General Knowledge
As the number of speeds grows, the width of bike cassettes doesn’t increase dramatically.
The goal is to make rear hubs compatible with the widest number of cassettes out there so that the user doesn’t have to replace the rear hub and re-lace the wheel.
The above is achieved by making the sprockets thinner and decreasing the cog pitch. The cog pitch is the center-to-center distance between each cog. Thanks to this engineering, the width discrepancy between cassettes is kept minimal.
Shimano
MTB
Shimano’s 8, 9, 10, 11 and 12-speed MTB cassettes are of roughly the same width.
Consequently, Shimano’s 9-speed hubs can directly accept a 12-speed MTB cassette.
The table below contains the width of 8-12-speed cassettes:
| NUMBER OF SPEEDS | TOTAL WIDTH |
|---|---|
| 8 | 35.4mm |
| 9 | 36.5mm |
| 10 | 37.2mm |
| 11 | 40.6mm |
| 12 | 41.2mm |
According to the data above, 12-speed cassettes are 4.7mm wider than 9-speed models. As a result, the smallest cog of the 12-speed cassette will sit a little taller. That said, the lock ring can still “compress” and secure the cassette effectively.
Microspline
The above applies only to Shimano cassettes labeled as HyperGlide.
If the cassette is part of Microspline family, it can’t be installed on a 9-speed hub and works only on Microspline models. (The splines of Microspline hubs are completely different from those found on 9-speed HyperGlide cassettes.)
Road
There’s some overlap between 11 and 12-speed road and MTB cassettes. Hence why it’s totally possible to see an MTB running a road cassette.
That said, 12-speed road cassettes labeled as HyperGlide compatible should work on 9-speed hubs too.
If the cassette, however, is from the Microspline family, it won’t work with a 9-speed hub as they come only in a HyperGlide version.
SRAM
SRAM’s 12-speed NX cassettes can be installed on standard 9-speed SRAM and Shimano hubs (the type of hubs compatible with the PowerGlide and HyperGlide cassettes).
However, SRAM’s GX cassette requires an XD driver. Or in other words, it’s not possible to install a GX cassette on a standard Shimano or SRAM 9-speed hub. This conversion will require a hub with an XD driver.
Campagnolo
A 12-speed Campagnolo cassette can be installed on a 9-speed hub but only when the hub is also made by Campagnolo.
Campagnolo cassettes are not compatible with Shimano and SRAM hubs.
What is the advantage of a 12-speed cassette over a 9-speed model?
- Smoother transitions
The extra cogs on the cassette make the jumps between gears smaller. As a result, the rider can maintain a smooth cadence. Cadence is a term describing the rotation of the cranks per minute. High cadence (e.g., 90 RPM) is associated with higher average speeds and lower energy expenditure.
What are the downsides of installing a 12-speed cassette on a 9-speed hub?
The main downside of this conversion are the extra expenses. A switch from 9 to 12 speeds will require the following parts:
- New hub (If the current isn’t compatible. The wheel will have to be rebuilt too.)
- New cassette (12-speed cassettes aren’t the cheapest.)
- 12-speed shifter + cable + housing
- New derailleur if the current one cannot cover the entire cassette.
