What are sidewall Bulges, Bumps or Depressions?

This question about a tire sidewall bump was originally posted by an RV Travel reader: We had a new-to-us travel trailer. When we stopped for gas, the station attendant had this horrified look on his face and showed us bulges on 3 of the 4 tires. He also showed us a pile of tires out back that he said had all “Blown-Out”. We bought 4 tires with a higher load rating. We took the bad tires with us on our whole vacation. After we got home, I tried to get a warranty from the RV company, but was told, “We do not do warranties on the tires.” I then contacted the tire manufacturer. The customer service manager stated that the part where the cords overlapped was the strongest part of the tire. I called “BS”. I tried to contact other departments at the tire company, but got no replies. Why are tire companies allowed to sell these defective tires? I found the RV owner’s comments interesting but rather confusing. One moment, he is talking about depression, the next about bulges. Tire bulge versus depression There is a big difference between a “bulge” that sticks outward from the rest of the tire sidewall and a “depression” that goes inward toward the air chamber. Most radials will have one or more sidewall depressions. These occur due to the small overlap of the body cord ply that occurs when the tire is being “built.” These depressions would actually be locations of more cords in that location that prevent the inflated air from bulging a tire outward when inflated. A bulge, as seen in the pictures below, would be the result of either an “open body ply splice,” which would be a warranty issue, or the bulge could be the result of an impact where body cords were broken. In this case, the tire clearly hit something, and the body cords are broken. This condition is not covered by any “warranty” unless a “road hazard” warranty was purchased. I have covered impact breaks, with pictures, that I discovered on my personal car and on my wife’s car, and posted the results of the forensic tire inspection with pictures on my RV Tire Safety blog. Understanding the difference between a “bulge” outward and a “depression” inward in a tire sidewall will save you much aggravation. With close inspection in good sunlight, you can look at your tires and find one or more depressions in every one of your tires. Holding a short (approx. 6″) straight edge against the tire sidewall will help you discover the depressions that are in your tires.