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Condensed answer: An 8-speed MTB hub is wide enough to accept an 11-speed MTB cassette.

An 8-speed Road hub, however, is too narrow for an 11-speed Road cassette.

If you have an 8-speed road bike and want to convert it to 11 speeds, you will have to replace the hub with an 11-speed one.

Requirements for Fitting an 11-speed Cassette On an 8-speed Hub

Proper Hub Spacing

The number one requirement for an 11-speed cassette to be compatible with an 8-speed hub is spacing.

If a cassette is too wide for a hub, then it won’t fit at all. If it’s too narrow, it won’t be secure by itself and will require the use of spacers.

11-speed MTB cassettes are about as wide as 8/9/10-speed MTB cassettes. Subsequently, an 8-speed MTB hub can accept 8/9/10 and 11-speed cassettes.

At first, this information may seem a bit confusing because it’s logical to assume that an 11-speed cassette is wider than an 8-speed one due to the presence of 3 more cogs/gears.

However, the width of a cassette does not change all that much with speed increases.

Only the center to center distance between the cogs (cog pitch) decreases. The thickness of the cogs remains the same.

Hence why 11-speed cassettes require narrower chains to ensure smooth shifting and no rubbing between the chain and the adjacent cogs.

11-speed road cassettes are a bit different. They are 1.85mm wider than 8/10/11-speed MTB cassettes. This is done to push the largest cog away from the spokes.

Why?

Road cassettes have a smaller low gear (e.g., 25-28th cog). When riding in it, there’s a chance that the chain will rub against the spokes. To prevent this outcome, the cassette is pushed further away from the spokes.

MTB cassettes do not have this problem because they have a larger low gear, and the cog successfully clears the spokes.

Parts Needed for Аn 8-speed to 11-speed Conversion

Below you will find the most common 8-to-11-speed conversions and the new components that each version necessitates:

MTB 8-to-11 Speed Conversion

Required parts:

1. 11-speed MTB cassette

2. 11-speed chain

3. 11-speed rear derailleur

4. 11-speed trigger shifter

5. New gear cable + housing (optional)

Road 8-to-11 Speed Conversion (all road parts)

1. 11-speed road cassette

2. 11-speed road hub (you will also have to re-lace the rear wheel around an 11-speed hub or buy a new wheel with an 11-speed hub on it)

3. 11-speed chain

4. 11-speed rear derailleur

5. 11-speed brake-shifters (or some sort of friction shifters that support 11 speeds)

6. New gear cable + housing (optional)

Road 8-to-11 Speed Conversion (MTB + Road Parts)

It’s also possible to use an 11-speed MTB cassette for a road conversion. By doing so, you won’t have to buy a new hub. However, the cassette will have to be paired with an MTB derailleur and shifter.

11-speed MTB and road derailleurs have different rear shift ratios. The rear shift ratio of the derailleur shows how much the derailleur moves per one 1mm of gear cable pulled or released by a shifter.

11-speed MTB derailleurs have a rear shift ratio of 1.1 whereas that of 11-speed road derailleurs is 1.4.

The different rear shift ratios prevent the use of an 11-speed road derailleur when relying on an 11-speed MTB cassette.

However, the derailleur isn’t the only source of incompatibility. 11-speed road shifters and 11-speed MTB shifters aren’t interchangeable either because they move a different amount of cable.

Consequently, this particular conversion requires MTB shifters. Thus, the option is viable only when the road bike has flat bars or the user is willing to use some sort of hack to mount MTB shifters onto the flat part of a drop bar.

Friction shifters are another alternative.

If you want to build a road wheel around an MTB hub, The O.L.D. of the hub has to match the spacing of the frame.

O.L.D. stands for over-locknut-dimension and refers to the usable part of a hub between the two locknuts.

If the O.L.D. of the hub is too wide for a frame, the wheel won’t fit regardless of what cassette it uses.

Below is a table containing the O.L.D. of road and MTB bikes:

Conclusion: A rear MTB hub can fit on a road bike only if the hub is not boosted, and the road bike is designed for disc brakes.

If you want to convert to 11-speeds via an MTB hub, the conversion is viable only when the frame has a 135mm dropout spacing.

With all those clarifications made, here’s the list of the components needed for a mixed (road + MTB) conversion from 8 to 11 speeds.

1. 11-speed MTB cassette

2. 11-speed chain

3. 11-speed MTB derailleur

4. 11-speed MTB shifter or a friction shifter

5. New cable + housing

The clear downside of this conversion is that one cannot use brake-shifters.

The upside is that you get extra range (MTB cassettes have lower gearing).

Why Do 11-Speed Road Hubs Come with Spacers?

Some 11-speed road hubs come with a 1.85mm and a 1mm spacer.

By adding a 1.85mm spacer to the hub, the usable part of the driver becomes narrower and thus compatible with 8/9/10/11-speed MTB hubs.

If you add both the 1.85mm and 1mm spacer, the 11-speed road hub will become compatible with 10-speed road cassettes too.

What Are The Benefits of an 8-to-11-Speed Conversion?

11-speed drivetrains have the following benefits over 8 speeds:

1. Lower Gears

An 11-speed cassette can offer substantially lower gearing than 8-speeds. For example, some MTB cassettes come with a 50th large cog.

Technically, there are some high-capacity 8-speed cassettes too, but they are rare and have major jumps between the gears – a negative when the goal of the cyclist is to maintain high cadence and smooth pedaling.

2. Smaller Jumps

The smaller the jumps between gears, the better. Small jumps ensure a smooth transition from gear to gear and make it possible to pedal efficiently by maintaining high cadence at all times.

Cadence is a term referring to the rotations of the cranks per minute. High cadence (e.g., 90RPM) is associated with greater average speed and minimized energy expenditure. (Quote: “Spinning is winning.”)

3. 1x Friendly

10+ speed cassettes with large gears are the norm for 1x drivetrains (the current standard in the MTB world.) The extra gears provide greater range and reduce the downsides of having a single chainring at the front.

Thus, if you want to switch to a 1x drivetrain, big 10+ speed cassettes are a necessity.

What Are The Downsides of Converting to 11-speeds?

There are two notable downsides that come with an 11-speed conversion:

• Pricy

The main obstacle is the price of the components needed for the conversion. As already mentioned, one would have to buy a good number of parts to complete the switch.

And if you don’t want to do the mechanical work yourself, the bill will increase even further.

• Lower tolerance for imperfections

The smaller spacing between the gears reduces the margin for inaccuracy. If you want smooth shifting, you will have to re-adjust the derailleurs and replace components fairly frequently.

Summary: What You Need To Know

1. 11-speed MTB cassettes can be installed on an 8-speed MTB or road hub.

2. An 11-speed road cassette cannot be installed on an 8-speed hub. The hub is too narrow and creates rubbing between the chain and the spokes when riding in the smallest gear.

3. 11-speed MTB cassettes can be installed on an 11-speed road hub with a 1.85mm spacer.

4. A conversion from 8 to 11 speeds requires lots of new parts (cassette, derailleur, shifter, gear cable, chain).

5. The main benefit of 11-speed cassettes is the extra range and the smaller jumps between gears.