Building a head of speed
An aero helmet saves watts, but who wants a bowling ball on their head? The latest designs aim to find a sweet spot between speed, weight and style
Aerodynamic helmets are nothing new, but it’s only in the past decade that they’ve become a realistic option for the everyday cyclist. Prior to Mark Cavendish riding to victory in the 2011 World Championships with a plastic cover on his S-works Prevail, the only truly ‘aero’ helmets were those worn by time-triallists.
For the rest of us, their silly looks and general unwieldiness far outweighed any potential performance gains.
Fast-forward to today and aero-optimised lids make up a sizeable segment of the road helmet market. Every major manufacturer now offers at least one aero road option alongside its traditional vented helmets. But what are the benefits, and is it worth making the switch if you’re not Mark Cavendish? ‘A well-designed aero road helmet will provide a measurable reduction in aerodynamic drag when compared to a normal helmet,’ says Ben Penner, director of product development at Giro. ‘That said, this gap is narrowing as lessons we’ve learned with modern aero road helmets trickle down to regular road helmets.’
To give an idea of what level of drag reduction can be expected, Giro claims its smooth, aero-optimised Air Attack helmet is 17 seconds faster over 40km than its Aeon model, which has 24 vents. It may not sound like much, but that sort of marginal gain could be race-winning stuff.
‘The Air Attack was largely designed to give sprinters an edge at very fast speeds and arguably defined the modern aero road helmet category,’ says Penner. ‘Aesthetically it was very controversial, but its performance gains were undeniable, and we saw all our top competitors rush to imitate the design.’
Other brands make similar claims. Specialized, for example, compared its Prevail road helmet and Evade aero road helmet at its ‘Win Tunnel’ testing facility in California, and found opting for the latter could save 46 seconds over 40km compared to the former.
Search for speed
Aero road helmets achieve this reduction in drag in a number of ways – it’s not simply a matter of fewer vents equalling greater speed.
‘You might assume that removing vents produces automatic gains, but that’s not always the case,’ Penner says. ‘It’s possible to have a vented helmet that’s faster than one with no vents if the vented helmet has an aerodynamically superior shape.’
‘The shape is tuned to let the air flow as closely as possible to the surface,’ adds Matteo Tenni, project manager at Met and the man responsible for running the brand’s engineering and design team. ‘This minimises turbulence and reduces drag.’
There are two key factors that affect drag in helmet design. The first is the drag coefficient, which is a measurement of how effective a given shape is in reducing air resistance
– this is where vents and overall helmet shape come into play. The second is the
‘The shape is tuned to let the air flow as closely as possible to the surface. This minimises turbulence and reduces drag’
area of the helmet that meets the wind (the front). The more compact the area, the more efficiently the helmet will cut through the air. ‘We try to optimise both,’ says Penner.
Yet like most advancements in cycling tech, aero road helmets aren’t without their snags. The biggest drawback becomes glaringly (and sweatily) apparent as soon as you attempt a long climb with one strapped to your head.
‘Aero helmets typically have fewer vents, or at least slightly smaller vents, than normal helmets,’ says Tenni. ‘For these reasons, climbing a hard slope at a high temperature and a slow speed is probably not the best application.’
It’s a point echoed by Giro’s Penner: ‘Historically the most obvious drawback has been decreased ventilation, and often there’s a weight penalty due to increased materials. But as you look at the progression of our designs, you see improvements in both areas while still managing to make aerodynamic gains.’
Where can we expect aero road helmets to go from here? At Met, Tenni says the future of aero road helmet development lies in new ways of testing. ‘We aim to optimise aero performance through virtual modelling and numerical simulation. This allows us to tweak details and optimise the shape without having the physical helmet on hand. Then it’s all about optimising performance during an impact. After all, that’s the main reason for which the product is designed.’
But the problem with designing anything to be aerodynamic is that there’s only so far you can go. Once something is as aero as it can possibly be, how do you make it any more efficient? For Penner, it’s a question of overcoming the drawbacks.
‘As designs become more aero, it becomes increasingly difficult to pull out further aero gains. That’s why our current research and design is focussed on creating helmets that almost eliminate any performance or protection disadvantages. That way, riders aren’t forced to choose between aero versus ventilation or weight.’ If helmet manufacturers achieve their goals, we can expect a future where we don’t have to choose the helmet that best suits our needs – there will just be one that does it all.