Cassette width. It’s logical to conclude that cassettes with more gears are wider than models with fewer gears. However, this isn’t exactly the case. The overall width of the cassette doesn’t increase much when going from 8 to 12 speeds.
By making the cogs thinner with each gear increase, it’s possible to fit more and more within roughly the same dimensions.
Hence why the inner width of bike chains drops as the number of speeds increases. More speeds equal thinner cogs and consequently require a narrower chain.
The spacing between the cogs decreases with each gear increase too.
As a result, it is, for example, possible to install 10-speed cassettes on 8-speed hubs.
Shimano’s MTB hubs can directly accept 12-speed MTB cassettes because Shimano’s 8, 9, 10, 11 and 12-speed MTB cassettes are of roughly the same width.
The standard 11-speed MTB Shimano hubs reflect that.
However, Shimano’s 11-speed road hubs are 1.85mm longer than the 11-speed MTB hubs.
11-speed road hubs are wider so that the last sprocket can be further away from the spokes.
Road bikes have a higher low gear than MTBs (e.g., 28T big cog). Subsequently, the edges of the largest cog sit low and dangerously close to the spokes. When you add the chain, you have a recipe for chain rubbing that could quickly result in an “eaten wheel”.
To prevent this outcome, 11-speed cassettes are made wider. The hubs have no choice but to reflect this.
That said, an 11-speed road hub is still compatible with a 12-speed MTB cassette with the use of a 1.85mm spacer (some 11-speed hubs come with a spacer by default) and a 12-speed road cassette without a spacer.
Shimano Microspline Hubs
The newest 11 and 12-speed Shimano hubs are shorter and have a 23-spline freehub body.
As a result, they are not compatible with standard HG (HyperGlide) cassettes.
Shimano Mircospline hubs are compatible only with 11 and 12-speed XTR cassettes.
SRAM’s 12-speed NX cassettes can be installed on standard 11-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 11-speed hub. This conversion will require a hub with an XD driver.
Standard Campagnolo 12-speed cassettes can readily fit on 11-speed Campagnolo hubs.
However, Campagnolo cassettes have a proprietary cutout and are not compatible with non-Campagnolo hubs regardless of speeds.
FAQ: What is the benefit of replacing an 11-speed cassette with a 12-speed one?
The main advantage of 12-speed cassettes would be the smaller gaps between the gears. The smaller the gap, the less the rider feels the transition between each cog. Consequently, it’s easier to maintain a steady cadence (rotation of the cranks per minute).
Optimal cadence results in greater average speed while strategically spreading the rider’s effort over the largest possible distance.
That said, the difference between 11 and 12-speed cassettes isn’t fundamental and cannot make or break a cyclist unless one is competing at the highest level.
Summary: What You Need To Know
- Shimano’s 12-speed MTB HyperGlide cassettes can be installed on 11-speed Shimano MTB hubs designed for Hyperglide cassettes.
- Shimano’s 12-speed MTB cassettes can also be installed on 11-speed Shimano road cassettes with the use of a 1.85mm spacer.
- Shimano’s 12-speed MTB cassettes can work with SRAM’s 11-speed hubs designed for SRAM’s PowerGlide cassettes.
- SRAM’s 12-speed NX cassettes can work on 11-speed Hyperglide Shimano hubs as well as 11-speed SRAM Powerglide hubs.
- SRAM’s 12-speed GX hubs are compatible only with hubs that have an XD driver.
- Campagnolo 12-speed cassettes are compatible with 11-speed hubs, but only when the hub is made by Campagnolo as well.