Common Tire Problems
Cracking and Bulging
The Diagnosis: This usually comes from hitting a pothole, curb, or debris. Under-inflation and over-inflation put tires at a greater risk of damage from impacts. Large cracks in the sidewall that runs along the rim are either impact-related or caused by chronic under-inflation. Numerous small cracks in the sidewall or tread blocks come from exposure to the elements and age. Rubber, much like your leather interior needs treating to prevent cracking, by using a tire and rubber protectant. Bulging is what looks like a pimple in the tire, most often in its sidewall. It happens when there's an impact that causes internal damage, but the damage doesn't show up until weeks or months later. With bulging, you're looking at buying a replacement and the tire should be removed from service, regardless of the cost. Eventually, it will fail.
Cupping (Also Called Scalloping)
The Diagnosis: It happens when worn or damaged suspension components cause the tire to bounce as it travels, coming down harder on some spots of the tire than others. Bad shock absorbers are the usual cause, though anything that connects the wheel to the rest of the car could be a culprit. Be careful with your diagnosis, though. Even tire shops sometimes incorrectly identify feathering or heel-toe wear as cupping. A wheel that is out of balance may also cause cupping or bald spots to form, though there will be fewer hills and valleys than you'd see with cupping caused by a failed shock absorber.
It Looks Like: Feathering, only the ramps run front-to-back along the tire rather than side-to-side. The leading edge of the tread blocks will be worn smooth while the trailing edge will be sharp. The Diagnosis: "[It's] definitely one of the most common conditions we see," "Because it's so common, a lot of people think it's normal." Heel-toe wear is typically a symptom of insufficient tire rotation intervals. So check your car's maintenance schedule and make sure you keep up. Misalignment or worn or damaged suspension bushings, ball joints, and wheel bearings can also cause heel-toe wear.
Feathered tread blocks are shaped like a series of ramps in a directional wear pattern that goes sideways across the tire. The lower edges of the ramps are rounded while the higher edges are sharp. If you can't tell by looking, run your hands across the tread blocks. The Diagnosis: Most often, feathering means the car's toe setting (a measure of the car's alignment) is off. If the toe setting is correct, a worn or damaged suspension bushing could be causing the car's alignment to shift as you drive. Check for worn or damaged ball joints and wheel bearings as well.