Crash Hats — Helmet Safety, Standards & Technology

The Problem

An Industry That Keeps You in the Dark

When a helmet is sold, or even displayed by a retailer, there is no legal requirement to let the consumer know how well a helmet performs. If everyone buying a helmet bought the one offering the highest level of protection, many more lives would be saved.

The UK's SHARP rating is the closest thing we have to a performance rating, but retailers have no obligation to display the rating alongside the helmet. The SHARP rating is also only for motorcycle helmets and doesn't properly factor in a helmet's ability to handle rotational forces.

All of this needs to change.

Photo credit: Tom Sykes crashing at Thruxton — a powerful reminder that a crash can happen to anyone, at any speed. The helmet you choose matters.

Mechanics

How a Helmet Works

Simple helmet diagram showing shell, EPS and comfort liner layers

A traditional helmet consists of three layers. From the outside: the shell (visible outer layer), the EPS (expanded polystyrene) layer, and the comfort liner — the padded inside. More modern helmets feature layers of differing-density EPS, and some add a fourth layer to handle rotational forces.

As the helmet impacts, the outer shell spreads the force over a wider area, distributing it across the EPS layer. The EPS then absorbs and disperses the impact energy — reducing the peak acceleration force your head experiences because it decelerates over a longer time. This hopefully keeps your brain from slamming into the inside of your skull.

Slow your head too quickly (EPS too hard) → deceleration forces become injurious or lethal. Not slow enough (EPS too soft) → your skull effectively hits the outer shell. The EPS is the magic that saves lives — but not all EPS layers are equal.

It's worth noting that the exterior shell also plays a vital role: it needs to work with the EPS layer. Shells can be too thick, too hard, too thin or too soft in any given circumstance, so manufacturers try to cover a broad range which means it might not be optimal under all specific circumstances.

Brain Science

Rotational Forces

This is a relatively new area of focus when it comes to brain injury, largely due to advancements in technology. Diffuse Axonal Injury (DAI) occurs when the head moves but the brain stays behind. Sudden and violent rotational/torque forces cause the skull to rotate while the brain lags behind, tearing axon fibres. This tearing disrupts communication and chemical processes in the brain.

DAI is one of the most common and devastating types of traumatic brain injury. It's a major cause of unconsciousness and persistent vegetative state. In severe cases, the majority of patients do not regain consciousness.

Why This Matters for Motorcyclists Oblique/angled impacts with the ground typically result in rotational/torque forces. Any forward movement you carry will likely result in your head wanting to roll as soon as the helmet contacts the ground. That sudden rotation is the torque force that causes DAI.

Protection against these forces is relatively new to the helmet industry. Quite a few cycle helmets now offer this protection. Very few motorcycle helmets do. FIM FRHP and ECE 22-06 are the only current standards that require helmets to handle torque forces — and at time of writing (2021), only around 20–30 helmets meet these standards.

Innovation

Technology

With the exception of MIPS in the cycling world, Kali Protectives seem to be one of the only companies putting any real new technology into helmets. Composite Fusion, Low Density Layer and Carbon Nanotubes are just three technologies they're investing in. The company CEO (Brad Waldron) is quite open about the industry, standards, and what they're doing to make helmets safer.

Conehead EPS

Invented by physicist Don Morgan, this is a coned layer of EPS of a different density. As cones are crushed, their density increases — providing variable resistance matched to impact severity. Read more at Conehead Helmets. Incorporated by Kali Protectives into all their helmets.

Brands using Conehead: Kali, Head, Scott Sports SA, Mammut, Cannondale, POC, Triple Eight, Fly Racing, Acerbis, Leatt, Foxhead and more.

In-Shell Moulding Construction

Traditional construction sees the outer shell and inner EPS layer built separately, then glued — creating tiny gaps. Kali Protectives mould the EPS layer inside the composite shell, eliminating those gaps. This removes the "double spike" in g-forces caused by the shell and EPS not working together from the point of impact. Kali call this Composite Fusion.

Crumple Zones Claimed

Claimed to be present in Shark helmets — borrowing from automotive safety engineering. The idea is that like a modern car, the helmet structure progressively absorbs impact energy. No supporting technical data appears to be publicly available from Shark on how this is implemented.

MIPS Rotational

A low-friction layer between the comfort liner and EPS layer. In a collision, it allows the helmet to slide independently around your head — reducing the rotational energy transmitted to the brain. Best understood by visiting the MIPS protection website.

LDL Rotational + Linear

Another Kali Protectives invention — the Low Density Layer. Similar in goal to MIPS but vastly different in design. It's more than just a slip layer; it offers reduction in both rotational and linear forces. Read real-world data on Pinkbike →

Glancing Off Arai

Arai's claim is that by making helmets smoother and rounder, the helmet glances off an object rather than digging in, lowering the coefficient of friction. This would only benefit oblique impacts. Any change in velocity due to the glance still results in acceleration — and there doesn't appear to be any data publicly available to support the effectiveness of this approach.

Safety Certification

Standards

Terminology: g = g-force. One g is the acceleration due to gravity at Earth's surface — defined as 9.80665 m/s².

You should know that current helmet standards are still largely based on historical research done in the 1970s. Scientists determined how much force was required to fracture the skull of a cadaver, and any force less than that was considered survivable — approximately 300 g. This was long before concussion was considered a serious head injury.

During certification, if the headform inside the helmet experiences a peak force of 275 g or more, the helmet fails. Below 275 g, certification is granted. Now here's what most people don't know:

10g Minimum g-force at which serious brain injury can occur

Converting 275 g using Newton's second law (F=MA), with the average human head at 4.5 kg: F = 4.5 kg × (275 × 9.80665 m/s²) = 12,135.7 Newtons — equivalent to 1,237.5 kg or 2,728 lbs of force. Really good helmets will come in at under 100 g in impact tests.

Only FIM FRHP and ECE 22-06 require helmets to handle rotational/torque forces. Both are new (2020 onwards) and no road laws yet require compliance with these standards.

Motorcycling Standards

FRHP FIM Racing Homologation Program — required for all WSBK and MotoGP helmets

Impact velocity: 8.2 m/s and 5.0 m/s
Peak acceleration limit: 275 g and 208 g
Specific pre-determined impact test points
Oblique impact test
Single drop test
Penetration test

ECE 22.06 New UN standard — required for new helmet designs in Europe and UK from January 2024

Impact velocity: 8.2, 7.5 and 6.0 m/s
Peak acceleration limit: 275 g, 275 g and 180 g
Specific pre-determined and random impact test points
Multiple drop tests
Oblique impact test
Penetration test

ECE 22.05 Older UN standard — all helmets sold in Europe and UK must comply

Impact velocity: 7.5 m/s (16.8 mph)
Peak acceleration limit: 275 g
Specific pre-determined impact test points
Single drop test
No penetration test

DOT FMVSS 218 US standard — required for helmets sold in America

Peak acceleration limit: 400 g
Accelerations >200 g must not exceed 2.0 ms cumulative duration
Accelerations >150 g must not exceed 4.0 ms cumulative duration
Impact test points anywhere on upper half of helmet
Double drop test
Penetration test
Dropped onto a spherical hemisphere

Snell M2010 Optional certification by independent Snell Memorial Foundation

Impact velocity: 7.75 m/s (17.3 mph)
Peak acceleration limit: 275 g (lower for XL and XXL)
Impact test points anywhere on upper half of helmet
Double drop test
Penetration test: 3 kg dropped from 3 m
Dropped onto a spherical hemisphere

SHARP Rating British government scheme rating helmets 1–5 stars for protection

Established 2007 by British government
Rates helmets 1–5 stars based on protection performance
Tests at higher impact velocity than ECE 22.05 required
Does not currently rate rotational force protection
See the dedicated SHARP section for full detail

ACU Gold Required for UK track riding

Tougher requirements than ECE 22.05
A helmet with only a 3-star SHARP rating and poor impact performance can still be awarded ACU Gold
An improvement on ECE 22.05 but not truly rider-safety focused at track level

Cycling Standards

EN1078 European cycle helmet standard

Drop height onto flat: 1.5 m
Drop height onto kerbstone: 1.5 m
Peak acceleration limit: 250 g

CPSC American cycle helmet standard

Drop height onto flat: 2.0 m
Drop height onto kerbstone: 1.2 m
Peak acceleration limit: 300 g

Snell (Cycling) Optional independent certification for cycle helmets

Drop height onto flat: 2.2 m
Drop height onto kerbstone: 1.3 m
Peak acceleration limit: 300 g

Conclusion on Standards: They're inadequate.

They are so old and outdated that they're really not doing the industry or consumer any good. They need to be improved, and helmet manufacturers need to be pushed to sell helmets that offer far better protection.

While not a standard, and despite its shortcomings, the SHARP rating is currently the best way of determining a helmet's ability to protect your head when it all goes wrong.

Rating System

SHARP

SHARP was established in 2007 by the British Department for Transport after research (COST 327) revealed huge differences in real-world safety performance of available helmets. Its objective is to give clear, impartial advice on the relative safety performance of helmets. It rates helmets on a 1–5 star scale.

SHARP conducts 30 linear impact tests onto flat and kerb-shaped anvils, plus 2 oblique impact tests to establish a coefficient of friction. The oblique test impact velocity is 8.5 m/s. SHARP tests at a higher impact velocity than required by regulation — approximately 30% more energy input than ECE 22.05.

ECE 22.05 tests at 7.5 m/s (27 km/h). SHARP tests at 6.0, 7.5 and 8.5 m/s — covering low, standard and high-energy scenarios.

SHARP Test Matrix

#	Speed	Anvil	Test Site	Helmet Sample

Impact Zone Colour Code

Colours represent peak acceleration during impact at 8.5 m/s — approximately 30% higher than ECE 22.05 requirements.

Colour	Peak Acceleration
	Up to 275 g — the ECE 22.05 test limit at 7.5 m/s
	Up to 300 g — British Standard limit, max for 5-star rating
	Up to 400 g — the DOT test limit at 6.0 m/s
	Up to 420 g
	Up to 500 g
	In excess of 500 g

How SHARP Calculates a 5-Star Rating

32 linear and oblique impact tests are completed for each helmet model.
Coefficient of friction of the helmet shell is calculated using oblique impact test results.
Linear peak g and coefficient of friction are used to calculate the equivalent oblique peak g.
Peak g values are used to predict the risk of fatal injury for 30 linear and 15 oblique impacts.
"Importance" weighting for impact configuration is calculated using distributions of impact location, shape and speed.
Injury risks are weighted according to the impact configuration "importance".
Total risk for each helmet at each speed is calculated.
Exposure population is applied to the risk.
Final SHARP safety rating is assigned.

"Any helmets falling within the 5 Star rating band are subject to additional criteria; if the peak acceleration seen in any valid linear impact test performed against the flat anvil is equal to or greater than 300 g, the rating is modified to 4 Stars." — DfT: The Safety Helmet Assessment and Rating Programme – Procedure for calculating the SHARP safety rating

While SHARP does conduct oblique impact tests, there is no scale or rating of a helmet's effectiveness to handle rotational forces — and a lack of rotational force technology will not be detrimental to a helmet's star rating. There has also been some academic criticism of SHARP's testing methodology.

See the Further Reading section for links to the critical evaluation by Dr N.J. Mills and the DfT's published response.

→ Visit the SHARP website

Buying Advice

Which Helmet?

The million dollar question — but if you've read through all of the above, you're beginning to realise it's not that simple.

Which Brand is the Best?

That is up to you to decide. The authors of this website favour Kali Protectives because their helmets perform exceptionally well in tests, they do their own research, they genuinely care more about saving lives than sales figures, and because of their openness about their helmets, standards and testing. They also put their technology into all of their helmets, not just a select few.

Note on Kali and ACU Approval

Unfortunately Kali helmets are not ACU approved — not because they didn't make the grade, but because the ACU has never tested them. This means that if you want to venture out onto a race circuit in the UK, there's a chance you won't be allowed to.

How to Choose a New Helmet

Buying a new helmet is difficult. There are so many options and price gaps between upper and lower ends can be as much as £800.

Pro riders get paid a lot of money to wear a helmet. It's part of their job and they gamble that sponsorship money is worth the risk. Manufacturers know this and it's in their best interest to provide riders with their best-performing helmets. This doesn't mean all their helmets offer the same level of protection — and it doesn't mean the race replica on the shelves is the same helmet.

As a consumer you receive nothing in return for wearing a particular helmet. Styling, noise levels, initial feel and who else wears the brand means nothing in an accident. None of the big names — Shark, Arai, AGV, Shoei — publish anything about what makes their helmets safer than competitors. It's all ventilation, viewports and comfort. None of which will help you in a crash.

So Which Helmet Should I Buy?

Simply put: the one that in a crash transfers the least amount of impact energy to your head. Check the SHARP rating before buying. Any 5-star helmet should be at the top of your list.

Sadly manufacturers aren't keen to publish their test data. The model worn by a pro rider is likely to perform substantially better than the model you can afford, and manufacturers know this. Luckily SHARP have done some of the leg work for us.

What About Helmet Fit?

All the science and padding in the world will do very little if your helmet is too big. When trying a helmet on it should be tight — almost too tight, because the internal soft lining will bed in and loosen up. When it's on, you should be able to shake your head from side to side without the helmet moving independently. If it does, it's probably too big.

What About Price?

There's a perception that cheaper helmets can't offer the same level of protection as helmets three, four, five, even ten times more expensive. That's simply not true. A helmet is basically a spherical beer cooler — made from the same stuff, at least partly. The only way to know how well a helmet truly performs is to test it and look at the results. A cheaper helmet can perform just as well as an expensive one. Brand means very little. Test results don't lie.

Get In Touch

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Have a question, found an error, or want to contribute information? We'd love to hear from you.

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About this site

Crash Hats was created to educate motorcycle and cycling helmet buyers. All information is sourced from people in the helmet industry and publicly available research.

We have no commercial relationships with any helmet manufacturer, marketing company, or testing facility. All opinions are our own.

Find the SHARP database at sharp.dft.gov.uk to check ratings for specific helmets.

ProtectYour Head.