Maximal cycling power changes by only about 4% across crank lengths from 120 to 220 mm; the standard 170 mm does not substantially compromise power, and optimal cadence falls as the crank gets longer
Key Findings
Maximum power ranged only from 1149 W (220 mm cranks) to 1194 W (145 mm) across cranks of 120–220 mm, and optimal pedalling rate fell from 136 to 110 rpm as cranks lengthened.
16 trained cyclists, cranks of 120, 145, 170, 195 and 220 mm.
Maximum power ranged from 1149 ± 20 W (220 mm) to 1194 ± 21 W (145 mm); 145 and 170 mm produced more than 120 and 220 mm (P < 0.05).
Optimal pedalling rate fell from 136 rpm (120 mm) to 110 rpm (220 mm).
The optimal crank was 20% of leg length or 41% of tibia length, but those ratios explained only 20.5% and 21.1% of the variability in maximum power.
Authors: standard 170 mm cranks should not substantially compromise maximum power in most adults.
Practical Application
Crank length is not a power decision. Across a span five times wider than anything sold for road bikes, sprint power moved by about 4%.
A shorter crank is ridden at a slightly higher cadence for the same foot speed — expect a few more rpm, not fewer watts.
"20% of leg length" is a weak guide: it explains about a fifth of the differences between riders.
Limitations
Short maximal efforts only; sex not stated in the abstract (abstract only was read).