I changed to a set of Nokian winter tires a couple months ago from a completely-done set of OEM Turanzas on my 08 Touring. Both are stock size and inflated properly while cold (air temperature/volume is not to blame). I had noticed that there was a 1mph discrepancy (to a GPS) with the old, totally worn out tires which I attributed to decreased diameter from tire wear. Now that I have replaced the tires, this has increased to 2-3mph. The difference has been observed to be as high as 4mph. Given that the car is often travelling at speeds where this effect is seen, I'm a concerned about the cumulative effect on the odometer. Is there any verifiable evidence that the odometer isn't diverging from the real mileage? In the end it probably won't matter since I fit 205/55/16s during the summer. EDIT: I have Nokian Hakkapeliitta snow tires, not any sort of WR. I have dedicated rims for winter and summer.
Interesting... I haven't checked my speedo against the GPS with the WRs. I do recall it being spot on with the Integritys. It shouldn't be too big of a deal esp. if the Nokians that you have are very very close in revs to the old Turanzas.
