OT - Faulty odometer reading - 05 Buick

oem tires? perhaps they're the wrong size than the odometer was calibrated for.

Different tires than stock?

Nick

For the odometer to read more miles, that would mean smaller tires, not bigger don't ya think?

In my neck of the woods, there are places on the interstate that have odometer milage signs for checking your odometer. Seen any where you live?

Lane

Another idea is to find a reputable speedometer shop and ask them if they've seen problems with cars similar to yours.

Lane

Realize that the difference between 1245 and 1321 is only 6%.

What is the accuracy rating of the spedometer? Yours may be running on the high side.

You can calibrate it by comparing its reading with the milepost spacing on Interstate highways.

Harry C.

Ah ha !! Now I know how they get the better "gas mileage numbers" on the new cars !! Check the odometer yourself -- most of the freeways have the mile markers on a small post along the side of the road (and most have finally figured out how to use that for the exit number which makes sense). Anyway, do 20 or 30 miles down the freeway and note how your numbers compare to the freeway markers. (you can also check the speed easily at

mikey

PLUS.... your mileage warranty runs out sooner..... Ken.

They put the big-tire speedometer cable drive gear in the trans, and small tires on the car. The dealer parts counter can sell you a replacement drive gear for the transmission with one or two more (or less) teeth, which will correct the error. (Or at least get it a whole lot closer.)

Or a good speedometer shop can sell you a little gearbox that goes inline behind the speedometer head, and drops the cable speed going to the speedometer by whatever gear ratio you need to get as close to dead on as possible - someone said 6% for your car.

They are made for people running road rallies, where having the odometer dead-nuts accurate is very important.

And then you change tire brands or change the tire size slightly (and the running road-contact OD of the tires) and knock the calibration off again.

-->--

I made my own measured mile by driving another car with a good speedo along a local road, and noting the location of 2 landmarks. Then I drove the car in need of calibration alond the measured mile and noted any differences.

Tony

I started thinking maybe low tire pressure and a smaller rolling radius. And then my brain kicked in and realized it's the circumferance of the tire that matters, and with belted radials that won't change much at all with tire pressure, will it, or am I "smoking the drapes" again with that?

Interesting to hear that a dealer can recalibrate the car's computer to correct things like that. I wonder if there are two separate corrections, one for indicated speed and another for milage.

I've noticed that my GM car doesn't know whether it's going forwards or backwards. Moving in reverse still makes the odometer increase and the speedometer inticate a positive speed number.

That kind of calibratable odometer would have been nice to have back in the early '60s when the first SWMBO and I went sports car rallying nearly every Sunday for several years. We had to calculate and incorporate a "correction factor" to match our odometer to that of the "Rallymaster" who set up the event, by driving over a their measured distance at the start of each rally.

I still have the Curta calculator we used for those rallies, and (metal content here) the motorized drive I built to crank it through it's bottom. It snapped around one full turn each time a microswitch geared down from the speedometer cable clicked off another hundredth of a mile.

Thanks for the mammaries, and don't laff at the '55 Chrysler in the photo link below. Superior technology helped us beat out the teams in the real "sporty cars".

She drove?

Do you have a GPS or a friend with one? If so, take a drive with one (after it gets locked in) preferably on a not too twisty stretch of road. On a decent day you can expect accuracy of a few yards over virtually any distance. For the very best accuracy, get a (free) copy of G7toWin from

BTW, you can easily check the spedometer as well.

Ted

Like Juan-Manuel Fangio she did...

Not to brag, but we were SCCA Northeast region rally champs for two years running..

Jeff

Women can better drive than read maps.

Ni-SCNR-ck

So now you have two sources of error. How do REALLY know your benchmark car has an accurate speedo? It could be reading a couple percent off in one direction and the other car a couple percent in the other direction and you really don't have a problem at all. You need to use a known standard. ie Mile marker signs on the expressway or borrow a GPS.

I immediately thought the same thing but on a reread of the post I think he said he essentially got the same mileage with four vehicles. (Probably the odd man is out.)

He is reporting about 6% error. I have checked car speedometers with a GPS and finding them 2-3 MPH off at 50-60MPH is very common. (and about the same error). It would be interesting to know the tolerance on car odometers, but I suspect it not much better than that.

So I still don't think comparing the odometer readings is very useful because you really need a known standard to calibate something.

The only way to do this right is to compare the obometer to a known standard such as milemaker signs or a GPS.