Ask most athletes how to choose a time-trial helmet and the answer comes back in three words: buy the fastest.
It is an understandable instinct and a poor method. For Ironman racing, and indeed for UCI time trial, the right helmet is not a shape you pick off a shelf. It is a system decision — one that depends on your position, the discipline, the terrain, the heat, and, at the very finest end, the surfaces around it. Get that decision wrong and a genuinely fast helmet can quietly cost you the race.
For this piece, we put the helmet question to Ken, the founder and owner of Sync. His answers are woven in throughout.
Position Comes First
A helmet’s aerodynamic shape only means something in the head position it was designed and tested for. Manufacturers develop and tunnel-test their helmets at a particular head angle, with the rider holding a particular posture. Hold a different posture, and the shape stops doing what the brochure promised. This is why position has to be the first decision, not the last.
Helmet selection is very sensitive to head position, meaning it is hard to select the best helmet until you know what the realistic head position is — both the proximity to your forearms [the vertical helmet position] and the tilt of your head. These are massively variable and obviously quite situational.
That realistic head position is a moving target. The athlete new to a TT position rides with their head higher, looks up the road more frequently, and tilts their chin more aggressively up when they do. As confidence grows, head carriage drops, the lifts get less severe, and the lower position holds for more of the ride. As an athlete’s understanding of aerodynamics sharpens — what head position actually costs — the same pattern accelerates.
Because helmet choice is so sensitive to head position and overall posture on the bike, evaluating the best option needs to be considered the moment a position changes, or an athlete gains confidence in their ability to maintain a more optimal head position. Having your TT position optimised is more critical and a first step, before going to town on the helmet options.
For triathletes specifically, the realistic position is rarely the absolute lowest position. Draft-zone compliance generally means looking 20 metres up the road, which keeps head carriage a touch higher than a pure ITT effort would. In triathlon, athletes also don't have follow cars and radios, critical safety considerations. That is not a problem to be solved — it is the reality that the helmet has to suit. None of this diminishes the value of a good helmet for triathlon. It simply sets the context for what “good” means in practice.
This is why we steer clear of universal claims about how much any helmet saves. The honest answer is that it depends entirely on the rider underneath it, in the head position they actually hold. The catalogue figure is a starting hypothesis. You are the variable that confirms or kills it.
Head Position Is Trainable
Head position is not a fixed property of an athlete, and this is the point we want to press hardest. It can be trained, and the most underrated component of that training is proprioception — the body’s awareness of itself in space.
Vision is one of your body’s key proprioceptive feedback channels, and one that the untrained athlete heavily relies on to stay upright. Training the other proprioceptive channels reduces the reliance on vision, just to complete the basic task of remaining on the road. When you have the ability to control every movement of the bike instinctively, your ability to optimise your head position improves out of sight [no pun intended]
Ken’s drill of choice is one most athletes underrate — and probably one most athletes avoid: free rollers, ridden in your full TT position. Rollers force the body to find balance from sources other than the visual input. After consistent rollers work, athletes who previously could not hold a low head position on the open road begin to. Their vision is no longer doing the heavy lifting of the proprioceptive system.
Long Tail, Short Tail: Discipline and Terrain Decide
One of the most visible differences between TT helmets is the tail. A long-tail closed-shell design is built to allow air to smoothly flow off the back of the head and onto the rider’s shoulders and upper back. It works beautifully — as long as the head is held in a consistent position, where the helmet smoothly transitions to the shoulders.
The silhouette of the helmet and the silhouette of your body should blend and form one continuous body. This isn’t absolutely true all the time, but it is a good subjective indicator of helmet performance. Some helmets are designed to have a small gap between the helmet tail and the torso, but the helmet tail should generally form a continuous line with the torso. The bigger the discrepancy in those silhouetts forming a continuous shape, and it is a pretty valid assumption that the helmet performance is suboptimal.
And because head position plays so heavily into the silhouette of the helmeted head, evaluation of these can readily be done on the rollers - The same exercise used for improving position quality.
It's actually quite hard to get a representative position on an ergo [fixed], even with elite athletes. We see this all the time, where your bike fit in the lab looks nothing like the position the athlete holds on the road. It's the same with helmet evaluation, so you need to be cautious with any static cycling posture and look to validate a decision in a more dynamic environment.
The discipline matters here. A pure individual time trial is short enough that a well-drilled rider can commit to a single locked position from start to finish. An Ironman bike leg is a different beast. Over four-plus hours, fatigue creeps in, the head drifts up, the posture loosens. A helmet that punishes any deviation from one perfect angle is a helmet that is fast for the first hour and slow for the last two. Forgiveness of head movement is worth more in long-course racing than in a 40-minute effort.
Terrain is the other half of the question, and the most practical way to think about it is simple: count how often the course pulls you out of the aero position. On a flat, fast course where you stay down for hours, a long tail earns its keep. On a course with repeated climbs — where you are up out of the bars, head high, looking up the road — every one of those moments turns the long tail into a liability. Raised and tilted back, it catches air rather than slicing it. The more climbing and the more technical descending a course throws at you, the more a shorter or more rounded, position-agnostic helmet makes sense.
The Wide-Helmet Era
It's not just tail length that impacts helmet performance. The clearest evolution in TT helmet design over the past few seasons has not been the tail - It has been width. A wave of much wider shells — Rudy Project’s wide platforms, the MET Drone raced by UAE Team Emirates, and similar designs from other brands — has changed how riders think about the problem.
The logic of a wide helmet is that it can fill the troublesome gap between the head and the shoulders more completely, and that a broader shell tends to behave better across a range of shoulder widths. This is especially useful for triathletes, where shoulder musculature is far more developed than the UCI counterpart. The broader the rider’s shoulders, the more there is for the helmet’s airflow to manage cleanly, and the more value a wide shell can return. The assumption that the longest tail is automatically the fastest helmet has quietly been retired. For a lot of riders, it simply isn’t true anymore.
Wide helmets are so 2024. Actually, the wide-helmet craze started in 2021 with the Tokyo Olympics — arguably even earlier with the POC Tempor — but in 2024–25 they really came into vogue with practically every brand offering a solution. And they tend to work.
Trimmed Visors and the Position Conflict
The next chapter of the wide-helmet story has been the trimmed visor. Wide helmets expand the volume outward, a deep helmet extends the volume downward and the visor is a critical part of expanding the depth. Filling in the volume is fast in the abstract, but it creates a very real problem. In the optimum head-down position, the lower edge of the visor runs straight into the forearms. This is a problem in a static sense for the head position that can be achieved, but an even bigger problem on the road, when bumps force the hands into the visor and can cause it to dislodge, or the helmet to reposition.
In my opinion, the trimmed visor is the icing on the cake with the dramatic helmet changes that we have seen. The visor trim is simply a cavity in the visor to allow the head to sit in an optimal position, with the outer edges of the visor splaying over the forearms, wrists or hands. A trimmed visor has the potential to make a troublesome design function extremely well, adding versatility to a helmet option.
In practice, this means the trimmed-visor option is most useful for athletes whose realistic head position is already low. If your race position carries your head a touch higher, you may not need the cavity at all. Consider this when looking at helmet options.
Ventilation: The Decision Kona Makes For You
Everything above assumes the limiter is air. In a hot race, it is not — it is heat. A perfectly sealed aero helmet is, by design, a closed box on top of the part of you that most needs to shed temperature. When the body cannot dump heat fast enough, it reprioritizes away from propulsion, power fades, and the run is mortgaged long before T2. On a hot course, ventilation stops being a comfort feature and becomes performance equipment.
Kona is where this is least negotiable, and the 2024 men’s race offered an unusually clean illustration. Sam Laidlow and Patrick Lange both raced in the same Ekoi helmet. Laidlow ran his fully sealed, with no ventilation, and rode a blistering, record-setting bike split off the front of the race — before his day came apart on the marathon, where he was reduced to walking. Lange raced the same helmet with a vent hole cut into it for cooling, and went on to win.
It would be too simple to say the vent hole won Patrick Lange the race; an Ironman is decided by dozens of variables, and two athletes are never running the same engine on the same day. But it is a vivid, real-world reminder that in Kona-grade heat, the cooling decision is a performance decision. The most aerodynamic configuration of a helmet and the fastest configuration of a helmet are not always the same object, and on the Queen K, they often are not.
One of the benefits of the bigger helmet designs with larger visors is that heat can escape. When the visor sits close to the face can feel very claustrophobic, especially in hot and sweaty environments. The more open design of the latest crop of helmets seem to allow better thermoregulation, with less of a barrier to microcirculation of air in front of the face. But it is also fair to say, for the likes of Kona, you would happily accept any ventilation channels that have been designed into a TT helmet and there needs to be an absolute priority given to thermoregulation more generally, with the garment that is worn. A ventilated helmet won't make up for fabrics that should never be used in heat and humidity.
Putting It Together
Helmet choice for Ironman and time trial is a chain of dependent decisions, and the order matters. Start with the position you can genuinely hold — and train it. Then weigh the discipline and the terrain. Then choose the shape and width that suit your build, rather than the one with the longest tail or the loudest marketing. Consider whether a trimmed visor unlocks a wider helmet for the position you actually race in. Then, last and decisively, for hot races, sort the ventilation for the conditions you will face.
There is no perfect candidate. You have to try the options you can get, with those first two points — head position and proprioception — front of mind when you try.
The wide-helmet era has given riders more good options than ever. It has not changed the method. Test the helmet on you, in your position, in conditions that resemble your race. The fastest helmet is the one that is fastest for you on the day — and in Kona, the one that still lets you run.
And to finish where Ken started: head position is a dynamic thing, and it is trainable. Do everything you can to improve your own form, and don't look at a TT helmet as "bolt-on aero".
Special thnaks to our testing and development partners - Streamlines Aero, the Australian Centre for Sports Aerodynamics, Adaptive Human Performance. Athletes Jake Birtwhistle, Natalie Van Coevorden, Matt Burton and Jordy Villani.
