wow, smokin' deal!
i also run the 215/55/17 for winter right now. plan to switch to 235/45/18 for summer.
same as Fix_Until_Broke - my speedo now reads accurate with no calibration for tire size change. i left it alone with VCDS. the speedo needle is a hair fast, but the cruise setting speedo is 100% accurate, conffirmed many times/many miles with both Garmin GPS, and smartphone GPS/mapping. however, my odometer is now 3% behind. i'm fine with that, i just compensate for that number when calculating fuel mileage.
don't ask me how the odometer is only 3% behind with a 5.2% larger diameter tire! again, this has been confirmed with separate GPS units many times.