I thought I put this to rest last week but after a 200 mile drive I've got it straight in my head (I think).

Using my Garmin iQueM5 finally on a trip I found that in 198 miles (by GPS reading) of driving my odometer read 195.1.

Also driving at 70 miles per hour (by my speedometer) my Garmin was reading in the range of 68.5 miles per hour.

That's why I think I confused myself last week. The errors are divergent.

The Speedometer reads too HIGH. To solve the speedometer error you would have to have a taller tire/wheel combo which would register a slower speed than the OEM's at the same speed, since it takes less rotations of the tire to correct the "too fast" speedometer reading.

However, since the odometer reads LOW you would need a shorter tire/wheel combo to increase the number of rotations per mile over the OEM's to correct the error.

The speedo error is reasonable and it keeps you under the speed limit and is a decently close margin of error. However the odometer error is factored into the FE readings and thus we probably are off by 1.5% (too high) on actual FE calculations. (Still it's pretty close too_not as bad as 5% as some have guessed at)

All in all both were pretty close. But a simple tire/wheel change can't solve both problems since the errors diverge as you make changes.

No responces necessary as I wore most of you out last week on this. I'm just clearing my head.