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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
BHP measuring
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<blockquote data-quote="Tom Gaynor" data-source="post: 12315" data-attributes="member: 4034"><p><strong>Horsepower at crank vs horsepower at rear wheel</strong></p><p></p><p>The common assumption is that 50 at the rear wheel is 55 at the crank - or at least it is in classic racing circles. Seems a lot in top gear, as has been remarked. However since all I and other racers are only interested in maximising bhp, rather than establishing an absolute number, I don't know of anyone who has investigated the assumption. It wouldn't be terribly easy to do, since all dynos (even of the same basic design) give different results. Stories abound of people seeking the dyno that over-reads most so as to sell their 190 bhp GSX-R for a higher price than a 180 bhp ditto would fetch.</p><p>(In passing, "my" dyno man had never tested anything with "only" 50 bhp at the rear wheel, and we had to develop a technique to get the drum up to speed without burning out the clutch. I had to accelerate the Norton through the gears into 6th. A big Japanese bike just does it in top!) </p><p>I've always assumed that Vincent did enough brake testing to establish that a reasonable Rapide should put out 45, and a reasonable Shadow 55, and those were the numbers attached to all. I expect that in reality Rapides varied either side of 45, and Shadows either side of 55, and that there must have been "good Rapides" and "poor Shadows" that were indistinguishable in performance. </p><p></p><p>Tom</p></blockquote><p></p>
[QUOTE="Tom Gaynor, post: 12315, member: 4034"] [b]Horsepower at crank vs horsepower at rear wheel[/b] The common assumption is that 50 at the rear wheel is 55 at the crank - or at least it is in classic racing circles. Seems a lot in top gear, as has been remarked. However since all I and other racers are only interested in maximising bhp, rather than establishing an absolute number, I don't know of anyone who has investigated the assumption. It wouldn't be terribly easy to do, since all dynos (even of the same basic design) give different results. Stories abound of people seeking the dyno that over-reads most so as to sell their 190 bhp GSX-R for a higher price than a 180 bhp ditto would fetch. (In passing, "my" dyno man had never tested anything with "only" 50 bhp at the rear wheel, and we had to develop a technique to get the drum up to speed without burning out the clutch. I had to accelerate the Norton through the gears into 6th. A big Japanese bike just does it in top!) I've always assumed that Vincent did enough brake testing to establish that a reasonable Rapide should put out 45, and a reasonable Shadow 55, and those were the numbers attached to all. I expect that in reality Rapides varied either side of 45, and Shadows either side of 55, and that there must have been "good Rapides" and "poor Shadows" that were indistinguishable in performance. Tom [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
BHP measuring
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