When I bought my sd, it had chrome rims. I changed to the flat later 80's style cuz they make the car look more "put together" in my opinion. The speedometer and odometer were VERY off with the 16in chromes. My tire guy got slightly low profile tires so that my new 15s would give the same info as the old 14s. Now my GPS and my speedo and odo are as close to flawless as my calculations can tell. Spot on.

Are you sure that your odo/speedo isn't off due to the profile of the tire?

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg