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A while back I asked myself – what would be the cheapest way to add brake-shifters (the type of shifters found on road bikes) to an MTB?

My instinctive reaction was to find a set of solid and affordable road shifters compatible with a basic MTB rear derailleur.

Shimano Claris made the most sense.

So, how can all of this work?

There are two requirements for a set of shifters to be integrated into a new drivetrain:

• They have to match the number of gears on the cassette.
• The cable pull of the shifters and the shift ratio of the derailleurs have to agree when combined in the specific drivetrain.

The first requirement is obvious. If you have an 8-speed cassette, you need an 8-speed shifter. If the shifter is designed for fewer speeds, then you can’t use all the gears. If the shifter is designed for more speeds, you will have what’s called a ghost shift. Both situations are not ideal.

The second requirement is a bit more complex, but I will try to explain it as concisely as possible.

Cable Pull and Rear Shift Ratio

• Shifters control derailleurs through gear cables (unless the shifting is electronic). When a shifter pulls the gear cable, the rear derailleur moves inward (towards the bike). When the shifter releases the gear cable, the derailleur returns to the previous position.

• The amount of cable pulled or released by the shifter is known as cable pull.

• The value of the cable pull depends on the number of gears (e.g., 8, 9…etc.), the bike type (road, MTB…etc.), the brand, and the specific sub-category of the shifter. Two shifters made for the same number of gears by the same manufacturer could have a different cable pull. Example: Tiagra 4700.

• The rear shift ratio is a property of the rear derailleur that indicates how much the derailleur moves inward or outward per 1mm of cable pulled or released by the shifter. For example, if the rear shift ratio is 1.7, then the derailleur would travel 1.7mm per 1mm pulled by the shifter.

• The cable pull combined with the rear shift ratio results in predetermined and controlled movement of the derailleur across the cassette.

• If the values of either property are incorrect for the particular drivetrain, the derailleur will not move to the right location, and the shifting experience will be far from ideal.

Once you know those technical details, it becomes fairly easy to come up with unusual drivetrain combinations.

Installing a Claris Rear Shifter On an MTB

• Claris is an 8-speed Shimano groupset and can therefore only be installed on 8-speed drivetrains.

• The cable pull of Shimano’s 8-speed road and MTB shifters is the same – 2.8mm.

• The rear shift ratio of Shimano’s 8-speed road and MTB derailleurs is also the same – 1.7.

• Consequently, you can install a Claris rear shifter on an 8-speed MTB equipped with a Shimano 8-speed rear derailleur right away.

• You can also use a 9-speed Shimano MTB derailleur as those have the same rear shift ratio as 8-speed models. If two derailleurs have the same rear shift ratio and are capable of covering the cassette that you’re going to use, they’re interchangeable.

• The advantage of going with a 9-speed derailleur is that some of them are of better quality than the 8-speed models.

Below is a small table that contains the rear shift ratios and cable pulls of Shimano’s derailleurs and shifters.

Conclusion: A Claris rear shifter can be installed on an 8-speed MTB using an 8 or 9-speed Shimano rear derailleur right away.

Installing a Claris Front Shifter On an MTB

Claris front shifters can’t be directly installed on an MTB drivetrain because front MTB and road derailleurs have different shift ratios.

Why?

• MTB front shifters have significantly more leverage (not always but often) and thus have a longer cable pull than road front shifters by a few millimeters.

• If an MTB front derailleur is combined with a Claris front shifter, the shifter won’t move the derailleur sufficiently for a jump between the chainrings to occur.

• In the opposite case (road front derailleur + MTB front shifter), the shifter will “over-shift” or in other words, the derailleur will move past the desired cog.

There are also architectural differences between MTB and road derailleurs. For instance, MTB derailleurs have a shorter cage since they don’t have to operate with very large chainrings.

The cage of road derailleurs is longer so that it can effectively move and guard the chain when operating with large road bike cahinrings.

This front incompatibility leaves the following options:

• Run a 1x drivetrain

If you run a single chainring at the front, front-end compatibility becomes irrelevant from the perspective of the mech.

A 1x drivetrain will require the following parts:

1. A narrow-wide chainring (for better chain retention)
2. A shorter chain
3. Larger cassette (to make up for the lack of low gears caused by the absence of a small chainring)
4. New derailleur or a derailleur hanger extender if the current model can’t reach the largest cog on the new cassette.

• Separate Friction Shifter

Another underrated option is to use a friction shifter of some sort for the front derailleur.

Unlike indexed shifters, friction models don’t have segregated movement and audible clicks. The shifter moves as much as the rider wants it to move. Consequently, cable pull values and shift ratios become irrelevant.

The downside is that shifting is no longer automatic and you have to be more cautious. However, front friction shifting is much easier because the spacing between the chainrings is fairly large and there are fewer jumps to make. Thus, you don’t have to be as accurate.

For a long time after the invention of indexed shifters road cyclists continued to use a friction shifter for the front to save weight and make trimming of the front derailleur easier. (In a few words, trimming is the act of moving the derailleur’s cage ever so slightly so that the chain doesn’t rub against it.)

Note: There are two types of front friction shifters that can be used in this case:

• А bar-end shifter (a good choice for drop bars)

• A thumb shifter

• Keep using an MTB shifter

The cheapest solution would be to keep using the existing MTB shifter for the front derailleur.

The downsides of this approach are:

Handlebar clutter. The cockpit area will look “busy”. If you’re after clean aesthetics, you may not like the outcome.

Installation issues. Drop bars have a 23.8mm diameter whereas MTBs have а 22.2mm handlebar diameter at the shifter area. The shifter’s clamp reflects that. Consequently, if you want to install MTB shifters on a set of drop bars, you will have to file the inner side of the shifter’s clamp, or else the unit won’t fit.

A Note On Brakes

Last but not least, Claris brake-levers are not compatible with standard MTB brakes (V-brakes and mechanical disc brakes.)

Why?

Glad you asked.

It’s because road bike levers are designed for “short pull” brakes where MTB levers operate with “long pull brakes” such V-brakes and mechanical disc brakes. The difference between road and MTB levers comes from the dissimilar leverages of both systems.

I explain in detail the principal of mechanical advantage when it comes rim brakes in this post. So, check it out if you want to learn more.

So, what kind of brakes can you use?

In this case, we have an MTB frame. Thus, the only shortp ull brakes that you can install on it are

• Cantilever brakes
• Mini V-brakes

You can use caliper brakes for instance because the frame won’t have mounts for them.

If you plan on running wide MTB tires, mini V-brakes won’t cut it due to their small clearance. In that situaiton, cantilever brakes are your only option.

Why would you want to do all of this?

• Drop bar switch

The main incentive to use Claris shifters on an MTB is to turn a retro MTB model into a gravel bike with drop bars.

Another option is to simply experiment. E.g., Install drop bars on an MTB with suspension.

Obviously, the first idea is a lot more common.

What are the downsides?

At their core, MTBs aren’t designed for drop bars and unless you get a small frame, you will feel too stretched out. Why? Because MTBs have longer effective top tubes than road bikes.

And when you add drop bars on an MTB frame, you stretch yourself even more and the fit is just off.

This outcome can be remedied to a degree via a smaller frame and a shorter stem. That said, every setup is different and no one can guarantee that your new bike will be comfortable. Hence the reason to put similar conversion into the experiment category.