[Call Me Bob]

My 2011 750i Xdrive, purchased a year ago with 23,500 miles, has 245 40 19's on all four corners. This is consistent with the "tire size - tire inflation" plaque on the B-pillar however, everything I've researched makes me believe the rears should be 275's on 9.5" wheels. I started looking into this because the rear end would "shimmy" when going over any uneven road surface, including man hole covers.
I'm wondering if anyone else has a similar squared up condition? Is this normal?

Correction; tires are 245 45 19's