Condensed Answer: If the user relies on index shifting, road shifters can be combined with MTB derailleurs when the transmission has up to 9 speeds. A 10-speed road drivetrain can also be combined with an MTB derailleur designed for 9 or fewer speeds.
The road shifters should match the number of gears on the cassette when using index shifting.
If the user relies on friction shifters, they will be compatible with all MTB derailleurs that can cover the entire cassette.
To understand how road shifters can be combined with MTB derailleurs and cassettes, one has to become familiar with the following definitions:
Modern shifters are indexed. This means that each click of the shifter pulls or releases a pre-determined amount of gear cable. This is done to simplify the shifting process by limiting the needed input from the rider. If you want to shift, all you have to do is trigger a single click.
Rear Shift Ratio
The rear shift ratio describes how much a derailleur moves per 1mm of cable pulled or released by the shifter. The rear shift ratio of derailleurs varies with the number of gears that the bike has.
If a derailleur has a 1.7:1 rear shift ratio, the derailleur moves 1.7mm per 1mm of cable pulled or released by the shifter.
The rear shift ratio is crucial when determining compatibility between road and MTB parts.
Friction shifters are old-school. They don’t pull or release a pre-determined amount of cable. Instead, the user moves the shifting lever as much as needed to make the desired shift. In essence, friction shifters are the equivalent of a manual car whereas indexed shifters are an automatic.
The advantage of index shifters is that the rear shift ratio of the used derailleur becomes irrelevant because the user can freely manipulate how much the derailleur moves via the shifter lever.
Combining Road Shifters with MTB Derailleurs and Cassettes
If you plan on using friction shifters, any derailleur that can cover the cassette will operate with the system. This is the main advantage of friction shifters.
That said, friction shifters have the following cons:
- Instability (The user has to move their hands away from the bars because friction shifters do not come in a format combined with the brake levers. The most common friction shifters types are downtube shifters and bar-end shifters.)
- Complicated for Beginners (An uneducated beginner will have a hard time dealing with friction shifters.)
Modern road bikes use brake-shifters a.k.a. brifters. Brake-shifters combine a brake lever and an index shifter in one unit designed specifically for drop bars.
For that reason, indexed road shifters can be used only with MTB derailleurs that have a rear shift ratio matching that of the corresponding road derailleur.
For example, if the bike has a 10-speed cassette and road shifters, it will be compatible with an MTB derailleur that has the rear shift ratio of a 10-speed road derailleur.
If this condition isn’t met, the shifter will not move the derailleur as much as necessary for a shift or a downshift, and the chain will fail to go onto the targeted cog.
The rear shift ratio of 10-speed MTB Shimano derailleurs is 1.2 whereas the rear shift ratio of 10-speed Shimano road derailleurs is 1.7.
The cable pull of a 10-speed road shifter is 2.3mm.
One click of the shifter would move the 10-speed MTB derailleur only 2.76mm. The same click, on the other hand, will move the original road derailleur 3.91mm. Therefore, a 10-speed MTB derailleur won’t be moving sufficiently when used with a 10-speed road shifter.
There are two ways to solve this issue.
The first one is to replace the road shifter with an MTB one. A 10-speed MTB shifter has a 3.4mm cable pull and will therefore move the same derailleur 4.08mm – a number that’s fairly close to the required 3.91mm of travel.
However, in this case, we want to keep the road shifter. Thus, the only solution is to replace the derailleur.
Luckily, 6 to 9-speed Shimano MTB derailleurs and 6 to 10-speed road derailleurs use the same rear shift ratio (1.7). Thus, you will be able to combine a 9-speed MTB derailleur with a 10-speed road shifter as long as the derailleur can cover the entire cassette.
|Number of Speeds||MTB Rear Shift Ratio||Road Rear Shift Ratio|
|8||Shimano – 1.7||SRAM – 1.1||Shimano – 1.7||Campagnolo – 1.4|
|9||Shimano – 1.7||SRAM – 1.1||Shimano – 1.7||Campagnolo – 1.5|
|10||Shimano – 1.2||SRAM – 1.3||Shimano – 1.7||Campagnolo – 1.5||SRAM – 1.3|
|11||Shimano – 1.1||SRAM – 1.12||Shimano – 1.4||Campagnolo – 1.5||SRAM – 1.3|
The table above contains the rear shift ratio of many road and MTB derailleurs.
Another requirement for successful pairing is to match the number of gears with the number of speeds that the shifter is designed for. For example, if the cassette has 10-cogs, the shifter should be designed for 10-speeds too.
This is necessary because the cable pull of the shifters varies with the number of gears. Also, if you rely on a shifter that’s designed for fewer speeds, you won’t be able to use all the gears that the cassette has to offer.
Below is a table containing the cable pulls of different shifters sorted by brands and the number of gears:
|Number of Speeds||Type||Cable Pull|
|6||Road + MTB||3.2|
|7||Road + MTB||2.9|
|8||Road + MTB||2.8|
|9||Road + MTB||2.5|
|Number of Speeds||Type||Cable Pull|
|Number of Speeds||Type||Cable Pull|
|10||MTB + Road||3.1|
FAQ: Are road and MTB cassettes interchangeable?
MTB and road cassettes up to 10 speeds made by the same brand are interchangeable and many consider the terms “road” and “MTB” marketing specifications rather than a necessity.
Thus, one can use a 10-speed MTB cassette on a 10-speed road bike as long as the derailleur can climb all the way to the final cog.
Since road bikes use higher gears, many road derailleurs are too short to cover a wide range 10-speed MTB cassette. Or in other words, the cassette may be compatible, but the MTB version will require an MTB derailleur too.
Since 10-speed MTB derailleurs are not compatible with indexed 10-speed road shifters, it will be necessary to use a wide range 9-speed MTB derailleur.
11-speed MTB and road cassettes are not directly interchangeable. 11-speed road hubs are wider than 11-speed MTB hubs.
The purpose of this modification is to push the largest cog of the 11-speed road cassette further away from the spokes. Road bikes use higher gears, and the largest cog on the cassette could come in contact with the spokes without this change.
MTB cassettes do not have this problem because the lowest gear is bigger and thus the periphery of the big cog is further away from the hub and the narrowest part of the spokes.
Therefore, an 11-speed MTB cassette is too narrow to cover an entire 11-speed road hub. This problem can be circumvented by installing a 1.85mm spacer on the hub before sliding on the cassette.
The Pros of Combining Road Shifters With MTB Derailleurs and Cassettes
- Parts recycling
If you already have MTB parts that would fit within a road system, recycling them would save you money.
- Greater Range
The main advantage of MTB cassettes and derailleurs is that they offer a greater range of lower gears that road components cannot match. Therefore, if you want some extra low gears on your road bike, MTB cassettes and derailleurs will provide that opportunity.
The Cons of Combining Road Shifters and MTB Derailleurs
- Compatibility Issues
The downside of this combination is the great possibility of compatibility problems. Even if all precautions are taken, each set-up is unique and there is always a chance that a small, unexpected problem will occur here and there.
- Labor Intensive
If you’re not a bike mechanic, the conversion could seem difficult to execute on your own. That said, there are plenty of videos online that will greatly facilitate the task.