Lighter bike won't get you to work faster, says doctor

By Richard Tyler | Wednesday, December 15, 2010 11.30am

A six-month trial into the effect of bicycle weight on commuting times by a British doctor is likely to stoke the eternal 'steel versus carbon' debate after he concluded that the lighter material may offer little to no advantage to the average ride.

The independent, though light-hearted, trial published in the British Medical Journal was carried out by Sheffield-based anaesthesia and intensive care consultant Dr Jeremy Groves.

Between mid-January and mid-July this year, Dr Groves compared the difference between the time taken to cover his daily 27-mile (43.5km) commute on his trusty 29.75lb (13.5kg) steel framed bicycle and a new 20.9lb (9.5kg) carbon bike.

"A 30 percent reduction in bicycle weight didn't reduce commuting time over a distance of 27 miles," concluded Dr Groves, who used the toss of a £1 coin to determine which bike he would ride on a given day during the trial. "A new lightweight bicycle may have many attractions, but if the bicycle is used to commute, a reduction in the weight of the cyclist rather than that of the bicycle may deliver greater benefit and at reduced cost."

Dr Groves had been motivated to discover whether claims that a new bike would knock up to 10 percent off the time taken to complete his daily commute could be proven. He bought a £1,000 carbon-framed road bike via the UK government's Cycle to Work scheme and alternated between it and his £50, second-hand steel bike.

Data used in the study was drawn from 56 journeys (26 on the carbon bike and 30 on the steel bike) and found that his mean journey time was 32 seconds faster on the steel bike. Time was the only form of data used in the study, with power output, the difference in position and componentry (such as tyres) between the two bikes and external factors such as traffic and weather neither measured nor taken into account.

In his assessment of the data collected, Dr Groves pointed out that any reduction in the weight of a bike is far less significant than a reduction in the combined weight of bike plus rider. He acknowledged the limitations of his single-subject trial.

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"Though a 30 percent reduction in bicycle weight may seem large, the reduction in total weight (bicycle and rider) of four percent is much less impressive," he said. "The effect this weight reduction has on the forces acting against the cyclist (gravity, rolling resistance, wind resistance and the force to accelerate bicycle and rider), as well as the effect of the road conditions, need to be considered."

"Acceleration is a little more complex... particularly with respect to wheels, where lighter rims can confer a significant advantage, but only if there are a significant number of points of speed change on the journey. There weren't enough on mine."

Dr Groves stopped short of recommending that riders opt for heaver or cheaper models of bike over their lighter counterparts, noting the indeterminable psychological effect of a given machine. "The purchase of the carbon bike made me feel good and even though the ride is 'harsher', I still commute on it, especially in good weather," he said. "I haven’t compared the brakes but they seem better.

"Which do I enjoy riding most? Well, after the trial I have to go for the steel bike. I get there as quickly and it's more comfortable, better value and has more 'character'. If the carbon bike were stolen would I replace it? I’d have to say no. I’d spend the money on high-visibility, low-drag clothing and better lights."

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