Dear Tom and Ray:

My husband and I share a 2002 Subaru Baja, which we love. We often drive it on tough four-wheel-drive roads in the mountains and deserts of Southern California, and it has never let us down. However, I have noticed that the sidewalls of the tires are becoming worn, and in one place, the black "rubber" coating has been scraped away and a white underlayer is exposed. This patch is about an inch by a half-inch, close to the outside edge of the tire. My husband and I disagree about the seriousness of this. He thinks the injury is cosmetic and should be ignored. I think it is serious and could result in the tire de-laminating on the highway or somewhere in the remote outback. Since he is the one who looks after the car, I really cannot insist on new tires. However, I am worried. Could you put my mind at ease? -- Daphne

RAY: No, we can't, Daphne. I'll tell you a little story. One time, I had a terrible ringing in my ears. And after a week or so, it was driving me crazy.

TOM: So he goes to the hospital, and he sees a world-famous eye, ear, nose, throat and wallet specialist named Dr. Patel. Dr. Patel does a thorough examination and asks my brother a bunch of probing questions. And then he announces his diagnosis, which is that my brother has tinnitus: ringing in the ears.

RAY: And I say: "Tinnitus? What causes that?" And he says, "Well, Raymond ... it could be nothing." Then a look of excitement lights up his face and he adds, "Or, it could be a brain tumor!"

TOM: That's the story with your tires, Daphne. It could be something cosmetic, or your tires could be falling apart.

RAY: When a tire has raised white letters, oftentimes those are produced by building up several layers of rubber, then buffing off one layer and exposing a white layer of rubber below. So that would be the "it could be nothing" explanation.

TOM: On the other hand, there are white-colored structural elements in there, like the carcass ply, which is the polyester "ribcage" that holds the whole tire together. And there are the steel belts themselves, which would look more metallic or shiny, but could appear to be white. Those are the tire equivalents of brain tumors. Those would need to be addressed immediately.

RAY: So, one thing to look for is the texture of the white material that's been exposed. If it's exactly the same texture as the rest of the tire's exterior rubber, that increases the likelihood that it's just another layer of rubber.

TOM: But if the texture is any different, if it has any kind of fibrous feel or if you see any crisscrossing material, you may have exposed something much more important.

RAY: The bottom line is that you need to take it to a mechanic or tire professional you trust, and find out exactly what's been exposed. See if you can get a more definitive opinion than the one Dr. Patel gave me. And by the way, my tinnitus went away a few days later and never came back.