Speedometer Accuracy vs. Odometer Accuracy

[Jhart]

[cheesy]

there really isn't a good way to calibrate the speedometer.  it works using the dwell (sp?) theory... each GS speedo will vary.. and with age as the spring inside wears out...

Use a gps if you are REALLY that concerned..

[The Buddha]

A car is really within 1 mph of actual ... If its in good and un worn condition ... Yea newish car ... no 1972 ford granada ...
Cool.
Srinath.

[vfrocket]

even if the milage is off, the difference would be neglageble. Changing the oil at the recommended intervals on the odometer would only at best make your oil canges earlier by a 10-10 miles.

that being said, who actually chages it right when the odometer reads another 4000 miles? I dont, so I doubt you are wasting any money.

Oil is the lifeblood of any machine, and changing it regualrly is necesary for the longevity of the machine, and thus is a wise investment.

[mjm]

The various regulatory agencies in the US care greatly about the accuracy of the odometer - but are only concerned that the speedometer not read low.

Speedometers on our bikes are basically two magnetic discs separated by a small space.  The top disc has a coiled spring of the "hairspring" variety that pushes towards the "zero".  As the bottom disk, attached to the speedometer cable turns, it applys a force to the top disk and the needle attached to the top of the top disk moves across the face of the speedometer to tell you your speed.  The magnetic coupling involves a lot of slip, the magnets are not completely consistent, the spring has variation too.  Suzuki throws a fudge factor (rather than investing in higher quality control) into the design just making sure it will not read low.

The odometer is geared to the end of the speedometer cable and there are strict federal and state rules on how accurate they have to be - if they are wrong, then the mileage statements required by law when they are sold are wrong and that would make them very cranky.  They are, by design, very close - but not exact.

You say that your mileage varies over an identical route.  It might be because you do not actually follow the same route.  Were you in the inside or the outside lane on the on-ramp?  Did you weave through traffic or just sit in one lane the whole time?  I can have almost half a mile difference on my four mile commute to work with all five of my vehicles - funny though, the differences seem to have a lot to do with the factors above and work out about the same with all of them.