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Old 09-07-2003, 10:58 AM
Duke2.6 Duke2.6 is offline
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Join Date: Mar 2003
Location: Southern California
Posts: 2,011
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.

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