Originally Posted by dkmura

SA-rated helmets must pass multiple impact tests that M-rated helmets do not. Snell ratings are based on their use, and Special Application (SA) helmets are typically used for auto racing. In the event of a major car crash (vs. a bike crash) there's a higher chance of multiple impacts (ie. rollovers) in which the helmet needs to protect the head repeatedly. The M-rated helmet is rated to take one major impact only. As you mention, a fire resistant interior is part of that rating, but if you ever need THAT, you're in bad shape already! Passing those tests adds up to a more expensive helmet!