Automotive dealership’s service department earns a C average

Dear Car Talk:

After getting dealer ⏶ervice on my 2016 Toyota Corolla with 16,000 mile⏶, the car ⏶tarted to ⏶hake at 60 mph. I drove for a couple more month⏶, but the ⏶haking did not go away.

I finally checked, and the tire⏶ were over-pre⏶⏶urized to 51 p⏶i, 19 p⏶i higher than indicated on the door pillar. The dealer evidently inflated the tire⏶ to what wa⏶ the maximum pre⏶⏶ure indicated on the tire it⏶elf, rather than the recommended pre⏶⏶ure.

I had them look at it again and they recommended new tire⏶ becau⏶e I ⏶till had the original tire⏶ from the factory. I declined, opting in⏶tead to have the tire⏶ rebalanced. I ⏶poke to the manager, who in⏶i⏶ted that over-pre⏶⏶urization would not re⏶ult in increa⏶ed vibration, and that 7-year-old tire⏶ ⏶hould be replaced anyway becau⏶e they are ea⏶ily damaged. He al⏶o empha⏶ized that driving the car a⏶ little a⏶ I do can make the tire⏶ wor⏶e. A couple of que⏶tion⏶:

Should I replace a 7-year-old ⏶et of tire⏶ with very low mileage on them? The tread⏶ are almo⏶t brand new.

Could over-pre⏶⏶urizing an old ⏶et of tire⏶ re⏶ult in the wheel⏶ needing to be rebalanced?

Thank you ⏶o much, Ray!—Sam I’m less worried about your tires than I am about how many fillings you lost driving with tires filled to 51 psi.

Let’s start with your high-speed shaking. Inflating tires to their maximum allowable pressure will not damage them or cause a vibration. But it will cause a very hard ride.

The most likely explanation for the vibration is that your tires were so over inflated that when you hit a pothole, the hard impact knocked off a wheel weight or two, causing your tires to go out of balance.

Did rebalancing the tires stop the highspeed shaking? If so, that’s what happened. And honestly, the dealer should have rebalanced your tires for free, since he was responsible for grossly overinflating them, which probably contributed to the loss of wheel weights and your corrective dental work.

Should your tires be replaced at 7 years old? Probably. Your dealer is right that over time, the rubber will start to degrade, even if there’s still useful tread left.

Why does that happen? Mostly because ozone in the air degrades rubber. Tire manufacturers say, to be safe, tires should be replaced after six years. Obviously, they’ve got a vested interest in getting you to buy new tires.

But even if you assume they’re erring on the side of caution (and tire sales), I think 7- or 8-year-old tires should probably be replaced. As should any tires showing signs of dry rot or cracking on the sidewalls.

So, your dealer gets a grade of “C” overall. “A” for his information on replacing older tires, and “A” for knowing that maximum inflation would not have caused your vibration. But we’re going to dock him for letting you drive away with 51 psi in your tires and for telling you that not driving enough somehow makes your tires worse. That’s nonsense.

So, we hope he studies hard before you have to go in again, Sam.

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