a 900???? dude... how old is that thing? You know the safety rating is void after like 5 years....
Shoei and Arai both have a 5 year warranty. That said, they both state, 5 years from date of purchase or 7 years from date of manufacture is useful life, and of coarse no crashes on helmet. That one terminates the life of helmet.
Shoei does offer a service to inspect helmets, theirs of coarse. Just costs shipping. Have done this with two dirt bike helmets after crashes. One failed (knew it would), the other was ok.
Biggest concern is care. If you use your helmet daily, in the sun (UV damage), sweat a lot (chemical damage) this is what reduces the life of the helmet.
The EPS (expanded polystyrene) liner is the major protection in the helmet. If this damaged, throw the helmet away. This material will most likely not be damaged in a drop, since there will be nothing on the inside to compress the EPS, unless you have a bowling ball inside. However, if the shell cracks, that will damage the EPS, and again throw it away.
They also say, that a helmet that is properly stored, cool, dry, ventilated, and dark, the helmet life is not compromised until first use.
I tend to push the limits a little farther to 10 years. Used 2x per week (rotate through multiple helmets), padded liners cleaned monthly, stored in air conditioned closet in manufacturer's bag, never in the garage, don't hang helmet from pegs close to engine heat source, wax helmet to protect from UV rays. That translates to a new helmet every 3 years and retire the oldest one.
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