I did quite a bit of interstate driving today on I-70. At some point, I decided to try and check and see how accurate the odometer is. I went from mile marker 163 to 77, a distance of 86 miles. The trip odometer only showed 83.8 miles. This means that my odometer mileage needs to be increased by 2.63% to be accurate. I'll check again on my drive home if we stay on the interstate much.

When I filled up earlier today, my calculated fuel economy (gallons put in divided by odometer miles driven) was only 1% lower than the display. We'll see how this trend continues. I don't typically top off, so I can get a bit of tank to tank variance. Anyway, I may start adjusting my miles driven using the calibration factor I measured today.

I have the Goodyear tires and they were at 43 psi cold this morning.

In my Civic, the navi has a diagnostics screen that can show a lot of information. Among the many things it shows are the speed calculated from GPS and also tire calibration. The GPS reads identical to the cars digital speedometer. The tire calibration is set to automatic. I guess this means that it periodically uses the GPS calculated speed to calibrate the tire size.