With one wheel on the ground, the spider gears double the gear ratio of the ring & pinion. 1/2 turn of the rear wheel will yield the proper number of turns of the pinion gear (driveshaft), or make one full turn with the rear wheel, and divide the driveshaft turns by 2. Try it sometime! That's why we had to watch the speedometer very closely when doing an on-the-car spin balance with one rear wheel on the ground- - - - -30 MPH on the speedometer had the raised wheel doing 60 MPH!
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!