Last summer I put new radial tires on my car (P215/70R14 Radial T/A). Not surprisingly they are a bit taller than the tires the speedo gear is calibrated for (E70/14). At 50 mph on the speedometer my GPS indicates about 52 mph. I figured the odometer would register low as well but yesterday I tracked a trip with a travel app on my phone. Odometer said I travelled 73.2 miles, the app says 70.7. So the speedometer reads low, odometer high? I'm not smart enough to figure this out.
My speedometer head on my 66 Strato Chief is doing the same thing. The odometer is almost perfect, the speed is off almost 10 mph. I've just learned to live with it but apparently there are places to get the speedo head rebuilt. It has to do with the magnet apparently.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
Thanks and I agree, just live with it. Was a curiosity that the discrepancies are in different directions. Prior to the tire change my speedometer was dead on with the GPS.
I'm not sure how it is where you are but it's easy for us to check our odometers out on the prairies where I am. There's highways that go straight as an arrow for miles with a mile road intersecting the highway every mile. I just go out and drive 3-4 miles and check the odometer. Also I drive 60 on the speedo and time it. Or I used to, now I just use a GPS to check speed.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars