Can I Use An MTB Crankset On A Road Bike?

ByLouis Reading Time: 6 minutes

One of the best aspects of cycling as a sport and hobby is the amount of customization you can do to a bike.  My brother built his carbon steed bit by bit as he found components on sale.  But what about mixing your road bike with MTB parts?  For example, can you use an MTB crankset on your road bike?

MTB pedals are further apart than road bike pedals.  This means that the spindle or the crank-axle is longer.  So, to fit an MTB crankset to a road bike, you need to use spacers in your bottom bracket.  You may also need to change your front derailleur and shifter.

In short, it is possible to put an MTB crankset on your road bike, but the process is not without its challenges and infuriating red tape.  Depending on your particular frame and crankset, these challenges could range from negligible to insurmountable.

Putting An MTB Crankset On A Road Bike

There are several motivations for putting an MTB crankset on a road bike.  For example, many people who tour prefer to use MTB cranksets.  However, in some cases, it could be that you are building a bike and have an MTB crankset on hand.

The Differences Between MTB And Road Cranks

There may only be a few minor differences between MTB and road cranksets.  Still, in cycling, little differences can have significant impacts.

Firstly, MTB crank spindles are longer.  Because MTBs are generally higher off the ground, the rider needs to stand a little wider for stability.  This means that the pedals must be slightly further apart.

To achieve this, the “axle” between the pedals, known as the spindle, is longer. 

Secondly, MTB cranksets tend to be stronger because MTBs typically take more of a beating than road bikes.  With that strength, you can also expect them to be typically heavier than road cranksets. 

Finally, and most importantly, MTB cranksets generally have smaller chainrings than their road bike cousins. 

The vast majority of riders who deliberately choose MTB cranksets do so for these smaller chainrings.  This is also why MTB cranksets are popular among tourers.  The smaller chainrings alter the gear ratio, making pedaling easier, albeit slower. 

Because tourers carry a lot of baggage, the more manageable gear ratio is a welcome compensation for the heavier weight.

The Challenge Of Making An MTB Crankset Fit A Road Bike

While you may want to use an MTB crankset to benefit from the differences, those very same differences can make it a headache to install the crankset on a road bike frame.  There are three challenges that you will need to overcome.

Challenge One – Attaching The Crankset To Bike

The first and most obvious challenge is fitting the crankset onto the bike.  And this challenge relates to your bike’s bottom bracket.  The bottom bracket is the bearing unit that hugs the spindle and allows the cranks to turn. 

Unfortunately, as most cyclists can attest, there are way too many bottom-bracket standards for MTBs and road bikes. 

If your road bike uses a threaded bottom bracket that screws in, you will need an MTB threaded bottom bracket to accommodate your crankset. 

Obviously, the bottom bracket will be longer than the frame allows.  Still, this problem is quickly resolved with the set of spacers on either end. 

The same applies if your bike uses a press-fit bottom bracket.  Press-fit bottom brackets are sealed bearing units pressed into the frame using a unique tool.  In this case, you will need to get an MTB bottom bracket and fit it to your frame using spacers. 

Some low-end bikes use square taper bottom brackets where the cranks are screwed into a spindle.  If you have a bike with a square taper bottom bracket and square tapered MTB cranks, you simply need to screw the cranks to the spindle. 

This is obviously the easiest solution, but if you are building a mid to high-end bike, it’s doubtful that you will use a square tapered bottom bracket.

Challenge Two – Positioning The Front Derailleur

Your second challenge is to get the front derailleur in the correct position.  With your MTB crankset now in place, two significant changes have occurred.  Firstly, your chainrings are now slightly further away from the frame.  Secondly, your chainrings are a lot smaller. 

This means that your front mech (derailleur) will be too high and need to be lowered. 

Lowering your front mech is relatively simple if it has a clamp-on mounting system.  In this case, you simply loosen the clamp, move the mech down and then tighten the clamp again. 

However, if your derailleur is a braze-on model, it is fitted to a specific place on the frame, and there is no way of lowering it.  So, unfortunately, your MTB crankset journey ends here if this is the case.

If you are not so unlucky and have managed to get your front mech into place, you now have a second challenge.  Your derailleur must reach out further to get over the chain, which is now further away. 

Unfortunately, in most cases, this problem is only resolved by actually replacing the front mech with an MTB derailleur.  This is because MTB mechs can reach out quite a bit further than road mechs. 

Challenge Three – Indexing The Gears

With your front mech in place, you are ready to move on to the last hurdle, which is to index the gears.  However, here again, you could be faced with multiple stumbling blocks.

The first and biggest challenge relates to the shifter.  Road and MTB shifters are not indexed the same.  In other words, the distance that shifters move the derailleurs are different.  If you are very lucky, your shifter will work OK and be able to shift front gears easily. 

However, in most cases, you should also change the shifter.  Unfortunately, it is added cost, but it also means that you are less likely to encounter gearing frustrations on your journeys. 

If you don’t want to change shifters, a second option is to use a “1x” drive train.  These common MTB drive trains use only chainring, completely removing the need for a front shifter and derailleur.  Obviously, the downside is that it also limits your total gear ratio.

You may also have difficulty indexing your rear gears because the chain angle has changed.  In most cases, it is resolved by just re-indexing your gears, but for a few unlucky riders, it also meant having to change the gears and shifters at the back. 

If you are dead set on having more than one chainring, opt for two at most.  As soon as you put three rings up in front, your gearing will become highly temperamental.

Conclusion

While putting an MTB crankset on a road bike is possible, the process has several challenges.  Firstly, you will likely need to change the bottom bracket to accept the longer spindle.  You may also need to get a new front derailleur and gear shifter to get your front gears to index consistently.

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