Anyone know what helmet specs are for Thunderhill ?
 

I know full face helmets are required, but don't know of the differences after that. I'm trying to figure if I want to buy or borrow one instead of rentin.

It depends on the people who are holding the driving event
 

Most will accept open face helmets also. Usually with a rating of at least M95 or newer and prefer SA95 or newer.

Check with who is holding the events but I would buy your own helmet, better fit and just feels better.

I got mine from Bell Motorsports in Oakland, got the Pyrotect.<ul><li><a href="http://://www.bellmotorsports.com">http://://www.bellmotorsports.com</a</li></ul>

M90 or above minimum
 

If you are going to the quattro club event..there are some available for rental at the event..but you have to reserve them at initial registration.

Are open face OK?

Yep
 

Although I never felt safe in an open faced helmet.

They are letting M helmets go out?

Yep