With one wheel jacked up and the transmission in neutral, the driveshaft will turn twice as fast as normal when you turn the wheel. The spider and axle gears double the ring & pinion ratio. A more accurate way to check R&P ratio is to mark a spot on the tire, roll the vehicle straight forward exactly one turn of the wheel, and count the turns of the driveshaft. A 3.90:1 gearset will result in almost 4 turns of the driveshaft doing it that way.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!