Calc rear axle ratio

[Craig M]

I have used the old trick of jacking up one side of a vehicle, rotating the tire one revolution, and counting the revolutions of the driveshaft. This has worked a couple of times. Have tried it twice recently and results have seemed to be half of what would be expected. 2.25 revolutions (when expecting 4.53 or so). Am I missing something?

[DmaxMaverick]

That sounds right for the one side method. The differential gear will allow one wheel to turn at 2 times what both will turn at, which will cause the shaft to turn at 1/2 of the gear ratio. If you are expecting a 4.53 ratio, then 2.25 turns on the shaft would be correct.