Larry opined:
At 125 mph, a helmet never saved anyone. It's one of Darwin's laws...(c;

Back when I started riding the DOT rules were to test helmets for a max
of 3mph crash protection. That consisted of dropping a small weight on
it from some specified height and if it didn't crack or deform past a
certain point then it passed and was "DOT certified". Basically that
meant that any helmet made from something stronger than paper mache'
passed. To be effective in any sort of real crash (other than for road
rash) it is the thickness and properties of the padding inside that
determines its protective effectiveness. I talked to a surgeon once who
said that with helmets on in a hard smack the person usually dies from
brain swelling - which he said would be orders of magnitude more painful
and just as deadly as crushing the skull, or, they would die from a
broken neck from the helmet rebounding from the stored energy. Ya pays
yer dues, ya takes yer chances...