What crank length do most bikes come with?

Most road bikes ship with 170 mm or 172.5 mm cranks. By the inseam × 2.16 formula used here, that corresponds to an inseam of roughly 78-80 cm. The × 2.16 figure (Lennard Zinn upper bound) tends to recommend a longer crank than many fitters now prefer — there is a strong trend towards shorter cranks, so do not be surprised if a 170-172.5 mm crank feels right even at a slightly longer inseam.

Does crank length really matter?

For most riders, the difference between 170 mm and 172.5 mm is negligible. However, very short or tall riders can benefit significantly from correct crank length, especially for comfort and injury prevention.

Should I go shorter or longer?

There is a trend towards shorter cranks, especially for time trials and triathlons, as they allow a more aerodynamic position. Shorter cranks also suit riders with hip flexibility issues.

BikeCalcs

Crank Length Calculator — Optimal Crank Arm Length

Find the optimal crank length based on your leg length.

Inseam Length

Inseam (cm): barefoot, feet ~15 cm apart, measure floor to crotch with a book spine pressed firmly up against your pubic bone.

How We Calculate This

Crank Length Formula

Crank Length (mm) = Inseam (cm) × 2.16

This is Lennard Zinn's leg-length-proportional upper bound (inseam in mm × 0.216). The result is rounded to the nearest real manufacturer crank length — 160, 162.5, 165, 167.5, 170, 172.5, 175, 177.5 or 180 mm — since Shimano, SRAM and Campagnolo sell cranks in 2.5 mm increments across this 160-180 mm window.

Frequently Asked Questions

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Last updated: 2025-02-20

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.