Motorcycle Snell M rated helmets are not usually allowed for track days due to the requirement for an SA rated helmet for cars. This has to do with impact ratings and the fact that SA helmets are designed to absorb multiple impacts (being tossed like a rag doll inside your car, hitting roll bars, etc) vs a motorcycle helmet that typically absorbs only a single impact.
If you have to have just one helmet, you will be better off w/ an SA helmet that you wear on your bike. Lots of options available.... try on as many as you can and buy the one that fits your head shape the best. +1 on going as light as possible. It does make a difference.
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Mat P
1988 911 Carrera
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