As coach and sports scientist Garth Fox explains, if you’re a time triallist, your number one enemy is aerodynamic drag. It is always present and will always be working against your attempts to go quicker.
Your bike accounts for around 20 percent of the aerodynamic drag that you encounter, the rest is down to your shape and your frontal area – the part that hits the wind.
To a certain extent, Fox says, this means you can buy ‘free speed’. Things like aero bars, aero helmets and tight clothing all contribute to better streamlining. They optimise air displacement and minimise the low pressure area formed in your wake, resulting in less drag.
An aero helmet can be a cost-effective upgrade compared to, say, an aero-tubed frame. And as there’s often little to choose between aero helmets in terms of aerodynamics, it can easily come down to what’s comfortable.
We recently tested a range of aero helmets in the wind tunnel and on the road, and these three models are the top scorers from that test.
How we tested them
Every helmet was tested in two positions – one super-low and aggressive to test how the helmet integrates with the rider, the other more upright to see how the helmet performs on its own. This lets you choose a helmet to suit your position on the bike. The rider and bike were kept constant and several runs were carried out with each helmet.
It's crucially important to note that aero helmets are highly individual in terms of drag reduction, because your body shape and position on the bike will influence the results too. What’s fastest for one rider might be slowest for another, and vice versa. We've included the data (see below) because it will be of interest to many of our readers, but it should be noted that it is representative of our test rider only.
All testing was done at five degrees to better represent real-world conditions. We also tested a normal road helmet for reference. Then we rode and raced in each helmet. Weights are measured figures for our large size test samples.
Top three aero time trial helmets
- Weight: 393g
- £299 / US$499.95
"It performed brilliantly in the wind tunnel and on the road, it feels even lighter than it is and somehow stays cool enough despite the minimal venting."
- Weight: 565g
- £299.99 / US$400
"The striking looking Wasp was super fast in the wind tunnel in both positions. The shallow visor keeps your face cooler and gives a fantastic field of vision, but pulling it forwards to open the useful vents is tricky"
- Weight: 463g
- £179.99 / US$200
"The Javelin performed brilliantly in the wind tunnel for a head-up position, but below average for head-down.The two front vents channel air through the shell effectively to prevent overheating."
We tested a Giro Aeon road helmet for context and calculated the time saved over it by each TT helmet over 40km (25 miles).
The wattage figures given with each helmet are the power required to sustain 30mph for our control bike and rider using that helmet in each stated position. A difference of 10W at this speed equates to one second per kilometre.
CdA stands for coeffecient of drag (Cd) times frontal area (A). A lower number is better.
This data is for our test rider only and should be examined in that context. Your own results will almost certainly be different.
|Helmet||CdA (Head up)||CdA (Head down)||Saving (head up/head down), in watts, compared to Giro Aeon||Time saved in seconds (head up/head down) over 40km (25 miles) at 30mph, compared to Giro Aeon|
|Rudy Wing Project-57||0.279||0.252||23/23||92/92|
|Catlike Chrono WT||0.275||0.248||29/30||116/120|
|Giro Aeon (control)||0.295||0.268|
It's important to note that because air resistance increases to the square of speed, the savings at, say, 20mph are less. It takes 2.25 times the power to sustain 30mph instead of 20, so a difference of 10W at 30mph would be 4.4W at 20mph.
It's standard practice to test at 30mph because lots of aero kit is designed for top level time trialling, where that's a typical speed. It also adds resolution to the data, showing up differences more repeatably than if the testing were carried out at 20mph.
We’ve tested seven of the very best TT helmets on the market, so keep in mind that the performance figures are relatively close. If we included another half dozen, especially older and cheaper designs, then we expect we'd have seen a bigger spread and numbers that would have cast the likes of the LG in a less unfavourable light.
The Kask Bambino is our winner. It’s super fast, versatile and light. Only the small sizing stands in its way.
If you have a big head, the excellent Lazer Wasp offers a bit more room.
And, very simply, if you can afford neither, then buy the very decent Bell Javelin.