Heart rate versus effective road speed for different crank lengths. Cadence was adjusted to suit each crank length: ie at 15mph, 175mm were spun at at 79rpm, 125mm and 100mm at 89rpm. Peak power of 780 watts was recorded with 175mm cranks, but both 155mm and 125mm managed 770 watts, and 110mm, 705 watts.

I too used to belief firmly that 150mm cranks were only for kids, or adults with very short legs. In fact, after much experimentation, I came to the conclusion that extra-long 185mm cranks suited me best, and that the formula put forward by Kirby Palm [see www.nettally.com/palmk/crankset.html] was correct.

Then two of my customers, Rob Hague, and Mark Mueller started experimenting with short cranks. Rob found an improvement in his race times by going from 170mm to 150mm, even though he has long legs! Mark found that after training for a month with 110mm cranks, he was back to the same performance he was getting with 170mm cranks. My son Paul tried 100mm cranks on his trike and found so much improvement over normal length cranks, that there was no way he was ever going back to normal ones.

Then a customer, Irene, who had hired a trike with 165mm cranks for three months, came to take delivery of her new trike. I measured her legs against the formula, and discovered that according to Palm, she needed 150mm, so I fitted a pair of 150s for her.

After a few days I got rave emails from her saying how smooth the trike felt, and how much better than the demo it was.This seemed rather puzzling to me, as the hire trike was a little lighter.Then she told me that with the new trike, she did not get leg cramps any more, which had been a problem for her with the old trike.Then the penny dropped. It was the cranks which had made the difference.

Next, Paul built a trike to race at the 24hr Pedal Prix at Wonthaggi.Without time to train all the team on 100mm cranks it was decided to use 150mm cranks. Despite losing a few laps following the collapse of an experiment wheel which had been fitted by mistake, they won the race by three laps! Paul then did some tests on our new Computrainer machine and came up with the following results. In all it seems than the higher cadence gained by using short cranks, has no negative effect on power output, and gives an improved leg function, with reduced stress.

On a recumbent, short cranks also help to get a 69rpm, 155mm more efficient aerodynamic were spun at fairing over the rider’s legs.