Bulges and indentations can be nothing to worry about or a serious problem.
Being made out of rubber (and a bunch of other stuff, but we’ll stick with rubber for now) tires are pretty flexible. They need to be, in order to deal with changing road conditions. Tires made entirely out of stone, regardless of what cartoonists would have us think, simply don’t work very well.
It is this very flexibility that helps to give modern tires their strength and resilience. However, it can also lead to indentations and bulges.
There’s nothing unusual about small indentations in the sidewall. These indentations (or “undulations” as they are sometimes called) are a purely visual condition. Tire performance is not affected at all. In fact, they are very often found on radial tires as a characteristic of the tire construction process. The indentations are more noticeable on larger tires, because of their taller sidewall, and on tires that operate at the higher end of the inflation pressure scale.
Tires are reinforced with cords of fabric, usually a synthetic such as polyester or nylon. Radial tires have at least one layer of these cords, more if it is a heavy duty tire. The cords run parallel to each other but sometimes overlap. This overlap can cause a slight indentation when the tire is inflated to full pressure.
These indentations may not look great, but they are harmless. Even if they appear on a newly installed tire you have no cause for alarm. The same cannot be said for bulges.
Bulges appearing on the sidewall of a recently installed tire are definitely bad news. In most cases, these bulges are the result of a space between some of the body ply cords inside the tire. When this happens with new tires the solution is simple: return the tire.
This situation is almost invariably covered under the manufacturer’s warranty. This is a workmanship/materials defect, and it is not the fault of the technician that installed the tire. Although tire manufacturer’s do a lot of testing before the tires reach the marketplace, this is a problem that just doesn’t show up until the tire is installed and inflated.
If you’re tires have developed a bulge a significant amount of time after being installed, then it probably isn’t the materials that are at fault. Ply cords, though by no means delicate, can be damaged by impacts with curbs or road hazards, or by running into potholes. If this happens, it’s time for a visit to your local tire dealer.