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Does shaving your legs make you faster?

Rupert Paul
22 Mar 2019

Shaved legs obviously slip through the air better than hairy ones. Or do they?

Does shaving your legs improve your performance on the bike? At first, the answer seems obvious. After all, look at a picture of Sir Chris Hoy. His magnificent, brawny legs – the ones that won him five gold medals – are shaved. Argument over. After all, the GB Olympic team are famed for having turned the science of marginal gains into precious metal.

The only snag is, Sir Chris may not have been shaving his legs for aero effect. Riders give many reasons for hair removal – cuts are easier to keep clean, it chafes less.

Equally important, shaved legs might simply make you look and feel faster. They certainly mark you out as a cyclist. Or at least they did. Now there’s a theory that hairy legs might somehow create less drag than smooth ones, however bad they might look on a summer's day in the saddle.

Built for speed

This sounds weird. In nature, fast creatures are almost always sleek. A yellowfin tuna (45mph) is a pretty spectacular low-drag specimen, with skin smoother than an aircraft and stiff, sharp fins that fold back into slots for high speed sprints.

Dolphins (up to 33mph) show a similar attention to detail. ‘Their bodies are covered in specialised skin,’ says Dr Lissa Batey, marine biologist with The Wildlife Trusts.

‘The blubber layer ensures the skin’s surface is streamlined. The outer layer also improves hydrodynamics by continually exuding oil droplets and shedding epithelial cells.

‘The shedding of cells improves laminar flow by interrupting the formation of vortices and the oil helps to lubricate the skin, allowing the water to pass over it more smoothly.’

But cyclists are not dolphins, and as land creatures we have to go about chasing low drag rather differently.

Mike Burrows, the aerodynamics expert who designed Chris Boardman’s Lotus 108 carbon TT bike, explains why: ‘If something’s a very nice shape, then you want the surface as smooth as possible to achieve laminar flow.

'If something’s not a very nice shape – ie your leg – you don’t want a smooth surface.’

A rough guide

Burrows cites a famous wind-tunnel experiment in the 1930s which looked at the wake coming off the back of a simple sphere.

‘It was twice the size of the sphere. But then they put a thin piece of wire around the sphere just before the widest point. It halved the diameter of the wake.’

So could leg hairs be there for this reason, as a kind of low-drag evolutionary adaptation? Are there, in fact, any other examples of fast, hairy things? Well, there’s always tennis balls.

‘The hairs on a tennis ball can give it lift,’ says Derek Price, managing director at Price Of Bath, Europe’s only ball manufacturer.

‘It depends how clever the tennis player is – whether it’s top spin, bottom spin or side spin. But for a ball just fired straight, left to its own devices, the hairs’ effect is to slow it down a bit.’

So far, so inconclusive. Perhaps Rob Dean can help. Not only is he a Santa Cruz-sponsored endurance MTB racer, he’s also a mechanical engineer at General Electric (GE).

‘I shave my legs for keeping cuts clean more than anything else. There’s also a comfort issue; dried mud can be like a ball bearing waggling around on every single leg hair – extremely uncomfortable and distracting.’

Aero gains?

OK, but what about the aero theory? ‘As an engineer I’m not convinced about the aero benefits of shaved legs.

‘While it helps cut through the air at the front, hair will also promote a turbulent boundary layer behind, which helps the air stick to the surface and reduces drag.

‘Ideally one might shave the front of the leg and leave the rear hairy. This use of a rough feature is actually legislated by the UCI in time-trial suits.

But these are extreme solutions. I can’t imagine anyone apart from time-triallists using this. I’ve thought about it, though!’

Citing the wind-tunnel experiment with the sphere and wire, Burrows takes the partial shaving theory a stage further. ‘All you need is a little turbulator strip. So the joke is you give yourself a double Mohican on your legs just before the widest part.

‘It’s very difficult to do, and it would look very silly. But I rather suspect British Cycling did this with their skinsuits. Certainly for Beijing they were talking about it – little turbulator strips sewn into the suits to trip the air up just before it got to flow round your arms and shoulders.

‘Potentially it has an enormous advantage, though you need to do wind-tunnelling to optimise it.’

The body of evidence

One man with access to a wind-tunnel is Simon Smart, technical director of Smart Aero Technology. A former F1 engineer, Smart is the UK leader in aero technology and riding position optimisation. So he knows whether leg hair – or the absence of same – matters. And it doesn’t.

‘Your body can contribute as much as 85% to the drag of the rider/bike system, so getting the right body position, without compromising power and comfort, is the most important element,’ he says.

‘Unfortunately there are no hard and fast rules – air flow works differently with varying body shapes and positions.’

Smart’s wind-tunnel tests show that a good adjustable set of aero bars is far more useful than a tube of Veet. After that it’s helmet (the best option varies from rider to rider) and skinsuit.

‘The difference between a good and a poor skinsuit could be as much as 25 watts. That equates to 2.5 seconds over 1km, which is significant in a 25-mile time-trial.’ In the world of wind-tunnel-tested performance gains, leg hair doesn’t get a look in.

Do it yourself

No one has yet wind-tunnel-tested the double Mohican strip or the half-shaved leg, but Burrows suggests a variation we can all try: ‘A 3mm strip of insulating tape down either side of the down tube, about a quarter of an inch in front of the widest part. You’re not going to get two minutes out of it – but it doesn’t cost anything and you might as well do it.

‘But shaving or not? It’s very theoretical. In the real world it probably doesn’t matter one way or the other.’

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