What is a snell rating?
Helmets meeting Snell Standards provide the highest level of protection available. Snell Standards significantly surpass those set by the U.S. Department of Transportation (DOT), the American National Standards Institute (ANSI), the American Society of Testing Materials (ASTM) and the U.S. Consumer Products Safety Commission's 16 CFR Part 1203. In order to continuously monitor the quality of helmets being sold to the public, Snell purchases and tests samples of currently certified helmets from the marketplace. These helmets are tested only in Snell labs by Snell technicians. Should a currently certified helmet fail, the helmet manufacturer must take corrective action to Snell's satisfaction.

What are the differences between snell SA and snell M standards?
SA Standard was designed for auto racing while M Standard was for motorcycling and other motorsports. There are three major differences between them:

1.      SA standard requires flammability test while the M standard does not;

2.      SA standard allows narrower visual field than M standard (Some SA helmets may not be street legal);

3.      SA standard has rollbar impact test while M standard does not.