How to choose the right shape for your aero helmet

The shape of an aero helmet is very influential because certain designs will make some triathletes faster but slow others down.

Often featuring a long tadpole-style tail, bulbous form, minimal ventilation and visor, triathlon aero helmets or time-trial helmets can make you more streamlined on the bike.

But they’re not the most cost-effective aero upgrade for triathlon and you don’t always need an aero helmet. When testing the best aero road helmets, we’ve found these lighter, more airy helmets can be a superior option. We’ve also been impressed by the best budget bike helmets. These show you don’t need to drop several hundred pounds or dollars on triathlom head protection.

Our wind-tunnel time has also underlined that aero helmet shape is individual. To be aerodynamic, you need to find one which compliments your body and riding style and position.

So if you are looking for a TT helmet, read on to find out how to choose the right shape for your aero helmet.

What shape should your aero helmet be?

Long or short tail?

Long tails aim to control the airflow over distance and guide it smoothly onto your torso. But they rely on meeting your back.

Short tail (aka stubby) designs give you great freedom of movement. They’re designed to be efficient while independent of your torso.

Because of the less extreme positions used in tri compared to time trialling, stubbies are often more suitable. In fact, long tail aero helmets are a rare sight in any triathlon race format these days.

Narrow or wide

For a long time designers pursued slim shapes with minimal frontal area so the helmet hits less air.

But recently, some brands have moved to wider shapes in order for the helmet to integrate with your shoulders. This relies on a lower position so that the helmet and torso work together though.

The extremely wide Giro Aerohead, debuted by Visma-Lease a Bike’s road cycling team in 2024, is the most striking example. But given the older Aerohead’s popularity in triathlon, it remains to be seen whether any triathletes will race this less ventilated version.

Smooth or dimpled

Surface features such as dimples and trips are designed to encourage ‘laminar’ airflow, where the air follows the shape of the helmet. Others (POC) go for the smoothest possible surface.

Remember that the helmet forms part of a bigger system and the rest of it is you, so your aero riding position and physiology (shoulder width, back length) are essential considerations.

How to choose an aero helmet for triathlon

The very best method is to book some wind tunnel time, where you can hone your position and try a number of helmets to evaluate if they reduce drag.

If you order a helmet, try it on at home while sat on your bike (ideally on a turbo, pedalling lightly) and have someone take photos of you from the front and side.

It’ll be easy to see if the shape integrates neatly or not, and especially if a long tail is stuck up in the air causing drag.