my odometer says 29.5 miles
my gps says ... 28.5 miles...would you ''trust'' the gps better right ???

im going to put some 15inch rims on it prob. on wed after work to see if i can can speedo closer there tires the size of a 91 560 sel.so are taller .

putting a 2.88 speedo head will make it read faster right ? more miles than before ?

The problem is that mileage varies with speed. With small amounts of fuel, slight variations if your fill point effect calculations. Drive a few weeks then calculate mileage if you want an accurate all around figure.

There are tire size calculators that show the effect on speedometer reading of changing tire size.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.