A pro mountain biker wants to modify his bike according to his needs. Like other parts of the bike, the crank arm is also an important part as it helps in increasing acceleration and keeping the bike stable. That’s why many cyclists want to know if the crank arms are universal or if there is some possibility of modification.

You can easily replace the chainring on a crankset, but most of the time the crank arm replacement process is not that simple. But the good news is that most cranksets these days have the option of replacing the arms. Since crank arms are not universal, you may also get better performance by replacing them.

In this writing, I will present some information regarding mountain bike crank arms. Please read this article even if you have no plans to change the crank arm because this will help you rethink crank arms.

What Is A Mountain Bike Crank Arm?

The crank arm is the two extended arms of the crankset to which the pedals are attached. Along with the changes in the cranksets of modern-day mountain bikes, there have also been many changes in the arms in them. Because Crank arms vary in length or design to suit different riders or tracks.

The rider can use a relatively short or large crank arm on his mountain bike crankset considering his height, facility, and track condition.

  • Longer crank arms provide a slower, larger circular pedaling path. These allow the rider to apply more force per inch to gain speed.
  • Shorter crank arms with the best crankset, on the other hand, provide a shorter circular pedaling path at faster speeds. A rider can exert relatively less force per inch to achieve speed. Both types of crank arms offer advantages for different riders.

Are Mountain Bike Crank Arms Universal?

No, mountain bike crank arms are not universal. Thus different mountain bike crankset sizes are available with different crank arms. Although companies use a 175mm crank arm length on most adult bikes, where crank arm lengths on children’s or women’s bikes are typically 165mm. But most times, the rider can choose the crank arm length between 165mm to 180mm according to his convenience.

The design of crank arms also varies with different bikes or cranksets. If you look at the crank arms of the Shimano crankset and the HOPE Evo crankset, you will see the difference in design. Moreover, you can notice the change in the design of the crank arm with the design of the complete set.

Different companies use different materials to make the crank arms of their mountain bikes. And, most bikes today use carbon fiber or aluminum crank arms. But you will often spot steel crank arms on cheap MTB.

Does Crank Arm Length Really Matter For Mountain Biking?

No, crank arm length is not so important for mountain biking. You may have noticed that most mountain bikes come with 170mm or 175mm crank arms.

Most riders don’t even care much about this length, but pro riders are sometimes more conscious about the crank arm and want to replace the crank arm for better performance.

Many people think longer crank arms provide more leverage, which allows the rider to apply more force to the pedals. But actually smaller cranks are more convenient for most riders. One study found that 145 and 170mm cranks produced more power than 120 and 220mm cranks. And, other studies also show that differences in crank length have little effect on rider performance.

  • However, a longer crank arm may be more comfortable for a taller rider.
  • Slightly shorter crank arms can help with acceleration and fit the bike better. In addition, shorter crank arms are less likely to rub against the trail when riding rough tracks.

Why Are Mountain Bike Crank Arms So Long?

When you are riding a road bike, relatively short crank arms will be helpful to you. Shorter crank arms are more suitable, especially for cornering. But the situation is slightly different with mountain bikes as the stability of the bike is more important than cornering for riding an MTB.

Since mountain bikes require you to ride uphill or on rough roads, a longer crank arm gives the rider some advantage ‍as they provide more stability. On the other hand, large crank arms are also useful when riding down hills. Because of this, mountain bikes may have a slightly longer average crank arm length than other bikes.

Final Words

As a rider, you want to have the best control over the bike while riding. Besides, you want your mountain bike to be as comfortable and efficient as possible. That’s why many riders add or replace many things on their bikes to accomplish these goals.

Although crank arm length won’t help you much for riding fast, you’ll prefer stability over speed on mountain bikes. And now you realize that Mountain bike crank arms are not universal; so you can replace them according to your height. Perhaps this replacement will provide you with a more comfortable riding experience on the trail.