Try again, guys! The differential gearing doubles wheel speed, if only one wheel is turning. The gear ratio needs to be figured with 1/2 turn of a rear wheel, if you've only got one wheel free to turn. That's why it's so easy to overheat a tire if it's spinning on a slick spot. 30 MPH on the speedo, for instance, is 60 at the wheel that's spinning.
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!