Dear Tom and Ray:

This question is about optimum tire pressure. My father believes that front and rear tires require different pressures for optimal ride, safety, and economy. He says that one should adjust the tires to appearance, so you see a slight bulge when looking from behind the tire, rather than going "by the book." Please clear this up for me.
Barbara

RAY: Well, Barbara, your letter supports my theory that 98% of all misinformation about cars and driving is passed on by "fathers."

TOM: That's right. And the other 2% is passed on by us.

RAY: Your father is nuts, Barbara. In the 1950s and 60's, when most cars had bias ply tires, you could tell a tire was low by simply looking at it. But you can't do that with radial tires. And all but the oldest, and most decrepit heaps on the road (like my brother's '63 Dodge Dart) now use radial tires.

TOM: Radial tires can be very deceiving to look at. You can have one with 30 pounds of air in it, and one with 15 pounds, and they'll look identical! So forget trying to "eyeball" your tires.

RAY: Check your owner's manual and find out what pressure the manufacturer recommends (this information is sometimes on a decal on driver's door panel, or on the inside of the glove box door). That's the pressure you should use--give or take a couple of pounds. And check it with a good quality tire gauge, because that's the only way to know how much air is in there.

TOM: Now, if your father is distraught when he learns he's been wrong for twenty years, you should be prepared to toss him a bone of some kind. Fathers don't take news like this well. So tell him that he's sometimes right about the front and rear tire pressure being different. Some cars will recommend a two or three pound differential. It's not much consolation, but it may keep him from changing the subject to "financial advice."