[ChevyBoiler]

I know this has been discussed in some other threads, but I have some actual data now that I have put my winter tires on, and the results are not what I hoped for.

I have a 2LT RS that came with the 20" rims and Pirellis. I replaced those with 18" rims and 225/60R18 Goodyear UltraGrips for the winter. This combination should have the same Outer Diameter as the 20" rims with 245/45R20 tires, so I would have expected the odometer/speedometer to not be afftected. I took it for a test drive the other day and found that my odometer calibration is incorrect. Using the milemarkers on the interstate, found that I am registering 5.0 miles traveled by the time I reach 4.7 miles by the milemarkers, so my odometer is now gaining a little over 0.3 miles for every 5.0 miles I travel. This is likely throwing off my speedometer as well, but I haven't been able to test that (can't wait to use that excuse when I get pulled over).

Anyway, just wondering if anyone else is finding similar results and what the possible solutions may be?