How should a cycle helmet fit, and when should I replace it?

Getting a helmet level, snug and correctly strapped takes two minutes and is the difference between protection and decoration — plus the honest rules on when one is finished.

Difficulty: beginner
Time: 10 min
Read: 5 min
Safety: caution

Short answer

Level on the head with about two fingers' width between eyebrow and rim, side straps forming a V just under the ear, and the chinstrap tight enough that only one or two fingers fit underneath. With the strap done up, the helmet should not move more than a centimetre when you push it hard in any direction. Replace after any significant impact, and when it no longer fits or the shell or straps are damaged.

Wearing a helmet is not compulsory anywhere in the UK for any age. If you choose to wear one, it only does its job in a fairly narrow band of positions, and a very large proportion of the helmets you see on the road are worn outside it — usually too far back, usually too loose. Fitting one properly is quick and free.

Safety

A helmet worn tipped back exposes the forehead, which is the part most likely to hit the ground, and a loose helmet moves out of position before it is needed. A helmet that has taken a significant impact is finished even if it looks undamaged, because the foam crushes permanently and cannot absorb a second blow in the same place.

What you'll need

A helmet in the right shell size
A mirror or a second person

Step by step

Get the shell size right first.Measure round the head about a centimetre above the eyebrows and compare with the maker's size range. The retention dial adjusts fit within a size; it does not fix a shell that is the wrong size. If the helmet is oval and your head is round, or vice versa, try a different brand — pressure points mean the wrong shape.
Sit it level.The rim should be roughly parallel with the ground, low at the front, with about two finger widths between your eyebrows and the front edge. Tipping it back to look better is the most common error and it leaves the forehead unprotected.
Tighten the cradle.Turn the rear dial or adjust the cradle until the helmet grips all round without a pressure point. It should stay on your head, in position, with the chinstrap undone and you leaning forwards.
Set the side straps into a V under the ear.Slide the plastic splitters so the junction sits just below and slightly in front of the earlobe, with both straps flat and not twisted. This is what stops the helmet rolling forwards or backwards.
Do up the chinstrap properly.Tight enough that you can slip one or two fingers between strap and chin, and no more. Open your mouth wide: you should feel the helmet pull down. Trim and secure excess strap so it does not flap.
Do the movement test.With everything done up, push the helmet firmly back, forwards and side to side. It should move barely at all, and the skin of your forehead should move with it. If it slides, tighten the cradle and re-set the side splitters.
Check the standard marking.Helmets sold for cycling in the UK should be marked to a recognised standard — EN 1078 or an equivalent. Look for the marking inside; an unmarked helmet from an unknown source tells you nothing about what it will do.
Fit a child's helmet with the same rules, not a looser version.The same tests apply. Children's helmets have deeper rear coverage and lighter shells. Do not buy one to grow into, and take it off before playground equipment and climbing frames, where the strap is a strangulation risk.
Retire it when it is due.After any impact where the helmet hit something, even if there is no visible mark. If the shell is cracked or dented, if the foam is compressed, if the straps are frayed or the buckle is cracked, or if the fit system no longer holds. Otherwise, follow the manufacturer's guidance — many suggest replacement after several years as materials and straps age.

Tips

If you crash and the helmet hits anything, replace it. Manufacturers often offer a discounted crash replacement — ask.
Do not paint a helmet or fit stickers with solvent-based adhesives; some solvents attack the expanded polystyrene liner.
Store it somewhere that is not a hot car boot in summer. Heat degrades the foam.
A helmet with MIPS or a similar rotational-impact system adds a slip layer inside. It is a reasonable thing to want, and it never substitutes for correct fit.
For commuting, a helmet with a mount for a rear light or a peak is genuinely useful.

Common mistakes

Wearing it tipped back off the forehead — The forehead and the front of the skull are the most likely contact area in a fall over the bars, and tipping the helmet back is exactly what uncovers them.
Leaving the chinstrap slack — A loose helmet rotates out of position in the first fraction of a second of an impact, and then it is not where the impact is.
Keeping a helmet that has been dropped hard or crashed in — The foam works by crushing, and crushed foam does not spring back. Damage is often invisible from outside.

If it doesn't work

The helmet slides back when you ride

Cause: Cradle too loose, or side splitters set too far back — Fix: Tighten the rear dial and move the splitters forward until the V sits under the ear.

Pressure point or headache after an hour

Cause: Wrong shell shape for your head, or cradle over-tightened — Fix: Slacken the cradle slightly; if the pressure point remains, try a different brand with a different internal shape.

Straps constantly loosening

Cause: Slippery webbing and a worn splitter or buckle — Fix: Re-thread the strap through the buckle correctly and replace the helmet if the buckle no longer holds.

Sunglasses will not fit under it

Cause: Helmet sitting too low at the back or the wrong shape — Fix: Check it is level rather than tilted, and use glasses with straight arms that sit under the cradle.

Questions people ask

Is a helmet compulsory in the UK?

No. There is no legal requirement to wear a cycle helmet in any part of the UK, at any age, on any road. It is a personal choice.

How often should a helmet be replaced if it is never crashed?

Manufacturers commonly suggest a period of a few years because straps, buckles and foam age. In practice, replace when the fit system, straps or shell show wear, or after any impact.

Are expensive helmets safer?

Above the basic standard, extra money mostly buys ventilation, weight and comfort rather than a higher standard of protection. Fit matters far more than price.