If you're turning one wheel, with the other one on the ground, the spider gears will cut the driveshaft speed in half. It will take two turns of one rear wheel while counting the driveshaft rotations to get an accurate guesstimate of the ring and pinion ratio.
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!