As others have said it's measured at the transmission not at the wheels. When it comes to changes due to wheel diameters only the rear tire diameters matter because they're the drive wheels.
GONE: '08 335i Coupe, Space Gray, Coral Red, Gray Poplar, 6-MT, ZSP, ZPP, ZCW, 19" Style 230 Wheels, Nav, CA, PDS, Sat, HD, IPod. ED 10 May '08.
NEW ARRIVAL: '11 M3 Convertible, Mineral White, Fox Red, Extended Leather, Carbon Leather, 6-MT, 19" Style 220M Wheels, EDC, EPS, ZP2, ZCV, ZCW. ED 29 Apr '11