What's the rpm difference at 130 km/h in ML320 and ML230?     ML320    ML230   A  5th gear 0.830      0.799  B  axle ratio   3.70   4.78   final ratio = AxB  3.071 3.819 Final gear ratio means the tires turn x times less than the engine crank shaft.   Kilometers per minute 2.16666 2.16666 Here are 130 Kilometers per hour converted to x Kilometers per minute  tire size   255/65R16   225/75R16    tire circumfrence in mm   2 251 2268  wheel rpm @ 130 km/h 962.5 955.3 Note that the tire on the ML320 is slightly smaller than the ML230 tire !! Dividing Kilometers per minute by the tire circumfrence gives us the revolutions per minute of the wheel engine rpm  2 956 3 648 Revolutions of the wheel per minute times the final ratio gives us the engine rpm Difference between ML320 and ML230 is 692 rpm @ 130 km/h © 1998-99 Harold Pietschmann