Odometer vs GPS

[dennyt]

You can calibrate your odometer on the highway. Note the miles to the tenth at the first highway marker you see. Ten miles later, note the miles and tenths on your odometer. Each tenth over a 10 mile stretch is a 1% error. For example, if you car reads 200,000.0 at milepost 140, and 200,010.2 at milepost 150, it's reading 2% high.

[Weather Spotter]

Originally Posted by Sulfuric

GPS, because every time I turn my engine off with coasting, there is about 1-2 seconds where the ODO does not record any movement. Over a 400 mile tank with heavy P&G I can end up 15 miles off (low) if I trust my ODO instead of GPS.

You need a kill switch, it keeps the dash on while EOC.
Engine kill switch - EcoModder

[BHarvey]

Have not used EOC but neutral coast alot with engine on. Cut the engine at lights if a long one but only during the daylight hours.

[oldbeaver]

Odometer does take in account climbing slopes, while GPS don´t.

The best way may be to calibrate odometer (or mpguino) in a flat surface with GPS, make a conversion table and then trust odometer.

However, if you want to measure only arc flat distances (kind of X, Y coordinates), GPS is correct and you don´t need corrections or conversions.

If you want to consider "real" miles traveled, odometer is correct as it measures on kind of X, Y, Z coordinates. Remember that we move on a sphere surface. Earth is not flat.

As someone said, they measure different distances. If in good shape, both are approximately correct in their own measures.

Oldbeaver

[kamesama980]

I would imagine it depends on the GPS manufacturer as to whether it accounts for the Z axis as well as X and Y. and what it was intended for. Cheap ones probably do not. expensive ones might. ones meant for off-road use as well most likely.

I go by GPS over odometer. Odometer only has to read within X% from the factory. That's going to be averaged across a few similar but not identical tire sizes at a certain pressure, and in my case I run larger tires at higher pressures in all my cars. I correct the Cressida +15% with the winter tires on: 215/65R16 vs 195/65R15. Take that winter mileage :-D

[gone-ot]

..ah, but what *is* the aggregate vertical (Z-axis) error with GPS?

...Answer: a lot more than the latitude and longitudinal X- and Y-axis errors.

...some reading: http://users.erols.com/dlwilson/gpsvert.htm