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Condensed answer: Some mountain bike cassettes can be installed on road bikes. However, a few variables have to be taken into consideration for the set-up to work.

How Does A Geared Bicycle Shift?

Before continuing with niche down information, a generic explanation of the index shifting process is in order.

Here’s how index shifting happens:

1. The rider presses or pulls the shifter.

2. The shifter pulls or releases a pre-determined amount of cable.

3. The jockey wheels of the rear derailleur move either to the left or right and bring the chain onto a new cog.

On the surface, the process is incredibly simple, but many technicalities have to be respected to ensure smooth shifting.

Important Terms

The list below contains cycling tech terms that make it easier to understand the matter.

1. Cable pull

Index shifters pull or release a pre-determined cable length known as cable pull.

The cable pull is a constant. In consequence, the rest of the system (cassette+rear derailleur) is designed to work with a specific cable pull and malfunctions when the value is changed.

2. Rear shift ratio

To ensure smooth operation, derailleurs have a specific rear shift ratio.

The rear shift ratio is presented as a single number and signifies how much the rear derailleur moves per mm of cable pull.

For example, a Shimano 9-speed derailleur has a 1.7 rear shift ratio. This means that the derailleur moves 1.7mm for every millimeter of cable movement.

3. Cog Pitch

Cog pitch is the center to center distance between two adjacent cogs on a cassette.

This measure is very important. A cog pitch different than the number that the derailleur and the shifter are engineered for would result in poor shifting.

For example, the cog pitch of a Shimano 10-speed MTB cassette is about 4mm.

If you take that cassette and put it on a bike with an 8-speed shifter, the shifting will be all over the place because the cogs wouldn’t be where the derailleur “expects” them to be.

Can You Put a Mountain Bike Cassette On a Road Bike?

The basic theory is covered. Now it’s time for the main topic at hand, namely fitting a mountain bike cassette on a road bike.

To determine how this can be done, we need the following data:

1. The rear shift ratios of the derailleurs

2. The cable pull of the shifters

3. The cog pitch of the cassettes

Note: Since Shimano and SRAM are the two most popular producers of mountain bike cassettes, the focus will be on them.

Table A1: Shimano Derailleurs

The rear shift ratio of Shimano road and MTB derailleurs is the same (1.7) up until 10 speeds.

At that point, the rear shift ratio of road derailleurs remains 1.7, but that of MTB derailleurs changes to 1.2.

The data results in the following conclusions:

• 6,7,8, 9-speed MTB/Road Derailleurs + 10 Speed Road derailleurs move the same amount per millimeter of pulled or released cable.

The next important piece of data is the cable pull of the shifters.

You can find in the table below:

Table A2: Shimano Shifters Cable Pull

Findings:

• The cable pull ratio of Shimano shifters is the same up to 9 speeds.

Final Conclusion For Shimano Cassettes

A mountain bike cassette can work on a road bike only if it has the same cog pitch as its road equivalent.

If the cog pitch is different, the shifting would be inaccurate.

The formula for calculating the cog pitch is:

Cog Pitch = Cable Pull x Rear Shift Ratio

Two cassettes can have an identical cog pitch only when they’re designed for derailleurs with the same rear shift ratio and shifters with the same cable pull.

In Shimano’s case, this condition is met only on 6,7,8, and 9-speed drivetrains.

Shimano’s 10-speed road rear derailleurs have the same shift ratio as 6,7,8 and 9-speed MTB derailleurs. As a result, you can combine an 8 or 9-speed MTB derailleur with a 10-speed road cassette.

However, you can’t use a 10-speed MTB cassette on a road bike because the cog pitches of 10-speed MTB and Road Cassettes are different.

Table B1: SRAM Derailleurs

Findings

• 10-speed road and MTB Exact Actuation SRAM derailleurs have the same rear shift ratio
  
• 11-speed road SRAM derailleurs have the same rear shift ratio as 10-speed road and MTB Exact Actuation derailleurs

Table B2: SRAM Shifters Cable Pull

Final Conclusion For SRAM’s Cassettes

SRAM cassettes designed for 10-speed exact actuation MTB and Road derailleurs have a matching cog pitch (3.1×1.3=4.03).

Therefore, SRAM’s 10-speed MTB and Road cassettes are interchangeable when used with SRAM components.

SRAM’s 11-speed road cassettes have the same cog pitch as SRAM’s 10-speed MTB and Road cassettes

However, SRAM’s 11-speed MTB cassettes have a different cog pitch than 11-speed Road Models, and the two aren’t interchangeable.

The Maximum Capacity of the Derailleurs Matters Too

An MTB cassette may have the necessary cog pitch to be operational on a road bike, but the combo may still fail because the derailleur doesn’t have the capacity to reach all cogs.

MTB cassettes have lower gearing than road models. And with the rise of 1x drivetrains’ popularity, one can find 9 and even 8-speed cassettes with 40+ teeth on the largest cog.

It goes without saying that such a cassette would not fit on your typical road bike without modifying the drivetrain.

How Can I Use a Large Capacity MTB Cassette On a Road Bike?

If your current road derailleur cannot cover the MTB cassette that you want to fit on it, you have the following options:

1. Use a derailleur hanger extender

Hanger extenders are small pieces of aluminum that attach to the original derailleur hanger and lower the derailleur to increase its range.

2. Switch to an MTB derailleur

6-9-speed MTB derailleurs are compatible with up to 10-speed road shifters except for the Tiagra 4700 series.

If you have 10-speeds or under, you can simply switch to a wide range 9-speed MTB derailleur. If you want to learn more on the topic, consider reading this post.

FAQ: Are there any benefits to using an MTB cassette on a road bike?

There are two:

1. If you already have a compatible MTB cassette, you can save some money.

2. If you want to extend the gear range of your bike, you can do so by installing an MTB cassette.

Are there pro road cyclists who use MTB cassettes?

Yes. The super successful British cyclist Bradley Wiggins relied on a long cage derailleur (Shimano di2) and wide range MTB cassettes. The extra gearing allowed him to climb without having to ride out of the saddle unnecessarily.

Friction Shifting Makes Almost Everything Compatible

A friction shifter doesn’t work with clicks pulling or releasing a pre-determined amount of cable. The shifter is “free”, and the user moves it as much as necessary to make a shift.

As a result, the rear shift ratio of the derailleur becomes inconsequential.

Friction shifting allows bikers to mix road and mountain bike components of all kinds. Hence why friction shifters are so popular among touring cyclists.

If you have a friction shifter on your road bike, you can use any MTB cassette that meets the following criteria:

• The cassette fits on the hub.
  
• The cassette doesn’t exceed the maximum capacity of the rear derailleur.

Flat Bars = Possibility For MTB Shifters

If your road bike has flat bars or risers, you can install MTB shifters on it.

This change will greatly increase the number of MTB cassettes that the bike can accept.

Summary

• Shimano’s 6,7,8 and 9-speed MTB cassettes can be used on road bikes that could accommodate such cassettes.
  
• SRAM’s 10-speed MTB cassettes can be used on road bikes with 10-speed SRAM shifters designed for exact actuation derailleurs.
  
• Friction shifters allow you to use almost every MTB cassette that would fit on your road hub.
  
• In all cases, the derailleur of your road bike should have the capacity to cover the entire cassette. Large MTB cassettes are incompatible with short cage road derailleurs.