Autopsy of a failed tire

I continue to see posts on various RV forums saying "I had a blowout on my tire. I checked the inflation every day and I didn't hit anything. It must be because it was a (fill in the brand)  or  because it was made in (fill in the location). I'll never buy that brand or tires made in that location again cuz they are junk."

If you are a follower of this blog you have seen this topic discussed previously but clearly there are folks out there who just do not want to be confused with evidence that doesn't support their pre-concieved notion of why tires fail.

Lets follow an "autopsy" of a failed tire and see if we can improve people's understanding of how to "read" a  failed tire so we have a better idea of the real reason it failed. If we don't properly understand the "WHY" then we probably will not take the appropriate action to prevent a re-occurrence.

 Here we note the size as 8-14.5. This is a low platform trailer tire. Many times used on Mobile Homes or construction equipment trailers. It is a bias construction and we can see the body ply at an angle.







We see this tire is a Load Range F (12 Ply rating) tire.
 


rated to carry  2835# at 100psi cold.

Looking at the tread we see the tire "looks" great.
 






As we continue to read the tire sidewall we see it was made in Thailand..
 




Now for some, that is sufficient. They say it wasn't made in the USA so it is a piece of junk. Lets continue and see if they are correct in their analysis.


 
The DOT date is 2812 so since this tire failed mid June 2013 or about 2613 the tire is only 1 year old and clearly since it came from Thailand there were probably 3 or 4 months for shipping and handling in a warehouse. Clearly the tire age is not the problem.

The first two characters of the DOT"2B" can be translated using out decoder web site  and we learn the tire was made by Deestone Ltd in Samutsakom, Thailand.

Continuing on we see the tire is Nylon body which would be consistent with a lower cost, bias, heavy duty construction.

Now we get to the interesting part. Looking at the actual area of the failure.
 In the picture at the top of this post you can see that both sidewalls have significant damage.

 As we look at the area of the tire that actually failed we see frayed cord.  This is what Nylon and Polyester look like when they fail in tension. Looking closer we see that not all cords are frayed.


These three cords have the look we see when we cut Nylon rope and fuse the ends with a lighter.


Warning Technical Information to follow:  Nylon and Polyester both melt in the range of 395°F to 495°F depending on the treatment and exact material involved. These materials also lose about half their strength when heated to over 300°F.


Looking even closer at those cords it is clear the ends are not frayed but fused. So we now have the physical evidence that parts of this tire saw temperatures approaching or exceeding 400°F. The only way to generate that kind of temperature is with rapid, extreme flexing.
 We see rapid flexing at highway speeds. We see extreme flexing when a tire looses say 50% or more of its proper inflation.

The heat in a tire comes from the bending of the cord material and radiates outward to the cooler surface.  It is illogical to think that only a few cords somehow flex enough to see high temperature and if we look closely all around the area of the most damage there are a number of cords showing similar heat damage.

So we now have physical evidence that proves operation at highway speed for a number of miles while the tire is significantly under-inflated.

Knowing this, I think you can understand that there was probably some other cause such as a leaking valve or puncture or cut of the tire that allowed the air to leak out over time. If the tire had in fact been properly inflated we would not see the 360° circumferential flexing and signs of high heat.

How do we avoid this type of failure?  Will changing the brand prevent air loss?  Will buying tires made in a different country prevent them from getting too hot when over flexed? Clearly neither of these "fixes" will prevent a reoccurance of this type of failure.

I would suggest a TPMS could provide warning if there is an air leak. That warning might be early enough to allow the driver to stop before the tire fails and maybe even before the tire is significantly damaged.

BOTTOM LINE
I would say that 95+% of tires I have seen with this type of "blowout" failure were in fact Run Low Flex failures. Having inspected many thousands of tires in my 40 years as a tire engineer, I have accumulated enough experience to be able to observe and find the physical proof of high heat damage similar to what we see here. Many times I can find and identify this proof in less than a 30 seconds. It's easy once you know what to look for.

Hopefully the next time you meet someone that says "I just had a Blowout" you will be able to identify the evidence that points to a run low flex so the person learns they need to know why the tire lost air. If it were say a leaking valve it certainly will do them no good to buy a new tire and mount it only to have it suffer the same fate.

Careful when you do research or before you buy

Recently I was asked to clarify some information an RV owner discovered as he did some research. What we see here is an error that is easy to make. Even for the more experienced RV owner.

The RV owner asked about a Michelin XTA
215/75R17.5 LR-J tire that came on a 5th wheel trailer. He had confirmed the load capacity of the tires at their max rated inflation and said they could handle the load on his 8,000# axles when inflated to the placard inflation of 120 psi. His question was about the max speed rating of the tires.



He consulted the Michelin Truck Tire Data Book and found that the subject tires were intended for Low Platform Trailer application.
In fact the brochure for his tires even identified the maximum speed rating for his tires as 62 mph.


He wanted to know if the maximum speed rating had been waved for RV application, and if it had what was the new speed limit. He found a statement from the Tire & Rim Association that specifically stating that when a tire had a speed rating below 65 mph it could not be manipulated (increased) with adjustments in inflation and load. He also found a Michelin truck tire service manual specifically saying that low bed trailer tires like the XTA, cannot have their speed increased.
Despite all this information he wanted to know how to work out the adjustments needed to allow a higher speed limit for the RV and could I please help him understand what he felt was confusing information given that the RV manufacturer had selected these tires for his trailer.

I had to tell him that in my opinion there was no way the speed limit could be adjusted. I pointed out that his error was in looking for information in data books and manuals of different type tires such as Truck Tires, RV tires and Low Platform trailer tires and assuming that since his tires were sort of like truck trailer tires and looked like tires he has seen on other large 5th wheel trailers, he could pick and choose which information applied to his specific tires.

The lessons to learn here are:
1. Not all RV manufacturers pay a lot of attention to proper tire selection for the application.
2. When doing research on tire type and specific operation limitations you need to look only at the literature for your specific tire if such literature is available from your tire manufacturer.
3. You cannot depend on the RV dealership to warn you about the real quality or limits of some components of your RV. You need to take responsibility for what you purchase. i.e. Let the buyer be aware.

Important Note:
Speed ratings are like the “Red Line” for your car, truck or motorhome engine. While it is possible to exceed the max speed rating of a tire just as it is possible to exceed the rev limit and run your engine in the red zone, I think we all understand that if we do run our engine that fast we are pushing the odds. In the same manner if your tires are rated for 65 mph max you might be able to run faster for a short time but you are consuming the finite limit of the tire structure and simply slowing down does not repair the microscopic damage you have done to the internal structure of the tire. You should not be surprised if you blow your tire just as you would not be surprised if you blow your engine after running in the red zone for engine speed.