Some people want to claim a tire is "defective" and present the tire for a free replacement because of a bulge in the tire sidewall.
There is no question of there being a sidewall bulge, but my job was to actually look at tires and determine if the tire actually had a defect.
We look for marks on the wheel
When we look for evidence of some mysterious "defect," we might notice marks on the wheel, as seen in #67-5, and notice the "witness mark" on the wheel left by the tire being bent over the edge of the wheel that matches up with a mark on the tire sidewall.
Some of the marks are subtle.
Some marks on the wheel and tire are not so subtle, as seen below.
Sometimes the wheel was even bent when the impact was so severe.
And sometimes the tire sidewall even "polished" the wheel.
An inspection of the inside of the tire at the location of the bulge seen in the first photo in this series reveals some broken body cords.
How does fishing relate to tires?
In my seminars and training classes I usually can find someone who fishes. I ask if it's possible to catch a 10# fish with a 5# leader line and they respond "Yes." I then ask if it is possible to break a 10# leader line trying to catch a 5# fish and they say "Yes." When asked how, they point out that you can break a 10# leader with a 5# fish if you jerk the fishing line, as the jerk is a "shock load" on the fishing line.
I then thank the person for pointing out how it is possible to "break" or "snap" the tire body cord with the "shock load" of hitting a pothole or some other road debris.
While not every pothole hit will result in a broken body cord, in almost every case of a large sidewall bulge there are broken cords present. Some are visible on the interior of the tire, as seen above.
Other times, the cord is still broken but does not result in the interior rubber being broken if the tire is dismounted before it has been driven many miles, as seen below.
What I found on my vehicle's tire
As a side note, the picture below is a different tire than the series seen above. Tire #02-30 was actually a tire removed from the left front of my personal vehicle. A sidewall bulge was discovered by chance when an oil change was being performed.
After dismounting the tire, I reverse bent the tire to place the interior under stress, which exposed the location of the broken cord. This break happened when I was driving. I can honestly say that I do not remember hitting a large pothole or piece of road trash, but the evidence is incontrovertible. I definitely hit something hard enough to break the body cords.
Close inspection can often reveal the evidence that helps the investigator learn the root cause of the tire failure.