Brand: Revisiting tire diameter on 4/AWD vehicles - Minneapolis Star Tribune
Q: While I agree that tires are an important safety component, I mildly disagree that they are relatively low-cost (new tires on my 2003 Expedition set me back over $1,100 two years ago). Even selling three lightly worn tires wouldn’t put much of a dent in the purchase price of four new tires. No doubt having a 16-inch tire mixed in with three 18-inch tires would cause many problems in a modern vehicle. But, using my Expedition as an example, its R20 tires are nearly 32 inches in diameter or approximately 1,024/32nds. Assuming that 3/32nds of tire wear would cause a 6/32nds decrease in diameter measurement, my worn tires would have a diameter of 1,018/32nds. My math is not great but to me that seems like the diameter of the worn tire would be about 99. 4% of the diameter of a new tire. Since you focused on percentages in your reference to tire wear, let’s do the same for replacement tire costs. The original purchase price of a 2003 Expedition was between $35,000 and $40,000. The $1,100 you spent on new tires represents about 3% of the original vehicle cost — a very small amount for the components most directly influencing the safety of... The original tire for that vehicle is a P255/55-18 with a diameter of 29. 06 inches. Tire wear of 3/32nds of an inch reduces the diameter by 6/32nds, leaving the tire at 28. 87 inches. Source: www.startribune.com
