Buyers guide to road bike helmets

Just as there are a few different types of road bike, there are a few different types of road helmet. Here’s the lowdown.

There are three basic parts to a helmet: a polystyrene main form, an in-moulded plastic outer shell and the straps.


The polystyrene usually has some form of internal skeletal frame or honeycomb reinforcement system which helps keep it together during impact, which is handy when you’re sliding along the ground!


The plastic outer shell protects the inner against small dings and scrapes, like the knocks it gets when travelling and general wear and tear. It also helps protect the polystyrene from degradation from UV. The shell is also the place where the designers can put some style or colourway on to the helmet.


The straps anchor the helmet to the head and obviously stop it from falling off whilst riding or during a crash impact (well, as long as they are fitted correctly, which we will look at shortly).

Retention system

This is an inner plastic cage which provides a closer fit for the helmet. It usually takes the form of a dial at the rear which closes or opens the circle of the plastic inner cage.


There are other multi-pivoting designs that are initially trickier to set up but do offer very precise fit and security.

Each manufacturer has their own version of a retention system so check before purchase as they can be very different. Depending on how far down the helmet drops at the back and sides will affect the positioning of the dial so again check to make sure you are comfortable with this if going for a long drop helmet for more coverage.



Vents allow air to pass through the helmet to cool the head. They are strategically placed so as to maximise airflow but not at the expense of safety by reducing coverage.

Generally the more expensive the helmet the more the vents you get. Unless it’s an aerodynamically focussed helmet which have very few vents.



Removable inner pads are supplied with all helmets and they have a huge affect on comfort. They sit between the inner polystyrene layer and the head and although they are minimal in size they are strategically placed to increase comfort.

Pads also absorb sweat so make sure they are easily removable for washing. Most manufacturers supply spares with new helmets so don’t accidentally chuck them away when you get them!


Fit is the most crucial thing about a helmet. Never mind what you think it looks like; if it’s not comfortable you won’t wear it so there’s no point having it.

Here are a few pointers to help you get the best fit…

Measure your head. With a tape measure and measure the circumference of your head roughly 2.5cms (1”) above the eyebrows, do it several times to make sure, and check against manufacturer’s sizes (usually in cms). If you don’t have a suitable tape measure then use a piece of string and then measure the piece of string.

Put the helmet on and with the straps undone but the retention system dialled in, place your hands on the sides and try to rotate the helmet around the head. If it moves easily the helmet is too big, if it hardly moves then the helmet is the right size.

Straps. Anchor the straps just beneath the ears so they make a V shape from the side. This keeps the helmet in place better especially from frontal impacts. There should only be a one to two finger width between the strap and the chin, too loose and it’ll come off to easily on impact and too tight will be uncomfortable.


Different helmet types

Road – The majority of road helmets are light and well vented. The more you pay the lighter it gets and the better vented it is. Exotic materials are used for stronger but lighter lids – especially in the straps which can help prevent sweat build up over time.

Leisure – These tend to be slightly weightier as this is less of an issue and contain fewer vents. This is not to say they are bad helmets, the entry and mid price helmets of today are usually cheaper versions of the top end helmets from a few years ago and are packed with technology and innovation. More usually come with a peak which is handy sometimes so don’t throw it away.


Aero – This is the latest type of road helmet favoured by racers. They are more expensive, slightly heavier and contain fewer vents – all to achieve a more aero shape and performance. There are also aero lids that have vent sections that you can open and close on-the-fly.

Time Trial / Triathlon – These are the pointy helmets whose only purpose is aero gains so are only used in time trials and triathlons. They have a long pointy tail and few if any vents on the front so as to maximise aero properties.

Safety certification

There are several different safety standards which helmet manufacturers adhere to. It depends on the country and their testing standards. All helmets sold by Merlin Cycles are safety certified

Please note: Time trial / Triathlon helmets are not permitted in bunch racing due to their lower safety ratings.

Accessories and additional features

Certain helmets are supplied with various accessories which, depending on your needs, can be very useful or stored until you need them. Don’t just initially discard them because you never know.

Peaks – Most mountain bike helmets are supplied with peaks which do a great job of keeping mud, rain and sun out of the eyes. They’re not very aero and they get in the way of vision when riding on drop handlebars which is why they aren’t supplied with road helmets but they are handy accessories for commuting or some winter rides


Nets which cover the vents on the front of the helmet may seem a bit unnecessary until you use one. The amount of bugs they deflect is amazing and more than once I’ve deflected stinging insects away without the usual panic of removing the helmet or trying to shake them out while the helmet is still on and your still on the move, which never works either way!

Lights – Some helmets have lights integrated into the rear of the helmet. The Salice Bolt helmet (this is an old post and the linked content no longer exists) has a small LED in the retention dial which can be set to flash or steady. I’ve found this really useful on early morning and evening rides in the summer when you don’t necessarily need lights but it’s nice to have a little back up.

Visors – Many TT helmets and certain road aero helmets, such as the Giro Air Attack, are supplied with custom visors. These help aerodynamics and also safety as they keep the wind, bugs and dirt from the eyes, more prevalent when hammering along in the tuck position.

When to replace a helmet

Cycling helmets are designed to protect the head from impacts by absorbing the energy from a blow. This means the helmet gives up its life to protect yours. A helmet should be replaced after a serious crash even if there appears to be no major damage.



MIPS stands for Multi-directional Impact Protection System.

MIPS is a new way of making a helmet. Inside any helmet that’s equipped with MIPS is a ‘slip-plane’. Essentially this is a layer – or cradle – inside the helmet, against the head, that moves during an angled impact. MIPS allows the helmet to slide slightly on the head.

You can read more about MIPS in a previous blog of ours.

Is it worth spending the extra to get a MIPS-equipped helmet? It’s hard to say really. As with all new technology it comes with a high price tag. MIPS helmets will get cheaper over the next couple of years but for now they are too expensive for most of us.

Which road bike helmet should you buy?

Leisure riders don’t need to spend mega money to get a good helmet these days. Entry level helmets have great ventilation and retention systems and don’t weigh a ton either. The major factor here is comfort and whether you like the look of it or not.

Regular riders will appreciate a slightly lighter and better vented helmet especially if they are riding in the mountains where these factors come in to play.

Racers used to favour the lightest best vented helmets available which is still true for mountainous races or rides, but the current trend is for aero road shells where the marginal gains  from aero factors outweighs the slight weight penalty. Time trialists and triathletes will still favour the pointy full aero helmets for all-out speed.

Shop for road bike helmets on Merlin Cycles