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In rear-wheel drive automobiles the central drive shaft (or prop shaft) engages the differential through a hypoid gear(ring and pinion). The ring gear is mounted on the carrier of the planetary chain that forms the differential. This hypoid gear is a bevel gear that changes the direction of the drive rotation.
Calculating Ring & Pinion Gear ratio. The easiest way to determine your ring & pinion gear ratio (sometimes called axle ratio) is to check the tag that's bolted to the front differential cover. On the tag you should see some numbering such as 3.07, 3.73 or 4.11. Any of these numbers are common for a Jeep stock axle ratio. If you want to double check (perhaps a previous owner regeared, wrong factory tag, etc), here's what to do: Jack up the rear axle and support it with jack stands.