More power to pedal pushers?

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Revolutionary crank could speed cycling.

The sun wheel (left) varies the pedal-to-chain wheel distance

A peculiar pedal-crank from Italy, the spiritual home of cycle racing, may make future bikes faster. A cyclist could go a kilometre further in an hour with the new pedal, researchers estimate1.

Bicycle handlebars have got bendier, their frames lighter and their wheels narrower, but there have been few lasting improvements to the basic design since the invention of the safety bicycle in 1890.

Then retired car mechanic Antonio Batistuta sent a prototype of the unorthodox pedal to Paola Zamparo, a biomechanical engineer at the University of Udine in Italy, for testing.

"It's funny-looking but it seems to work," says Zamparo. The breathing rate of volunteers on fixed bicycles showed that, at high speeds at least, the prototype is about 2% more efficient than a standard design.

The new pedal revolves around a 'sun-wheel', rather than a fixed point, at the end of the crank arm that connects the pedal to the wheel driving the chain. The sun-wheel varies the pedal's position in relation to the crank's pivot-point, effectively lengthening and shortening the crank arm.

Lengthening the crank arm increases the leverage available to the cyclist on the downward power-stroke. On the upstroke, which generates little or no power, a shorter crank arm reduces the amount of energy needed to return the pedal to its original position.

"It's odd that [the prototype] works," says Zamparo. Previous efforts to exploit this principle have been tried. As early as 1820, before bikes even had rubber tyres, inventors experimented with elliptical and off-set chain wheels that had the same effect as a variable crank arm. But these modifications never passed muster.

"It's interesting and potentially useful," says Steve Kautz, who studies biomechanics at the University of Florida in Gainsville. "However, if it works, I don't believe it is for the same reasons that they suggest." He suspects the pedal may help the cyclist transfer slightly more power to the bike from their legs' muscles and bones.

“>There's no way to play around with the mechanism and get much more power Edmund Burke , University of Colorado”

Edmund Burke, a sports scientist at the University of Colorado in Colorado Springs and author of High-Tech Cycling, agrees. "There's no way to play around with the mechanism and get much more power," he says. "It must be due to more subtle effects."

A commercial version of the pedal would have to be more compact and lightweight, says Zamparo. Even if Batistuta's patented design catches on, it might not be powering the Italian cycle team to victory in the next Tour de France.

The Swiss-based Union Cycliste Internationale, which regulates the use of new technologies in bicycle races to keep them fair, could frown on the newfangled design. "They can be very fickle," says Burke.

References

  1. 1

    Zamparo, P., Minetti, A. E & di Prampero, P. E. Mechanical efficiency of cycling with a new developed pedal-crank. Journal of Biomechanics, 35, 1387 - 1398, (2002).

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Clarke, T. More power to pedal pushers?. Nature (2002) doi:10.1038/news020923-12

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