This post compares the advantages and disadvantages of 11-25 and 12-25 bicycle cassettes.
The Advantages Of 12-25 Cassettes
- An Extra Mid-Gear
The obvious difference between 11-25 and 12-25 cassettes are the smallest cogs (11vs.12). However, this isn’t the only dissimilarity.
A typical 10-speed 11-25 cassette has the following cogs: 11-12-13-14-15-17-19-21-23-25
Meanwhile, the gearing of a 12-25 cassette is 12-13-14-15-16-17-19-21-23-25.
Or in other words, the mid-range of the cassettes is 14-15-17-19 (11-25) vs. 14-15-16-17 (12-25).
This is a major advantage for 12-25 cassettes because the shifts are closer to each other and thus more fluid. And since the mid-range of the cassette is the most used one, many cyclists find this property a good enough reason to pick a 12-25 model.
In contrast, 11-25 cassettes come with a gap between the 15T and 17T cog. The end result is less fluid shifting. (Note: Sometimes the gap is the 18T cog.)
The Advantages of 11-25 Cassettes
- Higher Top Speed
The main advantage of an 11-25 cassette is the higher top speed that the unit offers when the same cranks are used.
One tooth difference may seem insignificant but it does have an effect.
This can be easily illustrated by comparing two hypothetical drivetrains:
Option A: 11-25 cassette + 42T chainring
Option B: 12-25 cassette + 42T chainring
In case A, the highest gear of the bicycle is 11:42 and results in a 1: 3.8 gear ratio.
The gear ratio reveals how many times the rear cog and consequently the rear wheel spins per 1 rotation of the chainring or cranks.
In this first scenario, the rear wheel will make 3.8 revolutions for every rotation of the cranks.
In case B, the gear ratio is 12: 42 = 1:3.5. Thus, the rear wheel will perform 3.5 revolutions per 1 revolution of the cranks.
If the rider is pedaling at the same RPM (rotations of the cranks per minute), the 11-42 gear will result in a greater top speed.
For example, if the rider is operating at 90 RPM, the cranks will make 90 rotations per 60 seconds. Those 90 rotations will result in 342 revolutions of the rear wheel.
In contrast, a 12/42 gear will result in 90×3.5=315 revolutions of the rear wheel. Therefore, the bike will cover a smaller distance in the same amount of time and will therefore move at a slower speed.
To calculate the speed of the bikes, one also has to know the circumference of the wheels.
For example, a 700x25c tire has a rough circumference of 2111mm.
In case A, the covered distance will be 2111mm x 342 revolutions = 721,962mm = 721.96 meters.
In case B, the covered distance will be 2111mm x 315 revolutions = 664,965mm = 664.96mm.
The speed of bike A will be 12.0327 m/s / 43.31km/h / 26.91mi/h.
The speed of bike B will be 11.0833 m/s / 39.9 km/h / 24.7927 mi/h.
Or in other words, the 11-25 cassette offers an 8.54% higher top speed.
Note: This number isn’t universal and applies only in the current situation because the chainring size, the RPM of the rider, and the circumference of the wheels directly affect the bicycle speed too. Thus, one cannot conclude that an 11-25 cassette is 8.54% faster than a 12-25 one in all cases.
- Extra Speed While Running a Smaller Chainring
The 11T cog allows the user to maintain high top speed while relying on a smaller chainring. Hence why 11-25 cassettes are often coupled with compact cranks.
Unlike standard cranks (53T, 39T), compact cranks usually come with a 50T and a 34T chainring.
The top speed of a bicycle equipped with a compact 50/34 crankset and an 11-25 cassette is 32.86mph/52.88km/h at 90 RPM.
Meanwhile, the top speed of a bike with a standard crankset and a 12-25 cassette is 31.93mph/51.38km/h at 90 RPM.
The true benefit of combining an 11-25 cassette with a compact crankset is the lower gear that the bike acquires.
A 25/34 gear has a 1:1.36 ratio. Meanwhile, a standard crankset offers a 25/39 gear resulting in a 1:1.56 ratio. (Note: The numbers 34 and 39 refer to the teeth on the smaller chainring.)
In short, a compact crank + an 11-25 cassette offers practically the same top speed as a 12-25 cassette + standard crank but also a lower gear which is highly beneficial when climbing.
Note: Combining an 11-25 cassette with a compact crankset has a negative side too, namely the reduction of speed when pedaling in the mid-gears. Thus, one can argue that a 11-25 cassette + a compact crankset combo hurts the rider’s average speed.
For example, riding in 50/15 at 90 RPM results in 24.10mph/38.7kph top speed whereas 53/15 offers a top speed of 25.54mph/41kph. In the world of competitive cycling, a 1.42mph/2.3kph difference is big.
The Disadvantages Of 11-25 Cassettes
- Lack of Fluidity
The missing 16T or 18T cog hurts the fluidity of the shifting experience in the most used gears. While this isn’t the end of the world, some cyclists might find it annoying.
- А Rarely Used High Gear
Тhe 11T cog offers a higher top speed, but the increase isn’t substantial. Moreover, a 12T cog provides more than enough speed for most people.
- Faster Wear of The Cog
Cogs with fewer teeth are expected to have a shorter lifespan because the stress of the chain is spread over a smaller surface.
- Non-compatible with Standard Hubs by Default
11-25 cassettes require a special hub which in the case of Shimano is known as HyperGlide-C. The letter “C” stands for compact.
The splines of HyperGlide-C cassettes are ever so slightly shorter than those of regular hubs. Consequently, the 11T cog slides on the hub only partially. The purpose of this engineering is to ensure the optimal distance between the cogs.
For security and clearance reasons, cassettes with an 11T sprocket come with a special lock ring that’s smaller than the classic version. If a standard lock ring is used, the chain will rub against it and won’t run properly when positioned on the 11T cog.
An 11-25 cassette cannot be installed on a non-HyperGlide-C cassette by default. However, the combination can work by placing a 1mm spacer on the driver hub body before sliding the cassette.
Who Are 11-25 Cassettes For?
An 11-25 cassette might appeal to the following cyclists:
- Road cyclists who want to run a very high gear to maintain incredible top speed.
- Road cyclists who want to use a compact crankset without losing overall gear range.
- Commuters looking to increase their top speed without switching to a larger chainring.
Who Are 12-25 Cassettes For?
Truth be told, 12-25 cassettes are a better choice for most people for the following reasons:
- No need for special hubs
- Fluid shifting in the most used gears
- The 12T cog offers a lower gear, but it’s more than fast enough for most cyclists. If the cyclist isn’t using the 12T cog frequently, then an 11T cog will be used even less.