Crank length, honestly

Walk into most shops and you'll leave with 172.5 mm cranks. Not because they measured you — because that's what came on the bike.

What crank length actually does

A longer crank gives you leverage; a shorter one gives you clearance and cadence. At the top of every pedal stroke your knee and hip fold — the longer the crank, the tighter that fold, several thousand times an hour. Ride in an aero position and the fold gets tighter still, which is why the short-crank trend started in triathlon: shorter cranks open the hip angle, and an open hip holds aero longer without your knees arguing with your chest.

The starting point

The formula fitters actually start from is inseam-indexed: roughly your inseam in centimeters × 2.16, in millimeters. An 80 cm inseam lands near 172; a 74 cm inseam near 160. Riding triathlon or time trial? Take about 5 mm off. Gravel? A touch shorter helps with ground strikes and higher cadence. The fit room runs this for you in ten seconds.

The catch the industry built

For years the big brands machined 170 to 175 and little else — so shops fit riders to the parts, not parts to the riders. If your number comes back 160 or 155, you weren't wrong; the catalog was. It's one reason we carry OVERFAST, one of the few houses anywhere machining lengths from 155 mm — with published weights and tolerances, because numbers you can't check are marketing.

What to do with your number

A formula gets you to the neighborhood; a fitting gets you to the door. Run your measurements, then book a fitting if you're between sizes or changing position — the fee is credited against your purchase. Then build the bike around it, not the other way around.

Systems of uncommon velocity.