回复：1万5千迈的车,换胎必须一对吗?

15kmi could wear out about 2mm in diameter in fully inflated state. That is to say, if you put a new same tire on to it, the new one could be 2 mm bigger in diameter than rest of them.

Although it is not ideal to have one slightly bigger tire, due to the following reasons, it is ignorable:

(1) Tire manufacturing isn't a rocket science. Tire making is of a process of molding, there are variances of material density, roundness and elastricity, etc... Using a simple term, they are never perfect. If you put 4 new tires on to the wheels and inflated, measure them, you'll find that their variance might be bigger then 2 mm. Your concern is within the vaiance so it is ok.

(2) Think about a set of same tires worn after 40kmi, due to individual habit, car careness, many people keep driving their cars without rotations for years. The uneven wear on the tires differs greatly. Those four tires won't be same size. Do people still drive it causing problems? Apparently not.

(3) When one tire is slightly bigger, what impact will be to the car, specially to the wheel? In a perfect world and driving in perfect straight line, the bigger tire wheel will turn less to keep all tires travelling same distance. How to make this happen? The answer - the differential gears adjust the turns. However, in real world, as only you are not driving perfect straight line, the differential gear will constantly adjust the turns, so for a 2mm bigger tire, it won't add much extra burden to differential gears.

(3) What is the strategy? After you buy a new tire, if your car is front wheel drive, put that one in front driver side; if your car is of rear wheel drive, put it at rear driver side. The reason? You want to wear this new tire faster. Weight increase the tire wear. When you drive the car only yourself no passengers, your body weight added to left side...

Just my 2 cents...