On a bicycle cassette, the difference between 11T, 12T, and 13T may look tiny—just one or two teeth. But with the same chainring and cadence, that difference directly changes the gear ratio and theoretical speed. Here, I compare 11T, 12T, and 13T using a 40T front chainring and an assumed 700×32C wheel circumference of 2.155m.
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. This article looks at the question from a beginner’s perspective while using formulas and numerical comparisons as carefully as possible. The speeds below are theoretical values based on gear ratio, cadence, and wheel circumference. Actual road speed will vary with rider power, wind, road surface, tires, pressure, riding position, and other conditions.
- Bottom line: 11T is about 18% faster than 13T at the same cadence
- How to calculate it
- Comparison at 60, 80, 90, and 100 rpm
- How big is the difference at 90 rpm?
- The cadence required for the same speed also changes
- 11T favors the high-speed end; 13T is slightly easier
- A sprocket change may require compatibility checks
- Summary
Bottom line: 11T is about 18% faster than 13T at the same cadence
With the 40T chainring fixed, the gear ratio is 3.64 with 11T, 3.33 with 12T, and 3.08 with 13T. At the same cadence, theoretical speed changes in the same proportion.
| Rear sprocket | Gear ratio (40T ÷ rear) | Relative to 11T |
|---|---|---|
| 11T | 3.64 | 100% |
| 12T | 3.33 | about 91.7% |
| 13T | 3.08 | about 84.6% |
So moving from 11T to 12T reduces theoretical speed by about 8.3% at the same cadence, while moving from 11T to 13T reduces it by about 15.4%. Going the other way, from 13T to 11T, raises theoretical speed by about 18.2%.
How to calculate it
The gear ratio is:
Gear ratio = front chainring teeth ÷ rear sprocket teethFor 40T × 11T:
40 ÷ 11 = 3.636...That means the rear wheel turns theoretically about 3.64 times for one crank revolution. Speed can then be calculated as:
Speed (km/h) = wheel circumference (m) × gear ratio × cadence (rpm) × 60 ÷ 1000Comparison at 60, 80, 90, and 100 rpm
Using a wheel circumference of 2.155m:
| Rear | 60 rpm | 80 rpm | 90 rpm | 100 rpm |
|---|---|---|---|---|
| 11T | 28.2 km/h | 37.6 km/h | 42.3 km/h | 47.0 km/h |
| 12T | 25.9 km/h | 34.5 km/h | 38.8 km/h | 43.1 km/h |
| 13T | 23.9 km/h | 31.8 km/h | 35.8 km/h | 39.8 km/h |
How big is the difference at 90 rpm?
At 90 rpm, 11T gives about 42.3 km/h, 12T about 38.8 km/h, and 13T about 35.8 km/h.
| Comparison | Speed difference |
|---|---|
| 11T − 12T | about 3.5 km/h |
| 12T − 13T | about 3.0 km/h |
| 11T − 13T | about 6.5 km/h |
Even a one- or two-tooth difference can become several km/h at higher cadence.
The cadence required for the same speed also changes
If the target speed is fixed, a smaller rear sprocket allows the same speed at a lower cadence. For example, to reach 40 km/h with this setup, you need roughly 85 rpm on 11T, 93 rpm on 12T, and 101 rpm on 13T.
Here, “faster” means a higher theoretical speed at the same cadence. Installing an 11T sprocket does not automatically make your actual road speed higher. You still need enough rider power to turn the taller gear.
11T favors the high-speed end; 13T is slightly easier
An 11T sprocket gives more high-speed headroom, but at the same road speed it also means a taller gear and more force required at the pedals. A 13T sprocket reduces top-end gearing but can be easier to use within an everyday cadence range.
For city riding, where stops and speed changes are frequent, spacing between usable gears can matter more than theoretical top speed.
A sprocket change may require compatibility checks
Whether 11T is usable depends on the cassette design, freehub body, rear derailleur capacity, chain length, and drivetrain compatibility. Tooth count alone does not guarantee that a particular sprocket or cassette will fit.
Summary
With a 40T chainring and 2.155m wheel circumference, theoretical speed at 90 rpm is about 42.3 km/h with 11T, 38.8 km/h with 12T, and 35.8 km/h with 13T. The gap between 11T and 13T is about 6.5 km/h.
A smaller rear sprocket does increase theoretical speed at the same cadence, but real-world speed depends on whether the rider can actually produce enough power to turn that gear.
