Posted by Michael Fanoni on Friday, August 25, 2006 at 5:49PM :
In Reply to: LET ME re-OPEN this topic (WC 3/4 ton speeds) posted by dave in Plano, TX on Friday, August 25, 2006 at 1:22PM :
If you know your RPM's and your transmission and axle gearing, then you can very easily arrive at your road speed. Here is a very simple example. 3000 RMP's. -- 7:1 1st gear -- 5.83:1 diff -- 36" tires. Your motor is cranking 3000 revolutions per minute, but your transmission reduces that by a factor of 7. So your output shaft on the transmission is going 428 1/2 RPM's then it enters your diff which reduces it again by 5.83. Now the end of your axel shaft is going 73.5 RPM's. Now if you revolve 73.5 times in a minute then your 36" tires will have carried you 8,309.7 inches. So far so good. Your speed is 8309.7 in/min. Instead of minutes we will use hours, so in an hour we will go 60 times further. Thats 498583 inches per hour. Divide by 12 for feet, then 5280 for miles and we get an astounding 7.87mph. Thats at 7:1 trans ratio. About 1st gear. If you had direct drive (4th gear?), just multiply your MPH by 7. Thats 55mph.
Leave it to the mathematics majors to make a hard problem easy.