Helmet question for track driving

[Perfectlap]

when you put the helmet on have someone try to lift the helmet off your head by holding it from the sides and pulling up. Your neck should stretch as he pulls up on the hard hat. Thats a sign of a good fit.
No neck stretching probably means the helmet is too big or loose. In an impact it could slide off.
Different brands fit different heads in different ways. And the sizes are all different.