Larger Diameter Tires - Odometer / Speedometer

As others have said, the odometers and speedometers rarely are both correct. The explanation I got from an engineer who worked for Ford was that they usually were setup for the Speedo to be about 1-2mph faster than actual to help prevent tickets, and the possible lawsuits to pay them. The odometers tend to be a bit closer to actual, but both of the readings will change with tire wear. They have been this way as long as I have been driving back into the sixties in 50's cars.