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3-Visitor

## Obtain correct speed in MPH from RPM and tire dia.

I'm currently doing some calcs on the land-speed of a vehicle. From my other calcs, I obtained the wheel-motor's speed in RPMs, and the tire diameter. However, when attempting to obtain the speed from MPH, the calc seems way off. I did it by hand and used an online calculator. and they both gave the correct speed. What am I doing wrong, and how do I get the correct speed calc?

1 ACCEPTED SOLUTION

Accepted Solutions
3-Visitor
(To:PW_10314648)

I was able to figure it out. Here is the calcs for it. The diameter*pi calc in order to get the distance per rev needs to be done separately inside its own variable. I was trying to combine them in the "speed" function. Leaving this here for anyone else who comes across this problem.

3 REPLIES 3
3-Visitor
(To:PW_10314648)

I was able to figure it out. Here is the calcs for it. The diameter*pi calc in order to get the distance per rev needs to be done separately inside its own variable. I was trying to combine them in the "speed" function. Leaving this here for anyone else who comes across this problem.

24-Ruby II
(To:PW_10314648)

Hi,

your problem is related to wrong use of rev unit.

Martin Hanák
23-Emerald I
(To:PW_10314648)

The units "rpm" and "rev/min" have 2*pi radians included, so they refer to angular velocity.  The speed of the tread of the tire is radius times angular velocity, so:

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