The first FIM sanctioned 10Omph motorcycle was Ernie Walker's 994cc Indian in 1920, but the unofficial record is Glenn Curtiss who bolted his V8 aero engine in a motorcycle chassis and did 136mph on January 24th 1907.
Simple eh? That's not quite all though. To maintain accuracy the integrating wheel has, what is in effect a small flywheel mounted below, fixed by a friction spring. This prevents the integrating wheel skipping as it returns to its zero stop, which would result in a false zero - errors which would be cumulative on the next reading.
The stabilizer wheel has two functions. The simpler one is to ensure an accurate zero position of the needle. In the edge of the wheel is a groove, into which a small V shaped spring falls when the needle returns to zero. The more complex function is an averaging device, ensuring that the needle points where it is supposed to -not as straightforward as you might think because with 135 teeth on the edges of the integrator and recorder wheels, for a given speed the final position of the recorder wheel will vary on each cycle depending on the exact point of engagement between the pinion and integrator wheel, and between the recorder wheel and its retaining spring. Careful choice of the size of the hole in the stabilizer, in relation to the size of the driving pin in the recorder wheel, averages these variations out.
The lower cam raises the leaf spring controlling the integrator wheel, allowing it to return to its starting point but leaving the recorder and stabiliser wheels in their new position.
The sequence is constantly repeated with no change so long as the speed remains stable. If the bike slows down, the integrator wheel won't find its original position so on the next cycle, when the recorder wheel isn't released it will fall back to the new position of the integrator wheel. Taking with it the stabiliser wheel and needle.
If the bike goes faster, the deflection of the integrator wheel will be greater and it will therefore pick up the recorder wheel etc, and carry it to its new position. Each sequence takes around half a second which is why a chronometric speedo appears to 'tick' its way around the dial.
After one revolution (0.6 sees on a speedo, slightly less on a tacho).
The counter wheel which has reset to zero point will again push the spindle gear and the new measurement will start. If at this point, the cable's speed is more than the previous measurement, the recording wheel will be pushed even further. If it is less, then the recording wheel does not reach the recording pin and the counter wheel stops turning.
first 100m p h production bike
By the early 20s, speed was big business. At the heart of the Brough SS100 was a 980cc ohv JAP V-twin. In early 1924, Bert Le Vack set a record of 118mph on an SS100 and each bike famously came with a certificate guaranteeing 100mph performance.
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