How we test helmets
Every helmet sold in the UK and Europe must pass the same minimum safety standard, according to EN 1078. Passing tells you nothing about how well one helmet protects compared with another. HIPER is an independent rating developed by experts in brain biomechanics that tests helmets in conditions that represent real cycling crashes. It helps you choose a safer helmet, and helps manufacturers aim their designs at real-world safety.
The rating method
How a helmet is rated
Every helmet is tested with 12 impacts.
1
The impact
A headform wearing the helmet hits an anvil tilted at 45° at 6.5 m/s. The angle makes the head rotate, as it does when a cyclist's head strikes the road at an angle.
6.5 m/s
Around 20% faster than the European helmet standard (EN 1078), which tests at up to 5.4 m/s.
- 45°Anvil angle
- 4Places on the helmet
- 3Repeats at each place
- 6.5 m/sSpeedOur review of published studies found that cyclists' heads hit at speeds concentrated around 5 to 8 m/s. We test at 6.5 m/s, within that range.
- 45°AngleA cyclist's head rarely hits a surface straight on. In reconstructions and simulations of real crashes, the angles are concentrated between 30° and 60°. We test at 45°.
- 80%Flat surfaceIn nearly 80% of cases the head hits a flat surface, so we test on a flat anvil.
- 80-gritRough surfaceAbrasive paper on the anvil creates large friction forces and more head rotation. It represents the upper limit of friction, and CEN/TC158/WG11 has adopted it too.
Four places on the helmet
Each place makes the head spin mainly about a different axis through the centre of the head:
- X runs from the back of the head to the front.
- Y runs from side to side.
- Z runs from the neck up through the top of the head.
Front
Spins mainly about Y: a nodding motion.
Front-side
Spins mainly about Z: a turning motion.
Side
Spins mainly about X: a tilting motion, ear towards shoulder.
Rear
Spins mainly about Y: a nodding motion.
3
What the headform feels
Sensors inside the headform record how fast it speeds up and how fast it spins along the three axes, 20,000 times a second. The black line is the resultant, the combination of all three. In this front impact the head spins mostly about the Y axis, a nodding motion. The g-force is over in about 12 milliseconds, far quicker than a blink. Press play to watch the first 15 milliseconds 200 times slower, or drag across the charts.
Time 15.0 ms
Tap to show or hide a lineLinear acceleration (g)Resultant 0.6X 0.3Y -0.3Z 0.5 Angular velocity (rad/s)Resultant 16.7X -1.0Y 16.3Z 3.4 4
From the peaks to injury risk
The peaks go into two injury risk curves from the scientific literature. Peak linear acceleration, the g-force on the head, predicts skull fracture and bleeding on the surface of the brain. The Brain Injury Criterion (BrIC), worked out from how fast the head spins about each of its three axes, predicts injury deep inside the brain. The two risks are averaged into one risk for the impact. Every helmet is tested three times at each of four places, 12 impacts in all.
Linear injury risk112 g gives 13.6% Rotational injury riskBrIC 0.32 gives 15.8% 5
Weighted by where real heads are hit
Some parts of the head are hit far more often than others. We reviewed real cyclist crashes to find out how often each region is hit. Each place we test counts in proportion to how often that region is hit, so the rating reflects how crashes really happen. The front is hit most, so we test it at two places: the front and the front-side.
We do not test the crown. It is hit least often, and helmet standards already test it.
Source: Baker et al. (2023), n = 815 impacts. Head map after Baker et al. (2023); test locations are approximate.
FrontRearSideSideCrownHIPER test location
Share of head impacts
- Front38.2%
- Side28.7%
- Rear20.3%
- Crown (not tested)13.0%
6
The Protection Score and medal
Adding up the weighted risks gives the helmet's overall risk. The Protection Score is the overall risk turned around so that higher is better: a score of 100 would mean no risk. The score sets the medal. The medal lines are fixed, so a helmet's medal never depends on which other helmets we test. Every helmet sold in the UK must pass the EN 1078 standard, which guarantees a baseline level of protection, so every helmet we rate gets a medal.
Try it: move the slider to change the overall risk.
Protection Score77.0 /100
MedalGold
BronzeSilverGoldPlatinumDiamond