Condensed answer: A 7-speed cassette can be installed on an 11-speed hub. Since 7-speed cassettes are narrower than 11-speed cassettes, the installation will require the use of a spacer to make up for the gap left on the hub.
Cassette Width and Hub Spacing
11-speed hubs are designed for 11-speed cassettes which are wider than 7-speed cassettes.
Therefore, a 7-speed cassette leaves a gap when installed on an 11-speed hub.
For that reason, it’s necessary to install a spacer before mounting the actual cassette. The spacer acts as a dummy occupying space. Without it, the cassette will move from left to right and create drivetrain instability.
Compensating for the Gap With Spacers
To determine the size of the spacer needed to install a 7-speed cassette on an 11-speed hub, one first needs to know the width of the freehub body.
The freehub body is the part of the hub on which the cassette slides. This is also the element of the hub that contains the pawls making a clicking noise by brushing against a ratchet ring (read more).
The table below contains the freehub body width of 11-speed MTB and road rear hubs:
|Number of Speeds||Road Freehub Body||MTB Freehub Body|
Now that we know the freehub body width, we have to deduct the width of a 7-speed cassette from it to find the width of the needed spacers.
The width of a 7-speed cassette is 31.5mm to 32.8mm depending on the brand and model.
This leads us to the following conclusions:
- A spacer between 3.95mm and 5.25mm is needed when installing a 7-speed cassette on an 11-speed road hub.
- A spacer between 2.15mm to 3.45mm is needed when installing a 7-speed cassette on an 11-speed MTB hub.
FAQ: Why are 11-speed road hubs wider?
11-speed road hubs are made wider to push the largest cog (lowest gear) away from the spokes and prevent rubbing.
Road bikes have smaller low gears (e.g., a 28t sprocket). Since the sprocket is of smaller diameter its periphery is closer to the base of the spokes. As a result, there’s a chance for the chain to come in contact with the spokes and rub against them.
Spokes are fairly thin, and the chain will quickly eat through them and cause wheel failure.
MTB cassettes do not have this problem because they have a larger low gear, and the cog successfully clears the spokes.
A Note on O.L.D. and Spacing
It’s also important to note that 7-speed and 11-speed bicycles have different Over-the-locknut Dimension (O.L.D.).
The term O.L.D. refers to the usable part of the hub from one locknut to the other. Naturally, the dropouts need to have the same spacing for the hub to fit.
Road frames originally designed for 7 speeds have a 126mm rear dropout spacing. Meanwhile, 11-speed road hubs require 130mm spacing (caliper brakes) or 135mm spacing (disc brakes). 11-speed MTB hubs also use 135mm spacing unless the system is boosted in which case the dropouts have to be even further apart.
Therefore, if you’re trying to combine an 11-speed hub with a 7-speed cassette on a 7-speed frame, you will face a compatibility issue – the hub won’t fit into the frame.
If the frame is made of steel, you can cold-set it (a fancy word for bending) to the required O.L.D.
Steel frames can be cold set because the material has higher ultimate tensile strength than yield strength.
The ultimate tensile strength of a material describes the amount of stress that it can withstand before losing integrity and eventually breaking.
The yield strength, on the other hand, is the point beyond which the material permanently deforms.
Conversely, aluminum and carbon frames should never be cold set because the materials have a yield strength really close to their ultimate strength and lose their integrity easily.
If the frame is not suitable for cold-setting, you will have to use a 7-speed hub or replace the entire frame.
Summary: What You Need to Know
- A 7-speed cassette can be installed on an 11-speed hub.
- 11-speed hubs have a wider freehub body than the one found on 7-speed hubs.
- To make up for the gap that opens, one needs to install a spacer before fitting the cassette.
- If the 11-speed hub is designed for MTBs, the spacer has to be between 2.15mm to 3.45mm depending on the cassette’s width.
- If the 11-speed hub is built for road bikes, the spacers have to be between 3.95mm and 5.25mm.
- If the frame is designed for 7-speeds, it will be too narrow for an 11-speed hub. If it’s made of steel it can be spread to the needed width. If not, a new frame or hub will be needed for this conversion.