Vincents - A New Interest For Me
- Thread starter syclone
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The speedo is mounted thus, to remind you, that when you brake hard, it actually comes towards your face, to let you know you`re playing `silly ******s`. In other words `Take note`.
Unless you are Rapcom , who assures me his one gets further away ! Over to you Dick
John
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Movement of speedo (or not)
John, I've never said it gets further away, just that I notice the bike going UP when I brake hard. Presumably the bit I notice, the steering damper knob, is rotating along an arc centred on the forward spindle of the top link, which is where the speedo is mounted, but whether the distance between the riders eye and the speedo actually decreases would require some good maths to work out.
Then of course it would depend on the height and build of the rider, and whether he slid forward under the influence of the heavy braking. Perhaps the coefficient of friction of the seat cover would need to be accounted for?
I think I'll go and lie down now.....
John, I've never said it gets further away, just that I notice the bike going UP when I brake hard. Presumably the bit I notice, the steering damper knob, is rotating along an arc centred on the forward spindle of the top link, which is where the speedo is mounted, but whether the distance between the riders eye and the speedo actually decreases would require some good maths to work out.
Then of course it would depend on the height and build of the rider, and whether he slid forward under the influence of the heavy braking. Perhaps the coefficient of friction of the seat cover would need to be accounted for?
I think I'll go and lie down now.....
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Speedometers
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.
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.
....what- no mention of changing speedo drive ratios?
Not having any MPH's prior to 12/08 at my disposal to confirm this notion has likely been flogged on more that one occassion over the years when this discussion's come up, surprised noone has debated the possible influence of the dwindling size of the wearing fibre drive gear against it's steel mate within the front drum as changing the drive ratio.
Not having any MPH's prior to 12/08 at my disposal to confirm this notion has likely been flogged on more that one occassion over the years when this discussion's come up, surprised noone has debated the possible influence of the dwindling size of the wearing fibre drive gear against it's steel mate within the front drum as changing the drive ratio.
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Speedometer readings
Just to add another angle to the debate, my outfit has 13" wheels, so the clock is reading somewhat fast.
I do not know what % error is involved but here's the interesting bit, my rev counter gearbox is in the ratio of 1to1, not as it should be at 2to1, but would you belive it, in top gear, the rev counter equates almost spot-on with miles per hour.
As an example, the revcounter shows say 4000, i.e. 40 mph, but the speedometeris reading is 55+. The up-side is, that if I ride to the speedo, I'll never get a ticket for speeding.
When I first put the outfit back on the road, I did make a sticker to fit on the speedometer, which was pretty succesfull, but don't feel the need for it currently. Thought it might be of interest.
mr.hutch
Just to add another angle to the debate, my outfit has 13" wheels, so the clock is reading somewhat fast.
I do not know what % error is involved but here's the interesting bit, my rev counter gearbox is in the ratio of 1to1, not as it should be at 2to1, but would you belive it, in top gear, the rev counter equates almost spot-on with miles per hour.
As an example, the revcounter shows say 4000, i.e. 40 mph, but the speedometeris reading is 55+. The up-side is, that if I ride to the speedo, I'll never get a ticket for speeding.
When I first put the outfit back on the road, I did make a sticker to fit on the speedometer, which was pretty succesfull, but don't feel the need for it currently. Thought it might be of interest.
mr.hutch