Question
Tire
Barry, I noticed the other day a slight ridge-like depression on one of the rear tires of my Jeep. It runs vertically down the sidewall from near the tread down toward the rim, maybe 2 inches long. Its only noticible upon close inspection, or when the light hits is just right. I attached a photo.
Something to be concerned about?
AnswerJason,
This is called an indentation (or when grouped with bulges, undulations). They are caused by the overlap of ply cords in the tire building process - where the flat sheet of ply cords is turned into a hoop shape. This overlap is called a splice - and this area of the tire is stronger than the surrounding area (2 layers instead of one!)
Every tire will have at least one per ply. The indentation may be difficult to see, and rubbing your hand on the sidewall may make it easier to find. (On the sidewall of the tire, there will be a listing of how many plies a tire has and what they are made out of.)
Sometimes the tire builders will make a large splice (lots of cords) and that will make the splice more visible. Sometimes the tire builders will stretch the plies and there will be a bulge. Bulges are always a bit of concern, and if a bulge is ever found, the tire should be replaced.
I should mention that bulges can also be caused by breaking the cords by impacting an object like the curb. In the cause of an impact caused bulge, this is not caused in the manufacturing process, so it is not a defect and not adjustable. A manufacturing related bulge (one that is always adjustable) will be visible immediately after inflating the tire. So a bulge that shows up many thousands of miles after the tire was applied is most likely an impact related and while it should be replaced, compensation should not be expected.
But indentations are nothing to worry about. They do not cause vibration or any other type of problem - except for being a bit unsightly.
