By Roger Marble
Can tire failure start a fire? The quick and short answer is: Yes, it is possible – but it is also highly unlikely.
After reading a statement about RV fires being started by tire fires that were themselves started by a tire failure, I felt compelled to jump in with some facts.
While it is true that tires can burn and be difficult to put out once they are on fire, it is also true that it is difficult to start a tire burning.
According to Wikipedia: “Tire fires are normally the result of arson or improper manipulation with open fire. Tires are not prone to self-ignition, as a tire must be heated to at least 400° Celsius (750° Fahrenheit) for a period of several minutes prior to ignition.”
Now, I can almost hear some saying: “Yeah, but what about a tire blowout?” Well, let’s consider a tire failure. You are driving down the road at 50 mph or more and there is a sudden, loud “BANG”. You are startled but with luck and skill, you can pull off the road to look at the damage. Most likely you find a tire in multiple pieces along with some damage to your RV. What you do not see are pieces of burning rubber strewn along the road. If we consider the process of a tire coming apart, it may be easier to understand why we don’t see burning rubber when we stop because of a tire failure.
There are two main reasons for tire failure
Consider the two major reasons for a tire to fail: (1) The belt separation where the belt and tread detach or become separate from the body of the tire; and (2) The sidewall fails because of excessive flexing while being driven at extreme low inflation (usually with a 75% or greater air loss).
If we look closely at the sidewall flex failure of a regular Passenger, LT or Trailer tire we will see that the body cord is usually polyester surrounded by various rubber compounds. The process of over-flexing or over-bending while running at highway speeds at the same time can result in the polyester overheating. This can result in the polyester actually melting, as seen in this picture of fused poly cords:
and in this picture:If you stopped right away, the tire might look like this – where we can see the “melt line” running 360° around the tire sidewall.
Think for a moment what you do when you cut a piece of nylon or polyester rope. You get out a lighter or match and fuse the end.
Polyester loses half its strength at 300°F to 350°F and melts at about 480°F. This is a far cry from the 750°F ignition point of tire rubber.
The second mode of tire failure, belt separation, takes many hundreds or even thousands of miles to result in a tire coming apart. If the tire has a nylon cap ply, you occasionally may see signs of some of the nylon melting at 430°F. We see that the rubber that is holding the belts together fails by “de-vulcanizing” or reverting to its uncured state and loses almost all of its strength. This occurs at about 348°F.
Is it possible for tire failure to start a fire?
Having covered the examples of why it is unlikely that a tire failure can start a fire, the question remains: Is it possible? The answer to that is yes, it is possible to start a tire on fire – but this usually occurs when the fire started with a brake or bearing failure that ignites the axle grease or even the brake fluid – which both have an ignition temperature of about 550°F.
Someone is probably thinking about their steel body radial on their big Class A RV. No, they do not have polyester or nylon that can melt, but the rubber in those tires can still revert and lose all it’s strength and still be 200°F under the ignition temperature.
A final observation: We need to remember that tires are being run 24/7 at tire plants around the world with most being “run to failure,” yet we simply do not see tire test labs suffering tire fires initiated by the failed tires.
I hope you understand why I would say: Please do not spread the false narrative that tire failures start tire fires. The facts just do not support that claim.
Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.
I remember seeing a news report some years ago about a forest fire started by sparks from a flat tire on a toad, but I think the sparks were caused by the wheel dragging on the pavement. When that happened to my toad, a tire came apart and wrapped around the axle so the steel wheel wasn’t turning. I probably dragged it less than a mile before someone passed me waving and honking as I was wondering why the tail was wagging, by the time I got stopped the wheel had a flat spot and was hot enough to melt the asphalt on the shoulder, but no rubber burning.
A good example of why having a TPMS on every tire that you have, is a good idea. The cost of an extra $35 sensor would have easily been covered by the cost of the wheel and even the tire too.
A little off subject but did you ever experience or investigate tire pyrolysis? From the video in this link I would think a hot brake or failed wheel bearing could cause this to happen.
I’ll admit to being one to get out the heat to solve mechanical problems and I was lucky enough to survive 62 years before being made aware of this potential problem.
Wayne, Thanks for the video. I can understand that welding on a wheel could damage a tire to the point it would fail. The video was not discussing open flame of a tire fire. As I have pointed out in my blog, the use of a TPMS sensor on a bolt in metal stem might provide a warning of a dragging brake or bearing failure by reporting the wheel temperature.