Question 371997
"I own a 2006 Honda CRV. Last spring, I was still driving on the original tires. I looked at them and decided that I had worn down enough tread, so it was time to buy a whole new set of tires. Let us say that I began with 16-inch tires (11/16 inch of tire tread depth). If I drove at 60mph, how many revolutions per hour would one new tire make? Let us say that I drove 40,000 miles on those tires so that the tread depth wore down to 3/16 inch. If I drove at 60mph, how many revolutions per hour would one worn tire make? Calculate the difference in revolutions per hour between the new tire and the worn tire."


circumference = diameter * pi
circumference new tire = 16 inches * pi = 16pi inches
11/16 inch tire tread depth - 3/16 inch tire tread depth = 8/16 inch tire tread depth
8/16 inch = 1/2 inch --> diameter old tire = 15.5 inches
circumference old tire = 15.5pi inches
60 mph = 60 miles in 1 hour
new = 60 miles * 5280 ft/mile * 12 inches/ft * 1/16pi rev/inches
new = 3801600/16pi revolutions
new = 75630.428957 rounded to 6 places revolutions in 60 miles
old = 60 * 5280 * 12 * 1/15.5pi revolutions
old = 3801600/15.5pi revolutions
old = 78070.120214 rounded to 6 places revolutions in 60 miles
new - old = 75630.428957 - 78070.120214 = -2439.691257 revolutions
75630 - 78070 = -2440 revolutions
old tires make 2440 revolutions more in 60 miles at 60 mph


if i made a mistake, someone let me know, and i apologize if i did