To find actual miles vs odo miles, I look for mile markers on the side of the highway.
They aren't extremely accurate, but they are accurate enough if you are careful, and you go enough miles.
They'll be accurate to at least a tenth of a mile, and if you go at least ten miles, it will average out close enough for what we need.
It won't matter whether you speed up, slow down, etc. (For the neophytes.) So you could actually pull over at each marker, if you wish, and if you don't think you can 'guess close enough' about what your meter says at the instant you are beside the marker. Just don't back up.
Use the trip meter. Hit the button to zero the meter, when you are exactly beside the beginning marker. If you think you hit it too soon, or too late, start again at the next marker.
When you pass a mile marker, make note of the number that is on the meter. Don't push the button or zero the meter again. Let it continue.
If you miss a marker, no biggie, just keep a better eye out for the next one.
You should have made a note of the number on the first marker. And make note of the differences, if there are any, at each marker from that point on.
Once you have gone at least ten miles, you should be able to come up with a pretty close guesstimate of how many miles you actually travelled, versus how many miles the odo claims you traveled.
If I change to a new tire size, I will do this at least three times, in different conditions, and use the best average of the three questimates.
1988 Trooper LS. 4ZE1. mua5.
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