How to Measure Crank Arm Length?
Crank length significantly influences a rider’s biomechanics; a bad-fitting crank can detrimentally affect performance or can even lead to injuries for the rider.
What is Crank Length?
Crank length is the distance from the center of the bottom bracket (where the crank arms attach to the bike) to the center of the pedal spindle.
Why is Crank Length Important?
This measurement is crucial because it affects the rider’s leg extension, pedaling efficiency, and overall comfort while riding. Having the right crank arm length is very essential for optimizing your ride quality.
In addition to rider fit concerns, longer crank arm length may also elevate the likelihood of toe overlap and pedal strike. This is especially true for smaller frames and more aggressive frame geometries where wheelbase is shorter.
What is the Best Crank Length?
The majority of the bicycle industry specifies proportional length crank arms that are reduced in size on smaller bikes and increased in size on larger bikes. Standard lengths for production bicycles generally fall between 165-175mm, though both shorter and longer cranks can be found in aftermarket options. So it’s not a one-size-fits-all situation, and the best crank length depends on several factors including:
- Rider Height: Taller riders may benefit from longer crank arms, while shorter riders may find shorter cranks more comfortable.
- Leg Length: The length of the rider’s legs can also influence the optimal crank length
- Riding Style: Different types of cycling (e.g., road cycling, mountain biking, track cycling) may require different crank lengths for optimal performance.
- Flexibility and Comfort: Some riders may prefer shorter cranks for a more comfortable pedaling motion, especially if they have limited flexibility.
However, there has been a tendency in Pro Cycling of switching to shorter cranks, for example Tadej Pogačar uses 165mm but this doesn’t mean it’s the best for everyone. It’s essential to consider personal comfort and biomechanics when selecting crank length.
How to Measure Crank Arm Length?
- Tools Needed: You will need a ruler or a measuring tape that can measure in millimeters for accuracy.
- Locate the Bottom Bracket: Find the center of the bottom bracket where the crank arms attach to the bike frame.
- Measure the Crank Arm: Place the ruler or measuring tape at the center of the bottom bracket and extend it to the center of the pedal spindle (the point where the pedal attaches to the crank arm).
- Record the Measurement: Note the distance in millimeters. This is your crank arm length.
- Repeat for the Other Side: Measure the other crank arm to ensure both sides are the same length, as they should be.
How to Choose the Correct Crank Arm Length?
This definitely is not in my area of expertise, and I would definitely recommend consulting with a professional bike fitter or a knowledgeable bike shop for best results.
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