A helmet is one of the most important cycling accessories you can buy. Your brain is a valuable, vulnerable organ, yet it’s only protected by a thin layer of bone and skin. We were never designed to hit the roads at 50kph, or go hurling down rock-infested hills, so adding an extra layer of protection is an incredibly good idea.
We’ve put together a list that covers everything you need to look for in a bike helmet to make sure it will do its job properly.
Video: how to choose a road bike helmet
Video: how to choose a mountain bike helmet
There’s little difference structurally between the desired features of a road or mountain bike helmet, although the styles will vary. For example, mountain bike helmets tend to have integrated visors, while road cycling helmets don't, because they often impede vision when used with a drop handlebar.
And dirt jumpers, for example, will favour increased protection, while a cross-country rider will look for light weight and ventilation. Similarly, a road racer might prioritise aerodynamic qualities, while a commuter or weekend warrior will put protection and ventilation first.
No matter what style of riding you do, here's what you should be looking for in a bike helmet.
The primary importance of a helmet is protection, and there are plenty of government-instituted standards that they should all meet, which can vary between countries or continents. (In the US, helmets must be CPSC-approved; in Europe, it's the CE sticker you're looking for; in Australia it's AS/NZS.)
Most helmets are constructed from shock-absorbing expanded polystyrene. Its job is to sacrifice itself during a crash, so after a big impact you might see a cracked helmet – that’s the material doing its job. Once broken, do not use it again.
Nearly every helmet these days is in-moulded – the outer shell and protective inner material are moulded together – for extra strength. And systems such as Mips, found in certain mountain bike helmets, go even further, by offering additional protection against rotational impacts, which are far more likely when out on a ride.
The Scott Stego mountain bike helmet incorporates the Mips protection system
It's also now common to see mountain bike helmets offer increased protection with a deeper fit and greater coverage at the back.
When you’re working hard your head is one of the places that helps your body regulate heat, and ventilation is vital for keeping you cool as temperatures rise.
Ventilation usually takes the form of multiple exterior holes, or vents, through which air can flow directly to your head.
The GT Corsa road bike helmet has 22 vents and internal air channelling
It’s not just about how many holes can be formed in the outer shell though. Helmets should also feature well designed internal venting – air channels carved into the inner shell to direct air effectively over the hottest parts of the head. This air is then channelled to large exit ports, effectively your head’s exhaust pipes. With these in place, the helmets can easily stop your head from overheating on all but the hottest days.
Some mountain bike helmets feature larger, more open vent holes because mountain biking has a lower average speed than road cycling. The downside to these larger holes is that greater wind noise is created, which makes them unsuitable for road cycling.
Your helmet should have a comfortable, snug fit, without being too tight. Measuring your head will give you a good starting point. To do this, pass a tape measure around the circumference of your head, just above your ears. This should help you work out what size to try on first.
BikeRadar testers found the fit of the Giro Saros road bike helmet to be especially comfortable
Make sure you try on plenty of different makes and models. Helmets aren’t all the same shape internally, and some manufacturers have a distinct shape to their helmets – rounder, or more oval, for example – so you should be able to find one that suits your head.
Every helmet has a retention system, to ensure the helmet fits properly and stays in place in the event of a crash. Most adjustments are taken care of by either a turn-wheel of some sort or little ratchets that control the adjustable band around the head.
Bike helmet retention system, demonstrated on the SixSixOne Recon mountain bike helmet
Ensuring the fit is comfortable is the rear cradle – ideally shaped to hug the base of the skull to stop the helmet popping off the front of your head if you hit the back of it. The chin strap is also adjustable.
Padding is the icing on the cake when it comes to comfort. It can help with fine adjustment of the internal shape and wick sweat away from the head, and anti-bacterial treatments can prevent unpleasant smells.
More applicable to mountain bike helmets than road bike helmets, visors are there to protect your eyes against the glare of the sun and to stop raindrops getting in your eyes or on your glasses, but they shouldn’t obstruct your vision.
The Mavic Notch mountain bike helmet has a built in peak to protect the rider's eyes. This one is fixed, but they are adjustable on some helmets. Road bike helmets don't tend to have peaks or visors
Adjustable visors are worth looking out for too, so you can fine tune how much they sheild your eyes.
Finally, check to see if the helmet has a crash replacement scheme. Many suppliers offer subsidised replacements if your lid is damaged within the first year or two of ownership – which, if you’re particularly accident-prone, could be worth having. Terms and conditions vary though, so check the small print.