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From: Salad Dodger on 22 Jul 2010 14:39 How do they work, exactly? I know the wheel goes round, and it drives a worm thing which makes a cable go round which makes a needle sweep majestically across the face of one's speedo, but ... Is the rate of spin of the cable the same on all (most) bikes at the same road speed? i.e. is all the conversion done in the hub drive? -- SD
From: wessie on 22 Jul 2010 15:41 Salad Dodger <salad.dodger(a)idnet.com> wrote in news:lt3h46lthi7d64s7sbvdeqqtqkk5462eam(a)4ax.com: > How do they work, exactly? > > I know the wheel goes round, and it drives a worm thing which makes a > cable go round which makes a needle sweep majestically across the face > of one's speedo, but ... > > Is the rate of spin of the cable the same on all (most) bikes at the > same road speed? > > i.e. is all the conversion done in the hub drive? I know I can make my speedo more accurate by changing the gearbox thing in the wheel hub. Apparently the one from the RT model is better at maths than the one on the R-GS. This suggests BMW speedos are generic items and that any adjustment for wheel size is done by altering the gear ratio in the wheel hub. I bet other manufacturers follow the same principle.
From: The Older Gentleman on 22 Jul 2010 16:14 Salad Dodger <salad.dodger(a)idnet.com> wrote: > How do they work, exactly? > > I know the wheel goes round, and it drives a worm thing which makes a > cable go round which makes a needle sweep majestically across the face > of one's speedo, but ... > > Is the rate of spin of the cable the same on all (most) bikes at the > same road speed? > > i.e. is all the conversion done in the hub drive? Not necessarily. What happens is that in the speedo, the twiddling cable generates a magnetic field which pulls the speedo needle round the dial. So I imagine you could recalibrate a speedo either by changing the gearing (ie: at the wheel end) or by generating a weaker or stronger magnetic field (at the instrument end). The rate of spin won't necessarily be the same, either, because obviously a larger diameter wheel will rotate slower for a given road speed than a smaller diameter one. There again, wibbleflip etc. -- BMW K1100LT Ducati 750SS Triumph Street Triple Honda CB400F Suzuki TS250 Suzuki GN250 chateaudotmurrayatidnetdotcom Nothing damages a machine more than an ignoramus with a manual, a can-do attitude and a set of cheap tools
From: Mark Olson on 22 Jul 2010 16:24 The Older Gentleman wrote: > Salad Dodger <salad.dodger(a)idnet.com> wrote: > >> How do they work, exactly? >> >> I know the wheel goes round, and it drives a worm thing which makes a >> cable go round which makes a needle sweep majestically across the face >> of one's speedo, but ... >> >> Is the rate of spin of the cable the same on all (most) bikes at the >> same road speed? >> >> i.e. is all the conversion done in the hub drive? > > Not necessarily. What happens is that in the speedo, the twiddling cable > generates a magnetic field which pulls the speedo needle round the dial. > > So I imagine you could recalibrate a speedo either by changing the > gearing (ie: at the wheel end) or by generating a weaker or stronger > magnetic field (at the instrument end). > > The rate of spin won't necessarily be the same, either, because > obviously a larger diameter wheel will rotate slower for a given road > speed than a smaller diameter one. > > There again, wibbleflip etc. As far as the speedometer needle goes, you are right, but the odometer/ trip meter is controlled strictly by gearing and cannot be adjusted by fiddling with the magnetic bits or the spiral return spring.
From: The Older Gentleman on 22 Jul 2010 16:26
wessie <putmynamehere(a)tesco.net> wrote: > This suggests BMW speedos are generic items and that any adjustment for > wheel size is done by altering the gear ratio in the wheel hub. I bet other > manufacturers follow the same principle. Yebbut, BMW do seem to have more commonality of instruments than most manufacturers. -- BMW K1100LT Ducati 750SS Triumph Street Triple Honda CB400F Suzuki TS250 Suzuki GN250 chateaudotmurrayatidnetdotcom Nothing damages a machine more than an ignoramus with a manual, a can-do attitude and a set of cheap tools |