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Vincents - A New Interest For Me
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<blockquote data-quote="Tom Gaynor" data-source="post: 8504" data-attributes="member: 4034"><p><strong>Speedometers</strong></p><p></p><p>By calculation (according to Paul Richardson), the speedometer should be 1.8% fast with 3.00 x 21 (Lightning) tyres. The distance part of the speed calculation is based on 1600 cable revolutions per mile. (Smiths also made instruments at 1450 and 1700, 1600 is most common). In a perfect world the ratio would be higher (about 1680) for 3.00 x 20 and 3.50 x 19 tyres which apparently have almost exactly the same rolling circumference. FWIW, checking mine against GPS, 3.00 x 20 tyre, 100 mph Speedo was 97 mph GPS, which ought to be the error in the odometer (because it is the distance ratio that is fundamentally wrong), and it is.</p></blockquote><p></p>
[QUOTE="Tom Gaynor, post: 8504, member: 4034"] [b]Speedometers[/b] By calculation (according to Paul Richardson), the speedometer should be 1.8% fast with 3.00 x 21 (Lightning) tyres. The distance part of the speed calculation is based on 1600 cable revolutions per mile. (Smiths also made instruments at 1450 and 1700, 1600 is most common). In a perfect world the ratio would be higher (about 1680) for 3.00 x 20 and 3.50 x 19 tyres which apparently have almost exactly the same rolling circumference. FWIW, checking mine against GPS, 3.00 x 20 tyre, 100 mph Speedo was 97 mph GPS, which ought to be the error in the odometer (because it is the distance ratio that is fundamentally wrong), and it is. [/QUOTE]
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