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Monday, Apr 21, 2014
Autos

Never underinflate tires on purpose

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Dear Tom and Ray:

I like a bit more comfort, so I lower the pressure in my tires by 4 psi below the door-sticker recommendation. I figure that the pressure listed on the door is for the car when it is carrying five people. There are never more than two people and a bag of groceries in my car. My brother, who also drives a Lexus LS 430, says that this practice is unsafe, but he’s the kind of guy who cleans his instrument panel with a Q-Tip. What do you guys think? — Richard

RAY: Wait a second. The ride in a Lexus LS 430, with its feather-pillow-like ride, isn’t comfortable enough for you? Do you wear pants made of broken glass, Richard?

TOM: You might want to rent a Jeep Wrangler for the weekend. That might put a new perspective on the “terrible ride” of your Lexus!

RAY: Well, if for whatever reason you want a softer ride, lowering your tire pressure below the manufacturer’s recommendation is not the way to get it.

TOM: Underinflation is dangerous. You may remember the famous exploding Ford Explorer tires of the early 2000s? One of the factors in those failing Firestone tires was said to have been underinflation.

RAY: There were other causes involved. There was heat, high speeds and questions about the tire design and build. But one of the results that came out of that disaster was a new public awareness of the importance of keeping your tires correctly inflated. You must have been absent that day, Richard.

TOM: Eventually, the federal government mandated tire-pressure-monitoring systems in all new cars so that people couldn’t drive around on an underinflated tire without knowing it.

RAY: So I’m guessing your Lexus must be more than a few years old and doesn’t have one of those low-tire-pressure warning lights. Because if it did, the light probably would be on now.

TOM: The light will come on when pressure drops about 10 percent below the recommended number. So if your car calls for, say, 33 psi in each tire, a drop of a little more than 3 pounds of pressure in any tire will set off the idiot light.

RAY: The problem in your case is that, while your “reduced” tire pressure of 29, or whatever it is, may not be seriously low, if you ever were to get a leak, your pressure would go down from there. And you’d very quickly be in danger of overheating a tire.

TOM: So go apologize to your brother, tell him he was absolutely right and buy him a new box of Q-Tips to clean his instrument panel as a peace offering. And fill up your tires!

You can listen to Tom and Ray Magliozzi’s “Car Talk” program at 10 a.m. Saturdays on National Public Radio station WUSF, 89.7 FM.

Got a question about cars? E-mail Click and Clack by visiting the Car Talk website at www.cartalk.com. They can’t answer your letter personally but will run the best letters in the column.

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