Cyclist

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

- Words PADDY MADDISON Photograph­y ROB MILTON

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.

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