Head of speed
They are the latest weapons in the arms race for ‘free speed,’ but what real advantages do aerodynamic road helmets offer, and will they ever gain acceptance outside the pro peloton?
The scene was set for an uninteresting 173km of flat riding on Stage 13 of this year’s Tour de France. But in heavy crosswinds the unpredictable nature of the Tour came to the fore when Contador and Team Saxo-Bank broke away from the pack with an impromptu team time-trial into Saint-Armand-Montrod to pull back 57 seconds from Froome’s lead. Team Saxo and eventual stage-winner Cavendish were all wearing the latest in aerodynamic headwear, and if the hype is to be believed, it was the perfect example of how small improvements in aero technology can contribute to time gains.
Aerodynamic road helmets are not entirely a new thing. While bunch riding tends to negate a lot of aerodynamic gains, tales of riders covering their vents with clingfilm for a marginal benefit in a sprint or breakaway extend back into the annals of cycling history. In recent times the trend of using plastic covers over conventional road helmets has been commonplace, and subsequently banned by the UCI. Mark Cavendish’s 2011 World Championships win was perhaps the most public display of such antics, where he used a clear plastic cover over a Specialized Prevail to gain the edge in the final sprint.
After a crackdown by the UCI, manufacturers responded by developing normal road helmets with plastic covers integrated into the design (or maybe simply glued on) to get around the rules. However, this approach was only ever a temporary fix for most brands, and pretty soon the race was on to create the most efficient aerodynamic helmet suitable for the demands of true road riding. The question is, is this marketing trickery at its worst or will the future of road riding be crowned by aerodynamic lids?
Let’s go back to where it all began…
The 1980s saw a whole array of attempts to streamline the head. It began with British pro Dave Lloyd’s ‘skinhat’ in 1983, basically a glorified balaclava. The idea wasn’t a keeper, but only a year later American rider Steve Hegg was sporting a teardrop helmet at the Los Angeles Olympics that could be argued to be the first legitimately aero shell, in the same vein as what we see in pro TTs today.
Indeed, the development of the aero helmet pre-dates many of the more conventionally observed aero adornments – tri bars, aero tube shapes and so on. The reason, quite possibly, is that aerodynamic losses at the head are more significant than you might think.
Chris Yu, an aerodynamics engineer with Specialized, explains why. ‘If you’re sitting in the pack, the frame and the wheels will get a better draft, whereas the helmet is higher up, closer to the whole airstream speed,’ Yu says. ‘The other reason is that the head is a very poor aerodynamic shape; it’s basically like a sphere and that shape is very inefficient, aerodynamically speaking.’
So the appeal of an aero helmet is obvious. However, Dr John Hart, an aerodynamicist from Sheffield University paints a slightly more complex picture. ‘The head can be aerodynamically inefficient but this depends on your cycling style and position. Helmets have a disadvantage straight off in that they add frontal area to a cyclist, a key factor you want to reduce if you are trying to minimise drag.’ The helmet’s size (being necessarily bigger than the head) and position (prominent in the air flow) are therefore natural obstacles when it comes to improving aerodynamics.
Then there’s the problem of vents. ‘Vents will generally mean the drag force of a helmet goes up,’ Hart says. Hence Cavendish’s vent-covering tactics at the World Champs. Many brands have been happy to produce an aerodynamic cover for vents but, Hart points out, ‘You can reduce the impact of vents on overall drag by how you position them and clever design,’
In short, the head is an aerodynamicist’s nemesis, and different manufacturers have taken very different approaches in their attempts to improve the situation.
The rise of the aero helmet
One of the first brands to really rethink ventilation, shape and all things aero
was Giro, which released the first truly dedicated aerodynamic road helmet this year, the Air Attack. Giro’s Rob Wesson explains, ‘The industry is going that way [towards aero components]. We saw that riders and manufacturers were paying a lot of attention to aero so we started thinking, “How can we produce a helmet to do the same thing?”’
The Air Attack was launched around the same time as a range of similarly pitched helmets from other manufacturers, but many were primarily fixed aero covers that circumvent the UCI’s strict rules on helmet attachments. Lazer’s Helium FAST is one such example. Tim Cornelius from Lazer explains, ‘The inspiration for the Helium FAST comes from our aeroshell – a removeable cover. It was used in the Tour Down Under in 2012, and in 2013 we tried to use it again but it was banned by the UCI. So the UCI now states that if you have a shell it needs to be fixed on the helmet. That’s why we created the Helium FAST.’
Permanently fixing the cover on the helmet may seem like a basic solution, but Scott’s helmet product manager, John Thompson, explains that it’s not that easy. ‘We built an aeroshell over our conventional road helmet, but it’s not a simple cover,’ he says. ‘What we have is a shell that is bigger and bulkier than the helmet you normally have, but with an aerodynamically ideal shape.’
As for why some manufacturers are shying away from completely new aero helmets in favour of modifying their existing models, he explains, ‘It’s linked to how helmets are manufactured. Certification is an expensive process and we have a helmet right now for the team that conforms and is certified by simply adding a cover. I wasn’t happy to go through a process of making a slightly modified aero helmet without properly doing the research – I want to make a proper helmet from the ground up.’ With that in mind, it’s likely that the type of covered helmets now seen at pro level are an interim stage in development, with more ground-up designs likely in the future.
Covering vents with a shell is certainly one solution to the aero puzzle, but it comes with its own problems. Hart explains, ‘Having no vents will always be best, but how do you then cool your head? It becomes a trade-off between acceptable cooling and acceptable drag performance.’
Madison Genesis pro rider Liam Holohan draws on his own experiences in support of that. ‘Andy Tennant and I both used the Air Attack in the opening stage of the Tour of Taiwan,’ he says. ‘The day was super-hot, around 38°C, and we kind of regretted it. But everyone else was hot too, so it’s hard to say if using them made a difference.’
While the British climate wouldn’t usually punish a rider for using a ventless aero helmet, it’s clear that very hot riding and hill-climbing could present a problem with lack of ventilation. However, a more sophisticated approach to design could make vents more viable, aerodynamically speaking.
Thompson explains the early work Scott has done on designing for improved airflow. ‘We do as much wind-tunnel testing as possible in as many positions as possible. We use the wind-tunnel as much for ventilation analysis as aerodynamics, and that’s how we ended up bringing our Split TT helmet to market with so few vents.’
Helmet airflow involves a balance between adequate ventilation and aerodynamics. Thompson says, ‘We found on some standard road helmets you actually have a low pressure area causing air to flow into the back vents if you don’t design your airflow and your internal channels correctly. That’s completely counterintuitive and creates more drag.’
Specialized has covered a lot of ground in pursuit of airflow design, according to Yu. ‘We spent a lot of time on ventilation on the Evade,’ he says. ‘And the majority of the design time was figuring out how to achieve good ventilation, but from an aero drag standpoint.’ Not all vents are necessarily counterproductive, Yu argues. ‘Actually in the Evade project we found that the gill vent on the side, which was primarily a ventilation feature, also made the helmet faster too.’
In the case of the Evade, Yu argues that frontal vents do not hinder speed. ‘We found that vents on the front didn’t really hurt aero performance at all,’ he says. ‘The reason is that as air comes to a stop it needs to stop anyway – whether that’s on the surface of the helmet or on your head. And then if you make other vents longitudinal along the length of the helmet then the airflow has a better chance of flowing back off the surface – creating better aerodynamic results.’
Other helmets attempt to solve the ventilation problem using similar air-diverting trickery, such as Kask’s Vertigo Tri or Garneau’s Course helmet, which have various vents but attempt to create a more aerodynamic flow through them. Dr Hart from Sheffield University mentions the difficulties of designing vents with a view to creating better flow. ‘You can take a less streamlined object and delay the separation [the point at which smooth airflow stops] to improve its performance,’ he says. ‘This generally works by “tripping” the flow over the object to prevent separation. You can do this with a surface pattern (think golf dimples), a roughness (fine sand paper), or physical trip features, such as turbulators, or it could be a lip edge. Such techniques, however, have to be used with caution. If you get the position or shape wrong you can make things worse.’
Vents or no vents, it’s worth stepping back and asking the question of whether the gains to be made are significant enough to really make a difference to road riding.
The exact power savings to be made from any one component, including helmets, is a tricky area to discuss, as you quickly find yourself launched into the manufacturers’ world of stats.
Both Lazer and Giro generate similar statistics in support of their aerodynamic, but largely ventless, designs. ‘The Helium FAST offers savings of between 4 and 10 watts when cycling at 45kmh, or more easily put, it saves between 12 and 40 seconds over a 40km ride,’ Cornelius says. Giro is slightly more modest on its claims for the Air Attack. Over a 90km TT, Giro estimates, the aero helmet saves 41 seconds over its top standard helmet, the Aeon.
Specialized’s claims fall between the two. Yu says, ‘We’ve measured many riders, and the wattage difference at 40kmh was roughly 10 watts improvement for the Evade over the [non-aero] Prevail. That jumps up exponentially to nearly 20 watts if you’re going 50kmh,’.
When you consider that Specialized itself claims a 22 watt gain at similar speeds for the Venge, its top aero road frame, it’s clear that a helmet could make a significant difference. But is it as simple as that?
Hart explains, ‘Your helmet choice can affect the flow over your shoulders and back, but that’s dependent on your riding position.’ Wearing an aero helmet but riding in the wrong position can actually make you less aerodynamic. That’s one of the reasons why long-tailed TT helmets are falling out of fashion,
as riders who look down will actually become less aerodynamic as a result of the protruding tail.
Holohan supports this. ‘Your main concern is body position, it causes so much of your drag, way more than the bike or the helmet. If I was going to spend money anywhere on the bike it would be on adapting my position.’
With the potential gains to be made (with correct position, of course) it’s
no wonder aero helmets are popular amongst pros. We spoke to Richard Handley, pro rider with Rapha Condor-Sharp, who races using Kask’s Vertigo Tri.
‘I remember at the World Championships they were claiming something like an 8 watt advantage for a filled-in helmet compared to a regular helmet, so it’s not something to turn your nose up at.’ Handley says. ‘That’s a year’s worth of training to get a similar improvement for some riders. But I think these things aren’t really noticeable or measurable on their own; it’s only when you combine all these things on race day that all the little percentages add up.’
As for riders who aren’t involved in 70kmh sprints, the benefit may be a little less apparent. A general rule of aerodynamics is that gains are progressively more pronounced at higher speeds, so for those of us who ride at a more stately pace, are the gains going to outweigh any sacrifices, or the cost?
If Yu is to be believed, yes they will. ‘Although the wattage savings are smaller, if you’re going at lower speeds in a sportive then you’re taking longer to finish, so you actually end up saving more time than someone travelling faster,’ he says.
Some might be tempted to question that statement, but aerodynamicist Hart seems to concur: ‘You can do a couple of simple calculations to show that you get the same savings if you assume drag coefficient is constant regardless of speed, and if you neglect all other forces,’ he says. ‘In that instance both fast and slow riders get the same “percentage” time saving.’
So, the final question: are aero helmets here to stay and will they perhaps even come to outnumber conventional road helmets? Considering that the helmet may render better aero gains than a top-of-the-line aero bike frame, at a fraction of the cost, they may well do. As Hart says, ‘Let’s put it this way,
the choice of your helmet can lead to significant drag savings. It’s also the easiest thing to change shape-wise to get some dramatic gains without it necessarily affecting or being affected by anything else.’
There’s still one drawback though, which is spelled out by Holohan when we ask whether he trains with his aero helmet. He says, ‘I don’t wear it while training, no,’ Why? ‘Because I’m vain.’