"Use 172.5 mm" is the default advice and it's wrong for most riders. Crank length should be tied to your inseam, hip mobility and discipline — short riders with limited mobility often do better on shorter cranks; tall flexible riders often prefer longer ones. This calculator picks a length and explains the why.
Crank length affects leverage, cadence efficiency, and hip joint range of motion. Longer cranks give more torque per stroke but require more hip flexion at the top of the pedal stroke — which can hurt riders with limited mobility. Shorter cranks allow higher cadence and reduce hip stress but require more leg speed for the same power.
The 172.5 mm default exists because it's a middle ground. Riders outside the middle benefit from a length that's actually matched to their body.
Only if you have a specific reason — knee pain, hip impingement, or a clear biomechanical goal. 172.5 mm is a fine default for most riders in the 170-185 cm range.
Marginally. At the same cadence, longer cranks produce higher speed because each pedal stroke covers more distance. For most recreational riders this difference is unnoticeable.
Q-factor (stance width) is separate from crank length but matters similarly. If your knees bow out or in at the bottom of the stroke, Q-factor is the place to look.
This calculator was built to answer a question most online versions skip or oversimplify. It runs entirely in your browser; no inputs are stored or transmitted. The math is grounded in standard cycling physics and physiology models, and is suitable for hobbyist and intermediate training use. It is not a substitute for a coach, sports scientist, or professional bike-fit service.
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Children under 13 are not the intended audience.
This calculator is provided for general informational and educational purposes only. It is not medical, mechanical, or legal advice. Predicted values depend on inputs you supply and simplified physical models; real-world outcomes vary. Use at your own risk. Brand names are descriptive only and do not imply affiliation.