Some years ago, I had a friend´s Comet for some time. It was an original "C"-Comet. When it topped at 75mph, I asked a friend, to follow in his car and tell me his speedo readings afterwards. He confirmed my
readings, stating, that his Moto Guzzi Falcone did the same speed with a sidecar on!
So, I remembered, that this speed was also achieved by my first motorcycle, a 1952 NSU Max, 250cc, 18hp.
And I decided, to find out why.
Next step was, to fit a bicycle speedo, carefully adjusted. The Comet´s engine was in good trim, everything
well tuned, nice plug face, etc. So I started on a sunny afternoon on a flat, free motorway nearby and revved it
in 1st, until it did not accelerate, anymore, remembering the speed, the same in second and third. In fourth,
it topped at 75 with me sitting up. I stopped and noted the figures on a sheet of paper and went back home.
With the figures from Paul Richardsons book, I calculated the engine speeds in each gear and found out, that,
with works sprockets, it stayed 1000rpm below max. in fourth gear, which is app. 17 - 18 hp at the rear wheel.
So I fitted a 52 teeth sprocket, which was 4 teeth over standard.
Same day, same road, same conditions, and it achieved 90 mph, exactly works figures!
I do not torture my bikes, but they must deliver works standards!