Its all about freedom of choice in states where the helmet laws allow it.
Around here it seems that (from observation) 98% of the sportbike riders are wearing lids. At times you see them with full coverage lids and short pants in the summer.
Cruiser riders for whatever reason seem to statistically (once again based on my observance) are more likely to not be wearing a lid.
I dont make judgements as to any of this cause I believe in freedom of choice as long as the law allows it.
I do think the crotch-rocket crowd chooses a helmet more so cause the bikes bascally look exactly like road racers....so they WANT to look like racers and this implies a helmet by definition.
Cruiser bikes are more laid back and so are the riders to some degree.
But thats just my opinion and I could be wrong
