Suppose you know that tires on the rear of your car will wear out after 21000 miles, while tires on the front of your car last for 29000 miles. Suppose you have a new car and five identical new tires (four installed and one spare.) What is the maximum distance you can drive, assuming you can easily change the tires any time you want?
Each mile you drive uses up 2/29000 + 2/21000 = 1/6090 of your tires. Since you have 5 tires, 5*6090 = 30450 miles.
Since there are no limitations on tire rotations, there is no reason why this limit can't be reached. Actually finding a simple scheme to do so seems daunting.
Posted by Jer
on 2013-08-20 11:19:35