Looks like the answer, all right.

Maybe someone can help me with Mechanical Speedometer 101:

1. How do they work?

2. What can shift or age internally to cause them to read higher than
manufacturing tolerance sez they should when used with the correct tires?

I assume that the tires are the correct size (185/14) because the
odometer reads pretty darn accurately (2.5% error). I have a second
reason to make this assumption. I base it on another assumption, a quick
measurement, and some rough math: The little calibration number on the
face of the speedo is 805. I assume that this means that it is set up
for a tire that rotates 805 times in one mile. (A mile has 63,360
inches, the diameter of my tires are (roughly) 25 inches, one rotation
of the tire covers (roughly) 78.5 inches, if it rotated 805 times it
would cover (roughly) 63,192 inches . . . coincidence? You be the judge!)

-- That Rocket J Squirrel guy

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