That's basically the way it's done.Be sure to only jack up one wheel.I usually use yellow tire crayon and mark a place I can see on the backing plate and the rim at the same place,then mark the pinion yoke and axle housing in the same manner.then just rotate the wheel slowly and count the revolutions of the drivelineto make one full revolution of the wheel.If the driveline finishes on a partial turn,try to round it off to the nearest 1/8th turn,for accuracy. That'll give you your gear ratio.
http://www.angelfire.com/fl4/pontiacdude428/Hot.html http://www.onlineconversion.com/bigger_tires.html These are a couple of good nomber crunchers to figure out how tire sizes or gear ratio changes will affect your road speed,as well as other things you've always wondered how to figure out.
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