While I agree smart to wear a helmet at speed, came across this today while researching state law ... if I'm reading this correctly, don't need to wear a helmet in a M3W in CA (USA):
California Vehicle Code 27803 (f) This section does not apply to a person operating, or riding as a passenger in, a fully enclosed (define fully enclosed??) three-wheeled motor vehicle that is not less than seven feet in length (M3W = 10.58 ft long) and not less than four feet in width (M3W = 5.64 ft wide), and has an unladen weight of 900 pounds or more (M3W = 1157 lbs), if the vehicle meets or exceeds all of the requirements of this code, the Federal Motor Vehicle Safety Standards, and the rules and regulations adopted by the United States Department of Transportation and the National Highway Traffic Safety Administration.
This is the new law that Elio got passed in many states so that people don't need a helmet in their fully enclosed vehicle. The M3W is not fully enclosed and therefore unfortunately this won't apply to us.
Well, as "fully enclosed" isn't defined anywhere that I know of, a reasonable view is that if you sit IN it rather than ON it, and it has sides and seat belts, you're OK w/o a helmet. My M3W is at least as fully enclosed as my '55 MG TF...
