Tire Autopsies - Run Low Flex Failure and Impact break

 I thought it might help to show a few examples of what was observed while doing a "Tire Autopsy".

A tire would be received with a complaint letter. The letter might say something like " I was driving down Route 66 at 55 mph when suddenly I had a blowout. I wasn't speeding and had checked the inflation just that morning. What is wrong with your tires? There must have been a defect.

The tire looked like this. 

 

 

 

 

 

 

Another view 

On close inspection I found what looked like a hole in the upper sidewall where the

rubber had been worn away.

 

 

 

 

 

 Using a bent paper clip,

 

 

I was able to confirm the hole

 

and looking inside we can see where the puncturing item

went.

Note a bent paper clip will fold at the bend if you try

 and push it through a tire sidewall, but if there is a

 hole the paper clip can follow the hole.

For this case I provided the above information and pictures.

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Another complaint involve a bulge in the tire sidewall.

 The location was marked by the tire dealer.

On the inside we see a lump

We can also see a dark curved line where the tire

had extra bending.

By cutting away the rubber from the inside of the tire,

down to the body cord we can now see the broken

cords from the impact.

I trust that after seeing these examples you have learned that

sometimes additional examination is required to find and 

confirm the actual failure.

After doing hundreds of similar examinations it allows the

experienced examiner to quickly identify that the reason for

 a tire failure was not some design or manufacturing "Defect",

but the result of external causes.

More like thin in future posts.

"Optimal Inflation" or not?

 Many think the RV sticker (aka tire placard)

 

 

 

 

 

 

 

or in tire Load & Inflation tables

 

 

 

 

 

 

PSI number is an "Optimum" pressure when it is in fact, it is the MINIMUM pressure needed to support the GAWR which assumes a perfect 50/50 side to side split which is unrealistic.

We tire engineers want to ALWAYS protect the tire from overload. We know that pressure will change with changes in the Ambient (air temperature in the shade). We also know that tires will always get warmer when they are driven.

The pressures found in the Load & Inflation tables are almost universal across all tire companies (a handful of Michelin sizes differ by 5 psi or so, so not significantly different) and they are not playing games with tire engineering science.


Unless there is a specific reason, which should be mentioned in a post, we are ALWAYS talking about "cold" inflation pressure as we know that tire pressure changes by about 2% for each change in temperature of the tire as I covered in these posts.


The Short answer to all tire inflation questions.
1. Get the weight on each RV axle from a truck scale (or similar)

2. If you do not get individual tire position weights (aka 4 Corner weights) assume the heavy end of each axle is supporting 51 to 53% of the axle total.

3. Consult tire Load & inflation tables to learn the MINIMUM inflation to run based on the heavy end of each axle.

4. I suggest that your cold inflation on all tires on that axle, be _at least_ 110% of the MINIMUM psi found in the table in #3 above, but do not exceed the max inflation rating for your wheel. (number may be on the wheel or you may need to consult RV company).

5. *Always* run a TPMS with the low pressure warning level set to the pressure in #3 above ( this might take some calculation effort as different TPMS have different ways of setting the warning level.