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One reason, and there are several is that the helmet spends a great deal if time in the sun and the UV attacks the outer shell. We have all seen what a lotnof exposure to the sun can do to many materials, even those that are claimed to be UV resistant. Very few man made materials are UV proof so after time they degrade.Plastics, composites and such all degrade with time. The time limits helmet makers put on their wares is aligned with predicted rates of degradation so that you know when a helmet could be considered less than optimum at protecting your noggen.Some people will choose to decide for themselves when a helmet isn't really suited to perform as they have better testing procedures, know more and the tin foil liners theybuse are so much better than what the engineers know and use.
Isn't the concern about the impact absorbing liner, ...
That's why, in particular, clubs with track days won't let you use a helmet that's over 5 years old.
Of course it could also be the legal liability thing again.
Fiberglass is forever. Polycarbonate may not be. But the weak link is the EPS liner. When I moved last year, cleaning out the garage uncovered three ancient helmets -- my Bell 500 and Star and an old Shoei -- all 20 to 30 years old. As soon as I lifted, them, the liners turned to a chunky black powder that ran out onto the floor.That's not going to happen in five years, of course, but the process begins sometime around the decade mark. Helmets aren't the only time-limited safety equipment. The ski industry has a five-year limit on ski bindings -- beyond that, manufacturers won't indemnify retailers targeted by personal injury suits. Insurers don't want the long liability tail. So no shop will test or service bindings that aren't on the five-year indemnification list.
If you helmet was as over designed as a boat hull, it would be too heavy to wear. <shrug>
As I see it the 5 year life span on helmets is due to two reasons, to sell more helmets and because by then the old one stinks.
This is a blanket statement and just isn't based on demonstrable evidence. Once again, I know I come off as a jerk when I say it, but my job is assessing failure of composites on boats. The theory that all fiberglass composites gradually degrade just does not hold water.
For the last 25+ years, I have always worn a cotton or silk cover...
Makes sense to me. My first Shoei, new in ...1985 ? was just fine through circa 2005, then the lining magically shredded itself, and came out in little fragments.
Pitch them after you have an accident.Maybe the assumption is that on average, a motorcyclist has a crash every 5 years?
I keep them for the memories........... ...
Took this directly from the UK Arai site as my RX-7 Corsair is now 8 years old and I wanted to know when I should start looking for a replacement.Arai helmets are handmade to the highest possible standard, and although after many years the outside shell can look as good as new, it�s the EPS polystyrene liner that loses its ability to absorb impact over time. Arai recommend replacing your helmet 7 years after date of manufacture and 5 years after date of purchase to maintain the maximum levels of protection.The EPS liner is effectively the shock absorber of your helmet, absorbing the force of an impact onto the shell. This is done by the cells in the poly styrene being expanded (EPS = Expanded Polystyrene) and filled with air to absorb impacts. Over time, even when not in use, these liners lose their air pockets incrementally, after 7 years, dropping the shock absorbing ability of the liner below Arai�s safety standards. This is why we declare the helmet due for replacement so it can properly protect you against impacts.
This is what I suspected was the part that is the issue.So, why can't I buy a $20 replacement liner for my helmet and keep the shell?If Schuberth would do that I'd go buy one in a heartbeat, or any other very expensive helmet out there.Seems a shame to throw away a perfectly good helmet just because some cheap 'packing foam' degrades over time.
Some reasons that might not be a good generalization:1. Bicycle helmets have a lot of ventilation spaces, so the pressure (psi) on the materials for a given impact is higher than for motorcycle helmets.2. While average riding speeds are lower for bicycles, downhill speeds can easily get over 40 mph.3. With some accidents, the speed that the 2-wheeled vehicle is going may not matter as much as the speed the car that hit it was going.4. Many motorcycle helmet impacts result from the rider's head hitting the pavement, when it's able to slide, rather than be stopped by something like a curb, so the impact in those cases is mainly a fall from six feet up.