 44/11 | 111.2 | 8.87 m | 8.31 | 26.5 | 60 | 85 |
Worked example
44/11 on 27.5 × 2.4 tires, 170 mm cranks, 80 rpm
Wheel: 584 mm bead seat + 2 × 61 mm tire ≈ 706 mm tall. Development: 0.706 × π × 44 ÷ 11 = 8.87 m per pedal turn. Speed: 8.87 × 80 × 60 ÷ 1,000 = 42.6 km/h = 26.5 mph. Gear inches: 27.8 × 44 ÷ 11 = 111. Past 20 mph a Class 1 or 2 motor stops helping, so on this bike the top few gears are pedal-only territory.
Reference
Speed at 80 rpm by gear and wheel size (mph)
Top gears common on e-bikes. The cadence you’d need to reach 20 mph is in brackets.
| Gear | 700 × 45 | 27.5 × 2.4 | 26 × 4.0 | 20 × 4.0 |
|---|---|---|---|---|
| 44/11 | 26.7 (60 rpm) | 26.5 (60 rpm) | 28.6 (56 rpm) | 22.9 (70 rpm) |
| 48/11 | 29.1 (55 rpm) | 28.9 (55 rpm) | 31.2 (51 rpm) | 24.9 (64 rpm) |
| 52/11 | 31.5 (51 rpm) | 31.3 (51 rpm) | 33.8 (47 rpm) | 27.0 (59 rpm) |
| 44/14 | 21.0 (76 rpm) | 20.8 (77 rpm) | 22.5 (71 rpm) | 18.0 (89 rpm) |
How to use it
In 4 steps
- 1Type the tire size from the sidewall — the tool works out the wheel's real diameter.
- 2Count the chainring teeth (stamped on it) and pick your cassette, or type each cog's teeth.
- 3Enter your cadence: count pedal turns for 15 seconds and multiply by 4.
- 4Read the speed in every gear and the cadence where the assist cutoff arrives.
Gearing on an e-bike
A motor changes what gearing is for. On a regular bike the top gear decides your flat-out speed; on a Class 1 or 2 e-bike the motor stops helping at 20 mph, so a very tall top gear mostly matters if you’ll pedal past that on your own. The easy end matters more: a low gear keeps cadence up on climbs, which is where mid-drive motors work best.
Sheldon Brown’s three measures all say the same thing in different units. Gear inches is the old high-wheeler comparison; development is the distance per pedal turn in meters; gain ratio adds crank length, so it’s the only one that compares bikes with different cranks fairly. Wheel size matters too — a 20 × 4 fat tire stands much shorter than a 700c, so the same gears are slower.
FAQ
Gear & speed: questions
How do I calculate bike speed from gear and cadence?
Multiply the distance one pedal turn moves the bike (wheel diameter × π × chainring teeth ÷ cog teeth) by your cadence. A 706 mm wheel with a 44/11 gear moves 8.87 m per pedal turn; at 80 rpm that's 42.6 km/h, or about 26.5 mph.
What are gear inches?
Sheldon Brown's definition: the drive wheel's diameter in inches, times the chainring teeth, divided by the cog teeth. A 27-inch wheel with a 53/19 gear is about 75 gear inches — the size of high-wheeler you'd need to go as far per pedal turn.
At what cadence does e-bike assist stop?
It stops at a speed, not a cadence: 20 mph for Class 1 and 2, 28 mph for Class 3 (California Vehicle Code §312.5). The cadence depends on gear and wheel — about 60 rpm on a 44/11 with 27.5 × 2.4 tires, far more in lower gears.
Why is my fat-tire e-bike slower in the same gear?
A 20 × 4 wheel stands about 610 mm tall against roughly 712 mm for a 700 × 45, so each pedal turn covers less ground. In the same 44/11 gear at 80 rpm, that's about 22.9 mph instead of 26.7.
Something not answered here? Just ask — I’d rather talk it through than have you guess.
Sources
Where these numbers come from
- [1]Sheldon Brown, “Gain Ratios” (opens in a new tab)Definitions of gear inches, development and gain ratio, with worked examples.
- [2]California Vehicle Code §312.5 (opens in a new tab)Assistance stops at 20 mph (Class 1 and 2) and 28 mph (Class 3).
- [3]Sheldon Brown & John Allen, “Tire Sizing Systems” (opens in a new tab)Bead seat diameters used for wheel size.
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Related tools
- Chain Wear CheckerMeasure with a ruler or a checker tool; see how worn it is and what waiting will cost.
- California E-Bike Class CheckerClass 1, 2, 3 — or legally a motorcycle. The rules that come with each, with the statute cited.
- Tire Size DecoderAny tire marking to its real size — and which tube actually fits.
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