Cassette width: It’s logical to expect a cassette with fewer gears (e.g., 10-speed) to be narrower than a cassette with more gears (e.g., 11-speed), but this isn’t the case.
The overall width of cassettes changes very little with each gear increase or decrease. The purpose of this engineering is to ensure that one hub can accept different cassettes.
The width of the cassette is preserved within tight tolerance by making the cogs thinner with each gear increase. As a result, it’s possible to fit more and more within roughly the same dimensions.
The Differences Between 11-speed MTB and Road Hubs
11-speed MTB and road hubs use freehub bodies of different widths. The freehub body is the part of the rear hub on which the cassette slides. It’s also the element containing the pawls that brush against an engagement ring to create the buzz sound that freehubs make.
11-speed MTB freehub bodies are 1.85mm narrower than 11-speed road freehub bodies.
11-speed road hubs are wider so that the last sprocket can be further away from the spokes.
Road cassettes have a higher gearing (e.g., 11-25) than MTBs. As a result, the largest sprocket ends up in great proximity to the spokes. When the chain is on that sprocket, it can literally rub against the spokes and “eat” them.
To avoid this issue, 11-speed road cassettes are slightly wider. 11-speed road hubs have no choice but to reflect the extra width.
Meanwhile, MTB cassettes come with larger lower gear (e.g., 42t large cog). The teeth of the larger cog are higher and thus further away from the spokes. Consequently, there’s no need for a wider cassette and hub.
Enter The World Of Cassette Spacers
It’s possible to ensure compatibility between 10-speed cassettes and 11-speed hubs via spacers.
Option 1: A 10-speed MTB Cassette On an 11-speed Road Hub
Shimano’s 11-speed road cassettes are approximately 1.85mm wider than 11-speed MTB cassettes. The 11-speed road hubs reflect that.
Therefore, you will have to install a 1.85mm spacer on an 11-speed road hub if you want to use the hub with a 10-speed MTB cassette. Precisely for that reason, many 11-speed road hubs come with a 1.85mm spacer by default.
Option 2: A 10-speed MTB Cassette On an 11-speed MTB Hub
A 10-speed MTB cassette can be directly installed on an 11-speed MTB hub without the need for spacers.
Option 3: A 10-speed Road Cassette On an 11-speed Road Hub
Shimano’s 10-speed road cassettes are actually narrower than 8, 9 and 11-speed models. For that reason, it’s necessary to use 2 spacers (1mm + 1.85mm) when combined with 11-speed road cassettes.
The 1mm makes the 10-speed road cassette as wide as an 8 or 9-speed model.
The 1.85mm spacer is there to make the 11-speed hub compatible with 8-9-speed cassettes.
Option 3: A 10-speed Road Cassette On an 11-speed MTB Hub
As already mentioned, 11-speed MTB hubs aren’t extra wide. Therefore, the 1.85mm spacer isn’t needed.
However, it’s necessary to install a 1mm spacer because 10-speed road cassettes are slightly narrower. The 1mm spacer makes the 10-speed road cassette as wide as the 9 and 8-speed models.
Note: The above information applies only to Shimano and SRAM’s components.
Campagnolo’s 11-speed hubs can accept 10-speed Campagnolo cassettes right away without the need for spacers. However, you can only use Campagnolo cassettes with a Campagnolo hub. Otherwise, the cassette won’t even slide onto the hub.
The Pros of Combining a 10-speed Cassette and an 11-speed Hub
Parts Recycling (money savings)
If you have an 11-speed hub but want to integrate it into a 10-speed drivetrain, the combination will save you money and eliminate the need to buy a new hub.
A 10-speed MTB hub can work with an 11-speed MTB cassette but is incompatible with an 11-speed road cassette.
If you have a road bike and plan to upgrade to 11 speeds, and you can find an 11-speed hub for cheap, you can use it with your current 10-speed drivetrain and eventually build an 11-speed transmission.
10-speed parts (derailleurs, cassettes, chain…etc.) are cheaper than the 11-speed equivalents.
The Cons of Running a 10-speed Cassette on an 11-speed Hub
One of the downsides is the need to source spacers (1.85mm, 1mm) if you have a road hub.
Bigger Gear Jumps
10-speed cassettes come with larger jumps between the gears. Consequently, the rider has a harder time maintaining a high cadence at all times.
Cadence is the number of crank rotations per minute. It’s accepted that a high cadence (e.g., 90RPM) increases one’s average speed while minimizing fatigue and lowering joint stress.
Having said that, 10 gears are still plenty smooth, especially for recreational riders.
Summary: What You Need To Know
Shimano and SRAM’s 10-speed MTB cassettes can be installed on Shimano and SRAM 11-speed MTB hubs without modifications.
Shimano and SRAM 10-speed MTB cassettes need a 1.85mm spacer when installed on Shimano and SRAM 11-speed Road Hubs
Shimano and SRAM 10-speed Road cassettes need two spacers (1mm + 1.85mm) when installed on Shimano and SRAM 11-speed road hubs.
Campagnolo 10-speed cassettes can be installed on 11-speed Campagnolo hubs right away.
11-speed Campagnolo hubs can accept only Campagnolo cassettes.