Quote:
Originally Posted by gsak
I may be wrong but i think it has something to do with sweat/toxins etc reacting with the polystyrene liner inside the lid.As such it is five years from when the helmet is first used  . |
Correct.
Arai recommend you replace at the 5 year mark, and the ACU and FIM will not allow you to race with a helmet that is over 5 years old. Just about every helmet made today has the date of manufacture on a label or embossed into something on the lid. On an Arai it's on the chinstrap coverings.
Even with modern materials 5 years is about the safe lifespan of a helmet, besides, after 5 years of continuous use on my noggin they are ready for the bin anyway.