This is a topic that gets pretty interesting. Everybody knows that if your helmet takes a big impact it needs replacement. What a lot of people don't realize is that the DOT and SNELL ratings on helmets are based on street conditions, and we aren't necesarily well served by that.
A friend of mine is involved in trying to get different ratings for dirt helmets. He's got a kid that got a couple concussions in racing. In dealing with that, he's hooked up with a brain doctor that is convinced that dirt bike helmets have padding that is far too hard to protect a racer from the types and frequency of impacts that they encounter. The medical dudes are learning a lot lately about how a concussion affects the brain, and how bad it is to suffer another one within a certain time period from the first. My kid has suffered concussions in hockey, and one from riding. And in fact has been diagnosed with a learning disability that they feel is almost certainly the result of a head injury.
This hard lesson tells me protecting the head is pretty danged important. Unfortunately, I think in my son's case the injury that did the damage had nothing to do with sports, and happened when he was a little tiny baby and fell on his coconut while climbing around like little tiny babies do.
So, what does this mean when buying a helmet? Well, lots of stuff. From what I have learned, the "helmet health" is more important than I used to think, and it should be replaced every few years because the internal shock-absorbing material degrades over time. But, on the other hand, the helmet seems to have to be somewhat unsuitable for our use in order to acheive a rating that we are told to look for.
Does a helmet sitting in a box in a climate controlled bike shop for a year or two degrade at the same rate as one sitting on a sweaty noggin and subjected to fuel and solvent fumes? I kinda doubt it.
I would say if you can get a good quality left-over helmet, go for it. Generally the more expensive helmets are lighter and can prevent some types of neck injuries, but those are generally seen in race car impacts..
err,, but hey, less weight on the noggin is bound to keep you fresher and more likely to not screw up..
Sorry if this confuses you more than helps you.
