# Is it correct that if an 8-inch diameter wheel was rotating at 1,000 RPM then the vehicle would be going 12 MPH?

I'm making an electric mountain board and I am trying to find what gear ratios work to get the speed I want. I don't know if my math is right and I was just checking.

sort by: active | newest | oldest
8 years ago
Circumference is 25.13 inches, at 1000 rpm that's 2513 inches per minute, is 1,508,000 inches per hour, is 125,500 feet per hour, is 42,000 yards per hour, is 23.8 mph. You might have made an error on the circumference pi*D or 2*pi*R L
bowmaster (author)  lemonie8 years ago
I know what happened. I was doing this at school with one of the crappy school calculators that you have to push the buttons hard to get it to work. I did 8*1.4 instead of 8*3.14.
8 years ago
GIve the man a banana !
squirt85008 years ago
43.161512027491408934707903780069 MPH To be exact
8 years ago
Err ?
8 years ago
wow wait a second i think i was off lets see here

• 2*pi*R //8*3.14= 25.12
• RPMS*25.12 //1000*25.12= 25120
• 60 minutes in a hour sooo... 25120*60= 1507200
• 12 inches in a foot sooo... 1507200/12= 125600
• 5820 feet in a mile (i think) so.... 125600/ 5820= 21.5807...
There we go!!
8 years ago
5280 Feet in a mile.
bowmaster (author)  squirt85008 years ago
Well I was way off. Could you show me how to calculate that?
8 years ago
it's a lesson in unit conversion. how far does an 8 inch wheel go in 1 revolution?> How many seconds in a minute? how many minutes in an hour? How many feet in a mile? basic stuff..you should be able to do.
steveastrouk8 years ago
No.