How to Choose a Bike Helmet: Fit First, Then Features

Buy for fit, not for features. A helmet that is the wrong shape for your head, or that sits tipped back off your forehead, will not do its job in a fall — however much it cost and however many vents it has.

Work through it in this order:

• Measure your head in centimetres
• Compare that number with the maker's size range, not the label
• Set the fit system and the straps properly
• Check the standard mark inside the shell
• Only then start comparing ventilation, weight and extras

If you do nothing else, do the roll test with the straps done up. That single check catches most of the helmets that are sold to people but never really fitted to them.

You don't need much, but you do need the right few things. Trying a helmet on in the clothes you actually ride in takes ten minutes and saves a lot of guesswork.

A correctly fitted helmet sits level on your head, not tilted back like a sun hat. The front edge should be roughly two finger-widths above your eyebrows — close enough that your forehead is covered, high enough that you can still see ahead when you're in a low riding position.

The side straps should form a neat V just below each ear, with no strap crossing the ear itself. The chin strap should be snug enough that the helmet can't be pushed back off your head, and loose enough that you can swallow and turn your head freely.

Check the whole thing again with your glasses on and your head tipped forward in your riding position, because that's the moment a badly set helmet either drops over your eyes or slides back.

Once the fit is right, the differences between helmet types are mostly about coverage, airflow and what you want bolted to the shell. These are broad patterns rather than rules — plenty of helmets sit between categories.

In the UK, helmets sold for cycling are normally tested to EN 1078, the standard covering helmets for pedal cyclists and for users of skateboards and roller skates. A compliant helmet carries a UKCA or CE mark and the maker's details inside the shell.

The standard covers impact absorption on a test rig, the strength of the retention system and the fact that the helmet doesn't obstruct your field of vision. It is a floor, not a promise: the tests don't reproduce everything that happens when you come off, particularly the twisting forces involved in many real falls.

That's exactly why fit matters so much. A helmet held firmly in the right place can absorb the impact it was designed for. One that rolls backwards on the way down cannot.

Weight and airflow are the two things makers compete on, and both matter — but they matter after the fit is sorted, not instead of it.

• Helmet worn too far back. The front edge should be just above the eyebrows. If it covers your eyes at that height, the shell shape is wrong for you — try a different model rather than pushing it back.
• Chin strap left slack. It should be snug enough that the roll test pulls your forehead skin. Lengthen it slightly if it's uncomfortable, but not until it's loose.
• Straps twisted or the splitters in the wrong place. Undo the buckle, straighten the straps flat against your head and reset the V under each ear.
• A thick hat or hood underneath. It lifts the helmet off your head and stops the cradle gripping. Keep layers thin, or size up if you'll always wear one.
• Buying the same size as last time. Sizing changes between models and makers. Measure again each time rather than trusting the label on your old helmet.
• Reusing a helmet after a knock. Foam that has compressed doesn't spring back. If it took an impact with your head in it, replace it.

Replace a helmet after any impact where it took the force — including one where you hit the ground and the helmet looks fine. The foam liner is designed to crush once, and it doesn't recover.

Retire it sooner than you'd like if you find cracks in the shell, crushed or flaking foam, frayed or stretched straps, or a buckle that won't hold. Follow the maker's own replacement guidance in the manual, and be stricter with a helmet that lives in a hot car, a shed or a damp bag, because heat and sweat age the foam and the padding.

A helmet you've used hard for several years is worth replacing even without a crash, and any helmet involved in a crash should be replaced straight away.

The method is the same, but the tolerances are tighter. Measure a child's head rather than guessing, and check that the helmet sits level and low enough at the front without covering their eyebrows or blocking their view upwards.

Children often end up with a helmet that has been sized up to last, which means it rocks or sits too high. A helmet that fits now and is checked every few months as they grow is the better trade. Check that the straps don't rub their neck, that the buckle can't be undone by them mid-ride if that's a concern, and that the helmet doesn't sit on top of a hood or a thick winter hat.

For anyone else — a partner, a parent — the roll test is the fastest way to spot a bad fit. Ask them to tip their head forward and shake it gently; if the helmet moves independently of their scalp, the straps need adjusting.