Originally Posted by eddiek
I have a couple of questions. The first is a really basic question, but would there be any significant change in the rolling radius in going from the OEM 19 to the recommended 18" winter tire/wheel combo? 2nd, I have the 19" wheels which I need to get winter tires. There is mostly rain in the Pacific NW but the occasional snow where it is hilly. Are the Michelins that much better than the Blizzaks or Dunlops? Thanks.
OEM 19" and OEM 18" are the same diameter, so this will apply equal to either.
OEM Front Diameter 25.7"
OEM Rear Diameter 26.3"
BMW Alternate winter size 235/40R18 diameter 25.4"
Just for good measure, going up one width front and rear, 255 front and 275 rear with the OE aspect ratio (40 for the 18" and 35 for the 19") makes very slightly taller diameter:
255/40R18 and 255/35R19 are 26" diameter
275/40R18 and 275/35R19 are 26.5" diameter
Keep in mind that like shoes or pants, tires can run a little big or small by a tenth of an inch or two, so these numbers are approximate.