I never wore a bicycle helmet until a car stopped in the bike lane to make a right turn. The lady was waving me around her as she sat there. This was after passing me and swerving in there. That was in California, and motivated me to wear a helmet on my road bike. I din't have a motorcycle, and I'm not really sure the same applies. I ride around my dead-end street gearless to test my bike after a mod or tune-up, but the last 400 feet of it belong to me, so I can clearly see the traffic situation, as the whole street is only 1/4 mile long.
Still, I don't know what I'd wear out here if there wasn't so much sand on the road all the time. We spend a bit of time in out-of- shape riding configurations on some of these roads. There are heaved up bumps in the middle of many of the curves, too. It's not uncommon to skip a little, even on dry pavement when you hit one of those at higher speeds. On my bike, a half helmet would probably look funny anyway.
I did see a local bike mechanic test-riding a customers R1 with his chrome party helmet on, though. Now that was funny!
