With few stones left unturned in the pursuit of marginal gains at the top of pro road cycling, helmets have seen a lot of development in recent years.
It appears, though, that there’s scope to take things much further than most riders or helmet brands have so far.
We’ve seen increasing numbers of riders wearing the TT-inspired Kask Nirvana and POC Procen Air helmets, while Uno-X Mobility rider Søren Wærenskjold even took victory at the 2025 Omloop Het Nieuwsblad wearing the Tucker MIPS TT helmet.
And with Wout van Aert and his Visma-Lease a Bike teammates wearing Giro’s original Aerohead MIPS time trial helmet at the same race (and in previous events this season), this trend is now firmly in the spotlight.
Could the use of time trial helmets in road races be the WorldTour peloton’s next big source of aero gains?
Let’s examine how TT helmets compare to road helmets, why this hasn’t happened sooner, and what, if anything, the UCI might have to say about it.
How much more aero are TT helmets?
Given dedicated time trial helmets tend to focus purely on aerodynamic performance, with weight and ventilation only minor concerns, they’re generally more efficient than standard aero road helmets.
When former pro Alex Dowsett compared Specialized’s S-Works TT 5 to its Evade 3 aero road helmet at the Silverstone Sports Engineering Hub wind tunnel, for example, he found the aerodynamic difference was 3 per cent.
Using the 44.2km course from the 2022 British National Time Trial Championships as a model, Dowsett says wearing the Evade 3 rather than the TT 5 helmet would have, theoretically, cost him 33 seconds.
Likewise, according to Swiss Side, the difference between a TT and aero road helmet “is superior to 10 watts at 45km/h (more than 5 watts at 35km/h)”.
For context, when we went to the Silverstone wind tunnel in 2023, to test out the best-value aero upgrades, we found upgrading from a set of basic alloy wheels to a set of carbon deep-section hoops saved around 10 watts at 35kph.
At the even higher speeds often seen in the modern peloton, the wattage differences will be magnified further (because the power required to overcome drag increases at the cube of velocity).
What about hybrid TT/road helmets?
An emerging trend from last year was for hybrid TT/road helmets.
Most prominently, we saw POC launch its Procen Air – which is essentially a slightly less aggressive version of its dedicated TT helmet, the Procen TT.
Kask also launched its Nirvana aero road helmet, which features a teardrop shape, minimal venting and subtle ear covers to help reduce turbulence in that area.
According to POC, the Procen Air offers significant gains – anywhere from 5 to 18 watts, depending on the speed – compared to its vented road helmet, the Ventral.
Likewise, Kask says the Nirvana is 4.4 watts more efficient than its Utopia Y aero helmet at 45kph and 10.4 watts more efficient at 60kph.
Clearly, the gains from wearing a proper TT or hybrid TT/road helmet are potentially significant.
Those numbers far outstrip what you’d gain from upgrading to a ceramic bottom bracket, waxing your chain or using oversized chainrings, for example.
So, when riders and teams routinely go to great lengths in pursuit of tiny efficiency gains, it’s notable that TT helmets have – until now – not broken into road racing in the same way skinsuits, extreme head tubes, deep-section rims and other TT-inspired kit have.
What does the UCI say about TT helmets in road races?
The technical rules surrounding helmets are surprisingly relaxed.
Article 1.3.031 of the sport’s technical regulations states basic elements such as a helmet must be “approved in compliance with an official security standard” and have not “been altered or had any element added or removed in terms of design or form”.
Beyond that, though, the only restrictions placed on shape are dimensional.
Provided it fits within a 450x300x210mm box, a helmet can be any shape you like – hence why extreme designs such as the POC Tempor and Giro Aerohead II are permitted.
Given this, riders are free to wear whatever helmet they like for both road races and time trials.
In theory, there’s nothing in the rules to stop Remco Evenepoel taking to the start line wearing a Specialized TT 5 time trial helmet instead of his usual Evade 3, for example. It’s simply a matter of choice.
Jonas Vingegaard could even line up for the start of the Tour de France wearing the Aerohead II if he so desired.
Is the UCI about to clamp down on big helmets?
The only thing worth noting is that, as of 1 February 2025, the following rule – Article 1.3.032 – has been amended to specifically mention helmets regarding items of clothing that change “the morphology of the rider”.
Specifically, the rule now states, “Clothing and other items or accessories worn by a rider (including but not limited to helmets, glasses, shoes or in-race communication devices) may not modify the morphology of the rider.
“Moreover, any non-essential element which is added on (or under) or integrated in any clothing, or other item or accessory worn by a rider shall be forbidden.”
How the UCI will apply this updated rule remains to be seen, though.
At first glance, this could have something to do with the trend for aero baselayers or strategically placed race radios.
Or it could be the result of the UCI’s 'in-depth analysis' into the ballooning size and increasingly outlandish shapes of modern time trial helmets.
Yet, while the Giro Aerohead II shocked the cycling world when it was unveiled, it arguably doesn’t “modify the morphology of the rider” any more significantly than ‘traditional’ teardrop-shaped TT helmets such as the Kask Bambino or original Aerohead do – it’s simply a less familiar shape.
If the UCI were to be strict on this point, all helmets – TT-specific or otherwise – should surely have a rounded, head-like shape like the Giro Air Attack.
As is all too often the case, the UCI’s technical regulations leave us with more questions than answers.
Why don’t more riders wear TT helmets for road racing?
If the UCI doesn’t outlaw the use of TT helmets in road races, it begs the question of why more riders don’t wear them.
The most often-cited concerns are that they have poorer ventilation, are much heavier than aero road helmets, are designed for optimum performance in a fixed position and can impede your peripheral vision and hearing.
Some of these things are clearly true – a helmet that has fewer vents and covers more of your head will naturally tend to be stuffier than one that does the opposite, for example. Giro’s Aerohead II also weighs a claimed 450g, compared to 277g for the brand’s Eclipse Spherical aero road helmet.
However, it’s also true that there are plenty of road races, particularly during the early-season Classics, where limited ventilation isn’t an issue (who remembers the snowy 2013 Milan-San Remo, for example?).
Likewise, the potential aero gains on offer would far outweigh an increase in weight of a few hundred grams in most scenarios, and there are TT helmets, such as the original Kask Bambino, that are designed to allow for increased head movement.
There are ways around the peripheral senses issue, too – the ear covers on POC’s Procen Air are made of a soft EVA foam, for example, and only partially cover your ear to prevent the helmet from blocking out too much sound.
The optimal helmet for any rider is also tricky to discern without proper testing. This is because how a helmet interacts with a rider’s body shape and riding position can affect the performance of different models.
So, while TT helmets tend to be more efficient than aero road ones in general, it can’t be assumed to be the case for every rider and helmet combination in the bunch.
Many pro riders will have access to aero testing, though, and would therefore be able to find out which helmets are fastest for them (and vice versa). That’s presumably how van Aert and his teammates have arrived at using the original Aerohead in road races this year, after all.
Are riders simply worried about looking silly?
In the end, though, Dowsett thinks the reason we haven’t seen more riders wearing TT helmets in road races has little to do with heat, weight or their peripheral senses.
The crux of the matter, he says, is that “everyone is all about the marginal gains… until it looks a bit silly”.
Judging from some of the comments we get on articles and videos here at BikeRadar, a number of the sport’s fans agree.
Dowsett notes, though, that riders initially had similar reactions to things such as skinsuits and aero socks, despite both things now being de rigueur in the pro peloton.
As often with these kinds of things, though, once a high-profile rider – such as Wout van Aert in this case – starts to do something, everyone else sits up and takes notice.
If the Belgian superstar were to win a monument classic, such as Paris-Roubaix or the Tour of Flanders, wearing a TT helmet, it’s not difficult to imagine much of the peloton following suit.
