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

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.

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## 10 Replies

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)2009-09-03

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.

steveastrouk (author)2009-09-03

GIve the man a banana !

squirt8500 (author)2009-09-03

43.161512027491408934707903780069 MPH To be exact

steveastrouk (author)2009-09-03

Err ?

squirt8500 (author)2009-09-03
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!!

steveastrouk (author)2009-09-03

5280 Feet in a mile.

bowmaster (author)2009-09-03

Well I was way off. Could you show me how to calculate that?

seandogue (author)2009-09-03

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.

steveastrouk (author)2009-09-03

No.