General Knowledge:
- Between 8 and 10 speeds, the overall width of a cassette does not increase as the number of gears climbs. (There are some exceptions.)
- To preserve the overall width of a cassette the same with each gear increase, the thickness of the cogs decreases.
- The spacing between the cogs decreases with each gear increase too.
Shimano
Shimano’s 8/9/10 and 11-speed MTB cassettes and hubs are cross-compatible.
Therefore, it’s possible to combine a 10-speed Shimano cassette with a 9-speed hub.
How is this possible?
- Smaller Cog Pitch with Each Gear increase
The term cog pitch refers to the center-to-center distance between two adjacent cogs.
By reducing that number, one decreases the overall width of the cassette and makes it possible to fit more cogs within the same space.
The table below contains the cog pitches of 8,9,10 and 11-speed MTB cassettes.
| Number of Speeds | Cog Pitch | Total Width |
|---|---|---|
| 8 | 4.8 mm | 35.4mm |
| 9 | 4.35mm | 36.5mm |
| 10 | 3.95mm | 37.2mm |
| 11 | 3.9mm | 40.6mm |
Conclusions:
- A 10-speed MTB cassette is only 0.7mm wider than a 9-speed model. This isn’t a substantial difference.
2. Thinner Sprockets
With each gear increase, the sprockets of a cassette get thinner.
The table below contains the data for 8,9,10 and 11-speed MTB cassettes:
| Number of Speeds | Sprocket Thickness |
| 8 | 1.85mm |
| 9 | 1.78mm |
| 10 | 1.6mm |
| 11 | 1.6mm |
SRAM
The above principles apply to SRAM’s 10-speed cassettes too. It’s possible to install a 10-speed SRAM PowerGlide cassette on a 9-speed SRAM or Shimano hub.
Campagnolo
9 and 10-speed Campagnolo cassettes are cross-compatible. However, you cannot install a 10-speed Campagnolo cassette on a non-Campagnolo 9-speed hub. (The spline cutout is proprietary.)
Road Cassettes
Shimano’s 10-speed road cassettes are actually narrower than the 9-speed versions. Therefore, it’s necessary to use a 1mm spacer when installing a Shimano 10-speed road cassette on a 9-speed hub.
What Are The Advantages Of Installing a 10-speed Cassette On a 9-speed Hub?
- Money-savings
The main goal of keeping the overall cassette width the same is to ensure upgrade paths without the need to replace the hub.
In this case, the user can simply install a 10-speed cassette without buying a new hub and rebuilding the wheel.
- Smoother Transitions
A larger number of cogs allows manufacturers to make smaller jumps between the gears. As a result, the rider has an easier time maintaining a high cadence (rotations of the cranks per minute).
By pedaling at an optimal cadence, the rider can maintain a higher average speed for longer.
The Downsides of Installing a 10-speed Cassette on a 9-speed Hub
Spline Wear
10-speed specific freehub bodies often have taller splines. This is done intentionally to prolong the life of the freehub body.
The cogs of a 10-speed cassette are known to make cuts/dents into the freehub body because they’re thinner than 9-speed models and thus sharper.
Therefore, one could expect faster wear of the freehub body when combining a 10-speed cassette with a 9-speed hub.
That said, the wear accumulates slowly and it’s hard to say whether that’s a major negative.
What Parts Do I Need For Transitioning From 9-speed To 10?
If you’re upgrading from 9 to 10 speeds, the following parts will be required:
- a 10-speed shifter (unless you plan on using friction shifters that can support a 10-speed cassette)
- a rear derailleur with extra range or a derailleur hanger extender for your existing derailleur
- a 10-speed chain (10-speed cassettes need narrower chains due to the smaller cog pitch)
- a 10-speed cassette
If you want to run a single chainring, you will also need:
- a narrow-wide chainring
- а chain guide
Summary: What You Need To Know
- Shimano and SRAM’s MTB 10-speed cassettes can operate with 9-speed Shimano/SRAM hubs.
- Shimano’s 10-speed road cassettes can also be installed on a 9-speed hub by adding a 1mm spacer to the hub.
- Campagnolo’s 10-speed cassettes can be installed on a 9-speed hub but only when it’s made by Campagnolo too.
- The advantages of 10-speed cassettes are the smoother transitions between the gears allowing the rider to maintain optimal cadence.
