My bike helmet has a clip-on plastic sun visor at the front that is no more. I'm not sure if it was added by the manufacturer as a means of keeping the sun out of your eyes, or simply to improve the lines of the helmet (ie, a fashion accessory). Whatever its purpose, I left it in place when I bought the helmet.
It's always been a bit wobbly - it's just a bit of plastic with lugs that bed into the foam liner of the helmet, and foam can easily stretch and deform. At normal riding speeds, it wasn't a problem, but I wasn't doing normal speeds last week.
In any given week, I rarely exceed 60km/h - the hills around here just aren't steep enough for a really rapid descent. But I went for a ride into new and uncharted territory, and found a hill that was an absolute ripper - by that, I mean that riding to the top of it almost resulted in me coughing my lungs out of my nose. It was steep and nasty and seemed to go on forever. Hard going up means fun going down.
The speedo quickly went up past 65, so I tucked down into my most aerodynamic position (it's hard tucking right over when you have 20 years of beer drinking wrapped around your waist) and the speedo started heading towards 70 when - WHAP - the visor detached from its middle mounting point and whacked into my sunglasses. I suddenly found myself going very fast down a completely foreign hill with no idea where I was going.
I lost my aerodynamic tuck as I wrestled with the recalcitrant visor, and later found that I had only reached 69.9km/h - which was about when the visor cut loose. I had no desire to climb the hill to try for another land speed record, so exceeding the speed limit by a large fraction will have to wait for another day.
I do wonder though whether a Police radar gun is able to pick up a speeding bike, particularly when they are so full of carbon fibre and other exotic creations. I only ask since I was not in a 70 zone - it's not often that one gets to exceed the speed limit when relying solely on your legs.