Well, all helmets meet the same standards, and I don't think those
standards have changed since the "Which" article was written.

The Which article noted a tendency for helmets that meet the European
std not to meet the American standard, and vice versa, but some did meet
both.

The best rule is NOT to get a "good one". What makes a helmet "good" is
usually being lighter and cooler than a cheap helmet. This is achieved
by using as little styrofoam as possible, so an expensive helmet is
probably even less protective than a cheap helmet, even though both meet
the same stds.

There is some question about whether it really is necessary to replace a
helmet every x years as some people recommend. In practice the
styrofoam is unlikely to degrade from UV radiation. However, one
current theory about why helmets are so ineffective in practice is that
they are not kept tightly enough in position. It might be, so the
theory goes, that putting on and taking off a helmet over and over again
gradually compresses the material inside, thus making the helmet loose.

The same theory emphasizes that the chin strap MUST be kept tight. If
you can open your mouth to talk, the strap is probably too loose.

Adding a helmet to your head makes it larger and heavier than normal,
thus upsetting your reflexes that move your head out of the way of
impacts. Thus you will hit your head more with a helmet than you would
without. This doesn't matter though, because of that very helmet. Don't
assume, though, that in the impacts you are now having the helmet is
saving your life.

Jeremy Parker