Here's another from back in the 80's.
I used to have one of those Sanyo speedometers on my racer that ran off a cable connected to a small wheel on a spring loaded bracket that ran against the front tyre (similar idea to a dynamo). The speedo went up to 50mph, although looking back I somehow doubt it was entirely accurate.
The trouble was at anything above an indicated 25mph, the little wheel had a tendency to skip and jump about, meaning the needle never gave a steady reading.
So I decided to cycle down the steepest local hill, which just happened to be a dual carriageway, pedalling as quickly as I could in the highest of my 12-speeds with one hand on the drops, the hand other reaching down the front fork holding the small wheel in place against the tyre, while looking at the speedo rather than the road ahead...
I'm pleased to report that somehow I survived unscathed and, perhaps more importantly, managed to get the speedo needle off the clock.
