I joke in the store that if half of what's out there on replacing helmets was true, I wouldn't be working. I would be living on my private island... I'll address the "biggies" out there that I've heard...
Every five years you should replace your helmet...
Lets break this down. First, how would some lab-rat sitting in an office figure this out? I very much doubt that he came up with a magical equation that factored in what climate you ride in, how well you maintain your stuff, or how many times you'll drop, kick, or shine your helmet in a five year period.
So, where did the 5 year rule come from? Easy, from the Dealers wanting to sell you a replacement...lol. I personally think it came from the fact the SNELL (a safety standard) improves their standard every 5 years. It's easy to make the leap that every rider out there wants to be in the latest standard, even if the changes are small... Plus, it's a "number" they could belt out to keep people coming back. Also, many of the Manufacturers have a 5 year warranty period. Like the helmet will explode on impact if it's out of warranty...lol.
Answer - Look, if helmets had a shelf life, it would be printed on the box... If you take care of your helmet, there's no reason it can't last longer than 5 years. It's that simple. Now if your comfort liner is turning into dust (I've seen it), then you shouldn't need someone to tell you to replace your helmet.
If you drop your helmet, it needs to be replaced...
There are two types of shell material used in helmets. Plastic, and some variation of fiberglass, Carbon fiber, Kevlar (and everything in between).
First, plastic (thermoplastic to be fancy). This is the same stuff they make football helmets out of, and you don't see these guys tossing their helmets into the trash after every hit. Fiberglass composites are a little more tricky, but odds are that if you drop your helmet, the shell is fine.
What damages a helmet is your head inside during a crash. The Styrene inner shell is what does most of the work in a crash. As your head hits something, the Styrene compresses slowing your head (and brain). The shell does a bit of this, but is there mainly to prevent penetration and help distribute the blow over a wider section of Styrene. If your head isn't inside the helmet, no Styrene compression, no damage.
Answer -If you drop your helmet, and it has a plastic shell, look for cracks. If no cracks, it's most likely fine.
If you have a fiberglass shell, it gets a bit more tricky. The shell could have "spider web" cracks under the paint, softening the shell. This is a problem, since, like I mentioned, it's main job is to stop something from penetrating the helmet. I can say this, I've personally sent helmets away to be inspected and EVERYONE came back fine... Take that for what it's worth. The fiberglass shelled helmets are pretty tough.
Here it comes, the DISCLAIMER...
There's a MILLION ways you can damage your helmet, so there's no one on this small planet that can look at it, and say with 100% certainty, that your helmet is fine. I say use commonsense. If it was strapped to your bike lock, and the bike tips over on your helmet, the helmet is toast. If it tumbles off your back seat going 50mph, bounces down the street for a half mile, get a new helmet...lol.
