What's the ideal air pressure for my tires to achieve maximum fuel efficiency?

Dear Car Talk

Dear Car Talk | Aug 01, 1995

Dear Tom and Ray:

As a senior citizen on a fixed income, I try to save as much gas for my car as possible. I have heard that keeping your tires inflated to the maximum, or a little over, can save gas. Is it true? My car is a Buick Century, and they advise 28 pounds of air, which seems low.

TOM: If 28 pounds is what the manufacturer recommends, that's what you should use, Ann.

RAY: It's true that you'll increase your gas mileage slightly if you over-inflate your tires, but the money you save on gas will be more than offset by what you spend on new tires... and possibly your hospital bills.

TOM: There's friction between your tires and the road. That's what allows the car to "grip" the road. We call this "traction." And you need this traction to make the car go, stop, and turn.

RAY: When you over-inflate the tires you reduce the friction (because the tires get taller and thinner and there is less rubber touching the road). And because there's less friction, it's true that you do increase your gas mileage.

TOM: But there are lots of problems. Not the least of which is that you ALSO reduce your traction. That means you can't go as well, turn as well, or stop as well. And that increases the likelihood that you're going to crash into something.

RAY: Plus, your tires wear out a lot faster, because the wear is concentrated in the middle of the tread--the only part of the tire that's still in contact with the road.

TOM: And to make matters worse, a severely over-inflated tire is always in danger of exploding.

RAY: And most importantly (in case we haven't been persuasive enough) we want you to inflate your tires correctly because WE don't want any harm to come to you, Ann. You see, our editor told us we can't afford to lose any more readers. If we do, she's going to replace us with what she thinks is a much more useful weekly column. I think it's called "Tropical Fish Training and Grooming."

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