or was it just a fluke? We travelled from Michigan to Tennessee a few days ago. The Google Maps mileage estimate was 516 miles and our odometer read 516.2 as we parked at the motel. With all the variables involved I'd have to think it was just a coincidence unless the odometer is somehow linked to GPS.

Do you have a Sirius link in the car? Or were you using Car Play/Android Auto or Waze/Maps during the trip? All of these will provide real time GPS data to whoever wants to buy it. Same with the maps/navigation "feature" found in most late-model vehicles' infotainment systems (which is always on whether you want it or not).

They are super accurate by law.

How much slack is allowed in odometer until speedometer is 1mph off?

I think you have it backwards. Odometers have been accurate a long time but it's the GPS that has improved its accuracy. Historically they added unecessary turns, recommended shortcuts that don't exist, has you drive past your street and make a u-turn because it doesn't know there was a left turn, missed lengths of offramps, etc.

A few example:

uber's GPS had a glitch and every time I took an uber to the airport it tried to make the driver pull into one exit of a Citgo gas station and drive out the other exit even though it was located on a straight section of road. In other words, GPS had a longer route for no reason.

a few years ago, I was returning the rental car to FAI (Fairbanks, AK) and my drive originated from an part of town I didn't know. I got close to the airport and was fortunately very familiar with this area. The damn GPS tried to get me to drive into general aviation, across the tarmac, and return the rental. I ignored it and drove the proper route which is longer than the GPS route. A few weeks later a state senator/representative followed the GPS onto the tarmac and had a full scale homeland security response.

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Ego is the anesthesia that deadens the pain of stupidity

DISCLAIMER: These are the author's own personal views and do not represent the views of the author's employer.

There is a little bit of change from the diameters of having full tread and low on thread, but probably less than 1 mph difference at 80 mph.

The vehicle does have a navigation system and Sirius XM.

I think Tatortodd has it correctly diagnosed. The GPS makes a bunch of assumptions about the routing of a trip. Getting off the route to take a leak, getting gas, construction detour, all affect accuracy. My favorite is the ETA, which my wife takes as gospel, well at least as far as her getting herself ready to go is concerned.

I would not be surprised to find all the phone based routing reports back to the mothership at trip end, or even along the route many times to help accuracy.

quote:

Originally posted by konata88:
How much slack is allowed in odometer until speedometer is 1mph off?

I don't know... but on my old VW there was this cable you could unscrew, and then you didn't have either an odometer or a speedometer.
And I can remember cars that had different size tires between the front and the back and that threw it off too.

I've had four BMWs and the Odometers have always been accurate but the speedometers are always reading 2-3mph lower. I've tested with GPS and those police speed signs (we have four at work and I pass two of them coming in to work everyday). I've even tried coding the speed differential thing off and it doesn't work.

The few times I drive my daughter's Subie in, it's accurate. My Alfa is also reading slower than actual speed.

I did a 100 mile test once in my truck on the Interstate.

100 miles by the roadside markers registered within 1 Mile of 100 miles on my odometer.

That was a purely mechanical odometer, and before GPS.



A google:

Electronic vs. Mechanical Odometers – Modern digital odometers tend to be more precise than older mechanical versions, but even they can have minor deviations.
In general, most odometers are accurate within a small margin—often within 1-3% of actual mileage. So, if an odometer shows 100 miles, the true distance might be anywhere from 97 to 103 miles depending on these factors.

Used to drive 400-600 miles a day in various trucks. Ditto the comments on GPS accuracy improving.

quote:

That was a purely mechanical odometer, and before GPS.

So, are odometers no longer mechanical? I guess it gets back to the question suggested by the OP, which has not yet been addressed: are odometers now linked to GPS? AFAIK they are not.

I don't think it would be called an odometer if it were using GPS. An odometer is determining distance traveled by counting wheel rotations and multiplying by tire circumference.

My C5 Corvette odometer works in reverse!

quote:

Originally posted by bdylan:

I don't think it would be called an odometer if it were using GPS. An odometer is determining distance traveled by counting wheel rotations and multiplying by tire circumference.

From the Greek. Hodometros -- an instrument for measuring distance by land or by sea. This definition states what it does (measures distance), but does not state how it achieves the measurement.

I once filed a complaint with the state's dept. on weights and measures because a U-Haul I rented to just move from one storage space to another had some shenanigans with the odometer going on. IIRC, the new space was eight miles from the old one and I made two trips. So call it 32 miles and a maybe another mile out of my way for a u-turn to fill the tank. They said I had gone 55 miles. I hadn't even been gone long enough to drive that far even if I hadn't loaded and unloaded the truck.

When a investigator from the state called me to discuss, he said it was out of their hands, as the truck was now in FL. But he said it was common for those outfits to put much smaller tires on their trucks to make drivers think they were driving faster than they were and that could give a false odometer reading.

quote:

Originally posted by V-Tail:

quote:

Originally posted by bdylan:

I don't think it would be called an odometer if it were using GPS. An odometer is determining distance traveled by counting wheel rotations and multiplying by tire circumference.

From the Greek. Hodometros -- an instrument for measuring distance by land or by sea. This definition states what it does (measures distance), but does not state how it achieves the measurement.

This is true and looking at it closer, Google indicates that manufacturers are integrating GPS with odometers to increase accuracy.. as the OP suggested!