Question: I’m a 36 and a competitive triathlete, usually placing top-5 in my age group. I use 170-mm crankarms but have heard that for time trialing, longer is better. Is that true? — Harold F.
Coach Fred Matheny Replies: There have been studies of crankarm length, but the results aren’t consistent. Some show that longer cranks provide greater leverage for turning big gears. Some show that shorter cranks foster greater speed via a faster cadence. And some show that crank length is completely individual.
So, longer crankarms aren’t a panacea for time trialing. In fact, there are dangers associated with them. The added length makes your knees bend more at the top of pedal strokes and extend more at the bottom — both of which can lead to biomechanical injuries if you jump from 170 mm to, say, 180 mm.
Also, longer cranks reduce cadence — and a brisk cadence is the key to good time trialing.
All this said, most time trialists use crankarms about 2.5 mm longer than those on their normal road bike. Because 2.5 mm (one-tenth of an inch) isn’t much, it rarely causes an injury. But the jury is still out on whether that bit of extra length actually improves performance.