The issue isn't one of impact resistance, but rather providing the driver enough protection to get out of a car in the case of fire.[scratch] i find it strange that i can't use my helmet that i use riding a GSX-R 600 that's more dangerous and MUCH faster than my car but its not good enough to wear racing my slow car at a road course? [confused] [}]
SA helmets are lined with Nomex, fire retardant material, whereas motorcycle helmets are not.
Some clubs allow M rated helmets to be used given that drivers are only wearing long pants and long sleeve cotton shirts as opposed to full driving suits.
Personally, I think it is a bit overkill, but at the same time I see its purpose.