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Sunday, February 24, 2013

Tire Crack or Cut ? CSI - Akron

More than once I was presented with an almost new tire with a claimed "defect crack". I believe that the owner was many times asking for a refund. While the decision to refund the price of the tire or to replace the tire or to deny the claim was not my job. My job was to do a detailed "autopsy" and issue a report. Here is one such case.

A tire was presented with the identified area of concern as seen in this picture. You can see the area of concern does appear to be a jagged crack about 1.2" long.

TIP. To enlarge the pictures to see the "Witness Marks" left by the cutting object right click and select open in new  Tab or New Window. Then you can close the Tab or window and return to this post.

Looking down into the "crack" I noted what appeared to be "witness marks" that would be left by a cutting object. You can think of these much like Ballistic fingerprints left on a bullet by the rifling of the gun. as seen in this picture of a bullet.
For examples and detailed explanation see pg 8 of THIS presentation.

If some object cuts a tire it will leave straight line marks much like those seen on the bullet. If there is simple rubber tear or a molding defect, there will be no such straight lines.

 After deciding where to cut so as to not destroy the evidence, I was able to spread the area open to confirm the presence of the witness marks. There have the appearance of small ridges or lines in the rubber.
Here is the piece I dissected out of the sidewall. You can easily see the lines of the witness marks left by the knife I used to remove this piece.

In this picture you can see the witness marks in the "cut"..

Then I looked at the side of the area and discovered that at its deepest point the body cord was cut.

Cracks in a tire can grow through the rubber but not through body cord.

 The external cut would be in the top of this picture and the "examination" cuts I made are from the bottom.

Closer examination confirm the body cords were cut from some external sharp object and not from any manufacturing defect as seen in these final pictures.

I think you will all agree that there was no defect and that some sharp object cut the tire sidewall.

Tire inspection is a real science and knowing what to look for and how not to contaminate or destroy the evidence as an inspection is done is what takes years to learn. I think you can also see that having pictures of the whole tire cannot provide sufficient detail to arrive at the "Root Cause" of the tire condition.

1 comment:

  1. Thank you for tire autopsy 101. No wonder the RV world is so far ahead of everyone else. Keep articles like this coming.


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