So, I just went thru all 115+ posts regarding the helmets.
I speak from experience. I was in a major crash in my 1st SS. That's it to the left in my Avatar. Ford Mustang turned left directly in front of me and I t-boned him at 55+ MPH. I tried to turn hard left but all that did was turn the SS left slightly while still moving into a straight line. SS went into his passenger side front tire, UNDER the door, and PEELED the sheet metal from the side of the Mustang. SS spun around clockwise a few times and I came to rest 3 lanes away. Turns out (during the legal dispositions) that I was knocked unconscious for a few seconds - enough time for the other driver to get out of his car and come over towards me. You can read about it on TDS in the Batmobile is Totaled thread.
I was wearing the stock 3 point seat belt and no helmet. Yes, there was flying debris everywhere - windshield shattered and just added to the shrapnel. My eyeglasses were destroyed. 3 yrs later I still have to use a pillow to support my right shoulder while sleeping.
Point of all this: I am ABSOLUTELY convinced that NOT wearing a helmet in the SS SAVED MY LIFE. Remember about being unconscious - I'm sure that the extra weight of ANY helmet would have snapped my neck.
You see, motorcycle helmets are meant to protect your head when your body is flopping around after a motorcycle crash. Your body is not restrained by seat belts so the expectation is that you are separated from the MC and the helmet is there just to protect that fifth appendage from hitting hard things.
In any vehicle where your body is restrained by seat belts you're no longer going to be separated from the vehicle. Thus it's the vehicle itself that becomes the protection for your appendages. And those need to be secured from moving around. Adding extra weight just makes it harder for that vehicle to protect it's passenger. Would you strap extra weights to your arms and legs and think that would help in a crash?
So if you're wearing a helmet in a seated vehicle where you are secured, you need that helmet to be secured to that vehicle with any sort of HANS device. Ask Dale Earnhardt Sr. about his helmet in the car without wearing a HANS. An unsecured helmet in a secured vehicle is a dangerous combination.
That also being said, the 3 point seat belts did as much damage to my body as anything (okay, maybe not as much damage as the steering wheel, but you get my meaning). The 3 points in a vehicle without crumple zones and airbags is just the minimum LEGAL requirements. I have switched to 4 points in my SS (yes, I mounted them correctly), but am looking to even upgrade those to H-Harnesses. I thought I would check with other people in the Ozarks about their recommendations.
To add to my justifications, I've ridden motorcycles and dirt bikes for 30+ years and ALWAYS wore a helmet, even if I didn't wear other protective gear (jacket, boots, etc.). I agree with wearing helmets. I'm just saying that wearing a helmet INCORRECTLY is worse than not wearing one at all.