Posted by **Alex** on Tuesday, March 30, 2010 at 8:31pm.

The radius of each wheel of a car is 16 inches. At how many revolutions per minute should a spin balancer be set to balance the tires at a speed of 90 miles per hour? What is the setting for a wheel of radius 14 inches?

- math -
**noel**, Tuesday, March 30, 2010 at 10:14pm
base figures you need to know

5280 feet in a mile

12 inches in a foot

60 minutes in an hour

The circumference of a circle formula is circumference = pi * radius * 2

the trick of this problem is you have feet in the mile but inches in the tire & hours in the speed but minutes in the revolutions

so you would have your speed (90) miles per hour divided by (60) minutes times the number of feet in a mile (5280) times number of inches in a foot (12) divided by the circumference of the tire pi * r2 (3.141593 * 16 * 2)

- math -
**Alex**, Wednesday, March 31, 2010 at 4:37pm
what happens to the 16 inches and 14 inches.

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