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Changed Wheels/Tires - Need to recalibrate my Speedo 2000 Expedition

I changed my Expedition’s wheels and tires from stock steel 16" wheels (225/70R16) to the Alloy 17" stock wheels (255/75R17), resulting in about a 5% change in circumference. As a result, my speedo now reads about 5% slower than I’m actually going. I’ve read on the internet that some late 90’s Expy’s can be reprogrammed via OBD. Is this the case with my Expy? Please help before I get a ticket!

Actually your speedometer is likely now reading more accurately than before. Most read about 3-5% slow. The odometer is going to read about 5% off however. Considering it will record fewer miles than actually driven, it might not be so bad.

If you want to correct this I would first see if you have a speedometer in town and start there. If no go there, head for the dealer. I may take some mechanical work or a computer adjustment.

Before going too far, borrow a GPS to confirm the reading on your speedometer against a very accurate measurement(GPS).

Interstate highway mile markers are very accurately spaced. Set your cruise control at 60 miles an hour and see if takes 60 seconds to travel between them. You can also check your odometer at the same time…GPS speed is NOT spot on because the government distorts the civilian signal a little…

Don’t try using the mile markers on Ohio interstates, I think the put them in wherever the get kicked out of the truck, especially in northeastern Ohio.

Already ran the vehicle againsy my GPS (I’m a gadget head). It is, indeed, reading slower than I’m actually travelling. By about 7-8% by my estimate. According to the internet comparison of circumference for my tire profiles (new vs. old) profiles, it should be more like 11%, so I guess that’s the 3-5% you spoke of, Joseph.