Mounting an 11-speed Cassette On a 9-speed Hub

A 9-speed MTB hub can accept an 11-speed MTB cassette.

However, a 9-speed Road hub is not compatible with an 11-speed Road cassette.

Requirements for Installing an 11-Speed Cassette on a 9-speed Hub

1. Spacing

An 11-speed cassette will fit on a 9-speed hub only when the hub is wide enough.

Luckily, 8,9,10 and 11-speed mountain bike hubs have the same spacing, and one can therefore use an 11-speed cassette on all of them.

However, 11-speed road cassettes require a wider freehub body in order to get the chain away from the spokes when riding in the lowest gear (largest cog).

The lowest gear on road bikes is much smaller than that of MTBs. (E.g., 28-teeth compared to 35+teeth). The smaller diameter of the largest cog makes it possible for the chain to rub against the spokes.

To prevent this issue, 11-speed freehubs have 1.85mm extra space between the large cog and the hub’s flange. The extra spacing prevents rubbing.

MTB bikes do not have this problem because the largest sprocket is a lot larger and its teeth stand taller and clear the spokes.

The taller the sprocket, the greater the space between its teeth and the spokes because the spokes’ angle gets progressively narrower from the bottom to the top.

FAQ: Why do 11-speed road hubs come with a 1.85mm and 1mm spacer?

11-speed hubs may come with additional spacers to make the hub compatible with MTB and road cassettes of different speeds.

By putting a 1.85mm spacer on an 11-speed road hub, one can install 8/9/10/11 MTB cassettes on the hub.

The 1.85mm spacer is essentially shortening the usable part of the freehub body to the dimensions of an 8/9/10/11-speed MTB hub. Thus, the sprockets end up at the same places where they would be when installed on an MTB hub.

If you use both spacers (1.85mm+1mm), the hub will also become compatible with 10-speed road cassettes.

The extra 1mm is needed to push the 10-speed cassette further away from the spokes.

Note: If you have an 8/9-speed hub, you will only need the 1mm spacer to make the hub operational with a 10-speed road cassette.

Additional Parts Needed for The Conversion

Below are two lists containing the parts needed for a 9-to-11 speed conversion.

Option 1: MTB

If you have a 9-speed MTB and plan to convert it to 11-speeds, you will need:

  • 11-speed cassette
  • 11-speed MTB derailleur
  • New chain (11-speed chains are narrower)
  • 11-speed shifter
  • New gear cable (recommended)

Option 2: Road (road components only)

If you have a 9-speed road bike and plan to turn it into an 11-speed machine, you will need:

  • 11-speed road hub (you will have to replace your wheel or re-lace your existing rim)
  • 11-speed road cassette
  • 11-speed shifter/brifter (this doesn’t apply to people using friction shifters)
  • 11-speed chain
  • New gear cable (recommended)

Option 3: Road (MTB components)

A road bike can be converted from 9 to 11 speeds by using mixed (MTB+road) components too.

By going this route, one can avoid replacing the hub because MTB cassettes have larger cogs that clear the spokes and do not necessitate a new, wider hub.

The needed parts will be:

  • 11-speed MTB cassette
  • 11-speed MTB derailleur (11-speed MTB and road derailleurs have a different rear shift ratio and aren’t interchangeable)
  • 11-speed shifter

This point will be problematic because 11-speed brake-shifters are not compatible with 11-speed MTB derailleurs.

11-speed road shifters pull a different amount of cable per click and won’t move the MTB derailleur as much as required for smooth shifting.

Therefore, this conversion works best when the road bike in question uses flat handlebars.

Another option would be to use 11-speed bar-end shifters or some sort of friction shifters.

  • 11-speed chain
  • New gear cable

FAQ: What is a rear shift ratio?

Rear shift ratio is a term which describes how much a derailleur moves per 1mm of cable movement initiated by the shifter. For example, if a derailleur has a 1.7 shift ratio, it moves 1.7mm per 1mm of cable pulled or released by the shifter.

If two derailleurs have different rear shift ratios, they aren’t interchangeable.

FAQ: What are the benefits of 11 speeds over 9 speeds?

11-speed cassettes have the following advantages over 9-speed models:

  • Larger gears. An 11-speed MTB cassette can have a 42th+ larger cog. Technically, the same applies to some 9-speed cassettes. However, wide-range 9-speed cassettes come with big jumps which make it difficult to maintain optimal cadence smoothly.
  • Smaller jumps. The more speeds there are on a cassette, the smaller the jumps between the gears. Smaller jumps are beneficial because they facilitate the maintenance of optimal cadence.

Cadence is a term referring to the rotations of the cranks per minute. High cadence (e.g., 90rpm) is considered beneficial for maintaining greater average speed with minimal energy expenditure.

Summary: What You Need To Know

  • You can install an 11-speed MTB cassette on a 9-speed MTB hub right away.
  • You cannot install an 11-speed road cassette on a 9-speed road hub because the hub is too narrow and creates a possibility for the chain to rub against the spokes when riding in the largest cog.
  • You can install an 11-speed MTB cassette on a 9-speed road hub.
  • To install an 11-speed MTB cassette on an 11-speed road hub, you will have to use a 1.85mm spacer because 11-speed road hubs are wider.

A conversion from 9 to 11-speeds will give you a greater range and the potential to maintain a higher cadence. However, it’s also a fairly expensive process because you will need a new cassette, derailleur, right shifter, chain, gear cable….etc.

Also, if you have a 9-speed road hub and want to use an 11-speed road cassette, you will have replace the hub too.

This change will require a new wheel or re-lacing of the old. To avoid getting a new wheel, you can use an 11-speed MTB cassette and derailleur, but this route will prevent you from using brake-shifters as 11-speed road shifters aren’t interchangeable with MTB 11-speed shifters.

This Post Has 2 Comments

  1. Chazzo

    Hi Brainy,
    I am looking to convert my old mountain bike to a gravel bike. I have a 135mm Chris King 9-speed rear hub. Can I put an 11-speed road cassette (11-34) and use the Shimano GRX derailleur with Shimano 105 road shifters or will the cassette flat out not fit on the hub?

  2. Ed

    Shimano 11-34 11sp cassette fits on a 9 or 10 speed hub because the 34t cog is dished out beyond the freewheel and towards the spokes.

Leave a Reply