Posted at: Jan. 5, 2022
Crank length is a small difference, but it makes a big difference in riding style. In this article, we summarize Shimano's crank length lineup for road cranks and how to find the best crank length.
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The standard crank length for a complete road bike is 170mm or 172.5mm, but there are actually cranks with other lengths.
There are actually other crank lengths available as well. Shimano has a lineup of 8 different crank lengths.
The current model lineup of cranks for road use is as follows.
| Crank | Grade | 160mm | 165mm | 167.5mm | 170mm | 172.5mm | 175mm | 177.5mm | 180mm |
|---|---|---|---|---|---|---|---|---|---|
| FC-R9100 | DURA-ACE | - | ○ | ○ | ○ | ○ | ○ | ○ | ○ |
| FC-R8000 | ULTEGRA | - | ○ | - | ○ | ○ | ○ | - | - |
| FC-R7000 | 105 | ○ | ○ | - | ○ | ○ | ○ | - | - |
| FC-4700 | Tiagra | - | ○ | - | ○ | ○ | ○ | - | - |
| FC-R3000 | SORA | - | ○ | - | ○ | - | ○ | - | - |
| FC-R2000 | CLARIS | - | ○ | - | ○ | - | ○ | - | - |
DURA-ACE has the largest lineup, with seven types of cranks available. As it is the highest racing grade used by professionals, it is likely to fit any rider’s body shape.
On the other hand, for ULTEGRA and lower grades, the maximum size range is four sizes, and fine adjustments are made across the grades.
For example, if you are a short woman, you should choose the 105, which has the shortest crank in the lineup at 160mm.
For example, if you are a short woman, you should choose 105, which has the shortest crank length of 160mm, and if you want to adjust the crank length more finely, you should choose 105 or higher.
In the past, the crank length was considered to be “your height / 10”, but recently, many people seem to be using “(your height / 10) - (2.5 to 5mm)”.
If you are 170cm tall, you should use “165mm or 167.5m”, if you are 175cm tall, you should use “170mm or 172.5mm”, if you are 180cm tall, you should use “175mm or 177.5mm”.
This theory is not necessarily correct, but it can be used as one of the indicators when choosing a crank length.
The problem here is when a woman rides a road bike.
The average height of Japanese women is said to be 159cm, so using the same method of calculation, a 155mm to 157.5mm crank would be optimal, but the shortest crank in Shimano’s lineup is the 105 grade FC-R7000 at 160mm.
In other words, when a woman rides a road bike, she needs to turn the cranks in a larger circle than a man, which puts more stress on her knees and legs.
Therefore, when a woman rides a road bike, she needs to use a lighter front chainring such as outer 46T and lower the overall gear ratio.
The length of the crank is the “radius” of turning the pedals, so if the radius becomes larger, the turning circle becomes larger, and if it becomes smaller, the turning circle becomes smaller.
In fact, crank length also affects the fitting of the entire bike.
For example, if you change from 170mm cranks to 175mm cranks, the top position of the pedals will be 5mm higher and the bottom position will be 5mm lower because the crank length is 5mm longer, which naturally changes the distance from the saddle. The distance between the front and rear of the saddle may also need to be adjusted, as it will be 5mm forward and 5mm back.
If you have ever had a saddle height fitting, you know that a 1cm change in saddle height can make a difference in your riding style, so even a 5mm or 2.5mm change can make a subtle difference.
Generally speaking, it is said as follows.
However, this is a general theory, so it will vary depending on the rider’s leg length and leg quality.
However, it is not absolute to choose the crank according to the theory. In fact, some professional road riders choose the same crank length as the theory, while others choose shorter or longer crank length.
It is best to compare your senses and actual riding data to determine which is best for you, but it is difficult to try out your favorite crank by yourself, so it is best to have a test ride at a sports bicycle store.
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