It’s best to replace 2 or 4 tires after flat

reality, most people will want to replace their tires before they get that worn out.

Studies show that stopping distances are much longer on wet roads when tread depth gets below about And performance on snowy roads degrades below And because you bought an allwheel-drive vehicle, Chen, I’m guessing that weather is an issue where you live. That means those 7’s are already getting near the end of their useful lives.

If you have different-size tires on the car, the wheels will always be turning at different speeds, adding lots of wear and tear to the differential. And center differentials are expensive.

So what do you do now? Well, manufacturers have different recommendations about how similar tires should be to one another (check your owner’s manual). But most suggest a tread difference of no more than or inch. So if you’ve got two 7’s and a 12, you’ve got a problem, Chen.

One solution is to keep the new tire you bought and buy three more. That’s expensive, because you still have useful life on the three tires you’d be throwing away. But that’s the best option from a mechanical point of view.

Another option is to have that new tire “shaved” to match its axle-mate. That involves taking a perfectly good, new tire, and paying a tire store $30 to turn it into a tire with 15,000 miles on it. Most people resist that idea because it seems wasteful.

But when you compare that with the cost of three more new tires, shaving or matching the new tire might be the way to go.