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.

If I upsize my RV’s tires, can I lower their inflation?

I recently received this question from an RVtravel.com reader regarding using larger tires with lower inflation to get a more comfortable ride while maintaining safety and not overheating the tires. Hi Roger, I have a tire question for you. I own a 2021 RV with a GVWR of 8596 lbs. that I purchased used in the spring of 2024. The factory 205/75R15 Goodyear Endurance tires were manufactured in November 2019, and I believe they are due to be replaced. I am considering replacing them with GY Endurance 225/75R15 for the increased load range to give myself a wider margin of safety, as the 205s’ load range is basically equal with the GVWR for the camper. The question My 205s are rated for 2150 lbs. at 65 psi, which is what I’ve been running them at. According to the Load/Inflation chart, I could theoretically run the 225s at 50 psi for the same 2150 load. Obviously, I want more load capability so I would run them at a higher psi, say 55 or 60. But is it safe to run them at a lower psi since they are rated to 2830 lbs. at 80 psi? I don’t need that much load capability and would prefer the softer ride of a lower pressure as long as it’s safe to do so and not be overheating the tires. Please let me know what you think with regards to running this particular tire at less than max psi. —Jeff D. My reply Hi Jeff, First, it’s essential to understand what the “GVWR of 8596 lbs.” means. The Gross Vehicle Weight Rating (GVWR) is the heaviest your RV should ever be. In fact, the RV Industry Association (RVIA) recommends that the tire loading should be no more than 90% of that number. Additionally, certain assumptions are made when arriving at that number, namely, that the load on your tires is evenly split between the axles and that the load on each tire on an axle is evenly distributed from end to end. RVSEF (RV Safety & Education Foundation) has measured the actual load on tires on tens of thousands of RVs and learned that more than half of the tires in RV usage are being overloaded. This data supports the recommendation that, at a minimum, every RV should get on a truck scale and at least learn the weight on each axle. Getting “4-Corner Weights” is not always convenient (see RVSEF), so I suggest we assume one end is supporting 53% of the axle total. Going to this effort is important as the inflation in the tables is the MINIMUM inflation for the heaviest loaded individual tire, and all tires on the trailer should have the same cold inflation. You mention “safety” a few times. Tire inflation safety is not an on/off switch where tires will quickly fail if you drop 1 psi below the table number or run for 10 years if you are a few psi above the minimum. You can review my posts on this blog, but here is my specific answer to your question. The short answer to the question on new tires Yes, you can go up in load capacity IF you also go up in inflation and up in Load Range. I recommend you confirm the load on each axle when the RV is fully loaded to the heaviest you ever expect to be (full water, food, tools, clothes, people, etc.) by getting on a truck scale. Use the scale reading from the heavier axle and apply the suggested 53% figure to arrive at your tire loading number. Consult the Load & Inflation tables for your size and Load Range tire to learn the MINIMUM cold inflation that you would use for all four tires. On my RV, I use the above and then add 5 psi to that number and make sure my inflation never drops below the Minimum by reading my TPMS display. I hope this isn’t too much info. Roger Marble