In one comprehensive study of real-world impact performance based on research done for Motorcyclist Magazine, presented by Mr. Thom to the Motorcycle Safety Foundation, a $79.95 helmet certified to Transportation Department standards performed the best of the 32 tested, withstanding the most violent hits while transmitting as much as 67 g’s less impact force to the headform than a $400 Snell-certified helmet.

The other problem is, how much helmet will you wear. A good motorcycle helmet will generally provide more protection than just about any other helmet, but they are heavier and do not provide as much venting. This is OK for riding a motorcycle because in general you are not exerting as much physical energy as you would be on a non-motorized vehicle.

What are the differences between the SA, M and K standards?
The SA standard was designed for competitive auto racing while M standard was for motorcycling and other motorsports. The K standard was released to accommodate helmets used in karting. There are three major differences between them:

1. The SA standard requires flammability test while the M and K standards do not.
2. The SA and K standards allow for a narrower visual field than M standard (Some SA and K certified helmets may not be street legal).
3. The SA and K standards include a rollbar multi impact test while M standard does not.