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Is weight better on the bike or on your back?

weight on bike
James Witts
13 Aug 2015

Professional cyclists have been known to move their bottles into their pockets to climb faster. But does it really save energy?

In The Rider, author Tim Krabbé recounts a story about the lengths Jacques Anquetil went to in search of victory: ‘He used to take his water bottle out of its holder before every climb and stick it in the back pocket of his jersey. Ab Geldermans, his Dutch lieutenant, watched him do that for years, until finally he couldn’t stand it any more and asked him why. And Anquetil explained.

‘“A rider,” said Anquetil, “is made up of two parts, a person and a bike. The bike, of course, is the instrument the person uses to go faster, but its weight also slows him down. That really counts when the going gets tough, and in climbing the thing is to make sure the bike is as light as possible. A good way to do that is to take the bidon out of its holder.” So, at the start of every climb, Anquetil moved his water bottle from its holder to his back pocket.’

Doubt has been cast about the veracity of the story, not least because of the lack of photos of Anquetil with bottle in jersey, but in these days of marginal gains, we wanted to find out if the Anquetil approach would offer any advantage. 

The pendulum swings

‘I don’t think there’s been any published literature on this topic, so the closest analogy is backpacks and load carriages,’ says Stephen Cheung, professor in environmental ergonomics at Brock University in Canada. ‘Intuitively, I’d have said the lower the weight placement, the lower the metabolic cost because a lower centre of gravity requires less energy simply to remain stable. However much of the backpack research doesn’t reflect this.’

A study led by Professor Abe of Kyushu University in Japan looked at the energy cost of walking with loads that corresponded to 15% of the subjects’ body mass. Fourteen subjects walked on a treadmill in five-minute increments with and without loads on their back, and the results showed that energy cost was reduced when they carried the load on their upper back compared to their lower back.

‘The theory is that the load at relatively low speeds acts as a rotating pendulum, decreasing the amount of energy costs [by returning energy back into walking motion],’ says Cheung. ‘However, at the greater speeds of cycling, I don’t think this pendulum effect would be an aid.’

Indeed, the lateral movement of the bottle in the pocket could inhibit economy if the bottle is not held firmly, according to Andy Ruina, professor of mechanics at Cornell University in America. ‘It’s all down to energetics and power,’ he says, before calculating how much power might be wasted by Anquetil’s water bottle slipping ever so slightly in his rear pocket. ‘In this case, power is force multiplied by distance moved by the bottle multiplied by the number of times it slips each second.

‘Let’s say Anquetil’s metal bottle and liquid weighs 1kg, it slips back and forth 1cm each time he pedals, and his cadence is 90rpm so it slips three times each second,’ Ruina adds. ‘Taking that equation, you have force [gravity x mass], which is 9.8 x 1kg x 0.01m of sliding multiplied by three strokes per minute. That equals 0.3 watts wasted from the bottle moving about in the rear pocket.’

Keep still, dammit

weight on back

So that’s it. When ascending, Anquetil was wrong to place his bidon in his jersey pocket. Not quite, says Cheung. ‘When you climb out of the saddle, your upper body should remain relatively stable and so have less lateral movement than the bike, which you’re swinging from side to side. So by putting the bottle in his shirt, his bike will not only feel lighter, there will be less energy lost from the side-to-side motion of his bike.’

‘No, I don’t agree,’ says world-renowned bicycle technician, framebuilder and tech writer Lennard Zinn. ‘If you’re out of the saddle, you’re constantly lifting your body up and down with the pedal stroke, even if your upper body isn’t moving laterally too much. So even though you’re moving the frame more, I’d still argue that the lower the weight of the bottle is held, the less energy is wasted.’ It’s a theory supported by professional WorldTour teams, who often add extra weight to their bottom brackets to hit the UCI minimum weight regulations of 6.8kg, although they don’t have the choice of carrying ballast in pockets.

Ruina, Zinn and Cheung all agree on one thing, however: if your bike’s on the flat and remains upright, the energy cost of having the bottle held in the cage or in your jersey pocket would be the same because you’re not moving up and down as you might be when sprinting or climbing. 

‘Then again,’ muses Zinn, ‘things change if Anquetil had a water bottle on his handlebars.’ Until the 1960s, cyclists often carried a second bottle on the handlebars because, at the time, Tour rules stated that riders must carry a pump, which often took up the entire length of one frame tube, leaving no room for that second bottle cage.

‘I can see the benefit of putting a bottle in your pocket if you had been carrying it on the handlebars,’ Zinn adds. ‘Your bike would really snake around in front of you if you’re exerting yourself like up a hill or in a sprint, and you’d haemorrhage energy just trying to remain in a straight line.’

The concept of sprung and unsprung weight has so far remained outside of this discussion, but comes into play when speeds pick up, according to Zinn. ‘On a descent, and if the road is quite rough – which is more likely on a mountain bike – the weight of the bottle is better off on your back, because of the extra suspension afforded by you, the rider,’ he says. A bottle held tightly in the frame by contrast would be forced to move with every bump in the road, costing energy. ‘And then there’s the issue of when the bottle isn’t full. You’ll lose energy through friction of all that sloshing,’ Zinn says.

So it seems the science on this subject, like the original story about Anquetil that inspired it, is inconclusive. But if it gives you a psychological edge, it might be worth a try…

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