Fast Bikes - - FEATURE -

Why do we need a hel­met? Well, when you have a crash, your head hits the deck, and your brain moves in­side your skull, bounc­ing off the in­ner sur­face of the bones. If that de­cel­er­a­tion force ex­ceeds a cer­tain level, the brain is dam­aged, and starts to swell up. Us­ing an inch or so of stiff-yet-crush­able polystyrene spreads out the de­cel­er­a­tion over a longer time pe­riod, re­duc­ing its peak value, and (hope­fully) pre­vent­ing brain in­jury.

An­other, less-ob­vi­ous in­jury path­way is an­gu­lar ac­cel­er­a­tion. That’s a posh way of say­ing jerk­ing and twist­ing mo­tions. If you’re slid­ing along the deck at 40mph, and your hel­met ‘catches’ on a rough bit of road, or a drain, kerb, what­ever, the hel­met jerks round, and trans­mits that force to your head. If the force is too high, then again, your brain suf­fers in­ter­nal dam­age – the tis­sue is ripped apart. That’s why firms like Arai are work­ing hard on mak­ing their hel­mets ‘smoother and rounder’. Hav­ing fewer edges in the lid­makes these twist­ing jerks less likely –a smooth, round shape can slide along a rough road more eas­ily.

Fi­nally, there’s the pen­e­tra­tion as­pect. This is un­usual in a crash – but the con­se­quences are gen­er­ally so se­ri­ous that they need to be con­sid­ered. Arai in par­tic­u­lar make a big deal out of hav­ing a very strong outer shell, with all the im­pact ab­sorp­tion tak­ing place in the liner. Some less-stiff ther­mo­plas­tic shells give good im­pact scores, be­cause the outer shell flexes, and ab­sorbs some im­pact. But if a weak shell lets a 4in rearset foot­peg stab into your skull, then it’s likely to be game over. So, pen­e­tra­tion re­sis­tance seems like a vi­tal part of the over­all pic­ture.

One com­mon fal­lacy that’s worth scotch­ing is about what hel­mets are there to pro­tect you from. They’re not there to save you if you hit a brick wall head first at 70mph, sadly. In­deed, even hit­ting a wall with your head at 20mph will prob­a­bly kill you: the lim­its on the size of a hel­met mean the shock-ab­sorb­ing layer can only do so much.

What hel­mets are mostly there for is to pro­tect your head from the ver­ti­cal drop if you fall off your bike – so a fall from around 5ft up. Gen­er­ally, in a crash, that’s the im­pact your head suf­fers – the bike low­sides and you slide off, or you get flung over the high­side and fall from a bit higher. Smack­ing your head on Tar­mac or con­crete, even at 5mph, with­out pro­tec­tion can eas­ily cause se­ri­ous, life-threat­en­ing in­juries. And it’s this that your hel­met is there to help with.

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