Dealership's Service Department Earns a C Average

Dear Car Talk:

After getting dealer service on my 2016 Toyota Corolla with 16,000 miles, the car started to shake at 60 mph. I drove for a couple more months, but the shaking did not go away.

I finally checked, and the tires were over-pressurized to 51 psi, 19 psi higher than indicated on the door pillar. The dealer evidently inflated the tires to what was the maximum pressure indicated on the tire itself, rather than the recommended pressure.

I had them look at it again and they recommended new tires because I still had the original tires from the factory. I declined, opting instead to have the tires rebalanced. I spoke to the manager, who insisted that over-pressurization would not result in increased vibration, and that 7-year-old tires should be replaced anyway because they are easily damaged. He also emphasized that driving the car as little as I do can make the tires worse.

A couple of questions:

1. Should I replace a 7-year-old set of tires with very low mileage on them? The treads are almost brand new.

2. Could over-pressurizing an old set of tires result in the wheels needing to be rebalanced?

Thank you so 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 high-speed 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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