A bicycle helmet that folds into a bag solves a practical problem. If it is easier to carry, riders may be more willing to take it with them. The engineering challenge is making that convenience work alongside effective impact protection.
New research from Imperial College London has found that collapsible bicycle helmets provided less protection on average than conventional designs. But the results also show that folding mechanisms need not prevent a helmet from performing well: one collapsible model ranked second among the 30 tested.
All helmets in the study met minimum regulatory safety standards. The researchers stress that wearing a helmet remains safer than riding without one.
The team from Imperial’s Dyson School of Design Engineering tested 24 conventional helmets and six collapsible models available in the UK. Funded by The Road Safety Trust, the study assessed protection against both direct impacts and the rotational movements associated with angled collisions.
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The average predicted risk of linear injuries, such as skull fractures and focal brain injuries, was 24 per cent for collapsible helmets and 20 per cent for conventional models. These are estimates derived from the impact tests, rather than injury rates observed among cyclists.
The researchers found no difference between the two groups in average protection against injuries associated with head rotation. However, five of the six collapsible helmets finished in the bottom half of the overall protection rankings.
Weight emerged as an important design consideration. Collapsible helmets weighed an average of 461 grams, compared with 294 grams for conventional models, making them around 57 per cent heavier. Greater helmet mass was associated with increased predicted linear injury risk.
Technologies designed to reduce rotational head motion were also less common among the folding models. Only one of the six collapsible helmets incorporated rotational protection, compared with half of the conventional helmets.
A comparison between two versions of the same collapsible model illustrated the potential for improvement. The version fitted with the Multi-directional Impact Protection System, known as MIPS, ranked second overall. The version without it ranked 26th.
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That result points towards a development opportunity for manufacturers: reducing weight and incorporating rotational protection could improve performance while retaining the portability that makes collapsible helmets attractive.
To reflect common crash conditions, the team tested helmets at four impact locations, measuring linear and rotational head motion. Each impact was repeated three times with a fresh helmet sample.
The findings will inform Imperial’s Helmet Impact Protection Effectiveness Rating system, or HIPER, which gives consumers comparative performance information beyond regulatory pass-or-fail certification.
Its previous star ratings have been replaced with diamond, platinum, gold, silver and bronze medals, reinforcing that every ranked helmet has passed the European safety standard.
For designers, the study provides evidence about where improvements could make a difference. For cyclists, it demonstrates why neither a helmet’s price nor its ability to fold tells the whole story about protection.
“Are collapsible bicycle helmets as protective against head injuries as conventional designs?” by William Dawber and colleagues is published in Accident Analysis & Prevention.
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