Revs at any speed =

tire revs/mi x trans ratio x axle ratio x (xx/60)

where xx is the specific speed.

The 195/65VR-15 Michelin MXV OE tires are speced at 837 revs/mi; 185/65s on W201s are 849 revs/mile. The above relationship will hold regardless of installed tire revs/mi. If installed tire revs/mi are different than OE, speedometer accuracy will be effected, but the speed/rev relationship does not channge.

The above relationship may be rearranged to solve for axle ratio if you know the OE tire's revs per mile and have a good value for revs at any speed.

For top gear the transmission ratio is 1:1 for automatics and 0.80:1 for M103 five-speeds.

Duke