Sidewall Cracking or "Dry Rot"

[tireman9]

"Dry Rot" is a misnomer for cracking observed  on tires, usually more observable on the sidewall. Rubber simply does not rot like an old tomato.

Tire age in itself is not a serious concern but it can be part of a diagnosis or predictor. What is of concern is the elasticity, flexibility of the rubber at the belt edges and the adhesion of rubber to the steel in the belts and body cord. The problem is that it is impossible to know for certain, these conditions without doing what is known as a "cut tire examination". This is when tire engineers use power band saws and large cutting equipment (visualize a 12' tall guillotine with a 12" wide 1" thick blade sharp enough to cut paper, driven by a hydraulic cylinder with a few thousand pounds force pushing on the blade)  to slice and dice a tire so the above characteristics can be accurately evaluated.

In my career I conducted or was involved in many thousands such examinations. We would correlate the external condition of the tire before it was cut with the actual condition of the internal components. While one can never be 100% certain or accurate of a prediction, with thousands of such examinations under our belt we could be pretty confident that our appraisal would be reasonably accurate.

Given that you would not want to destroy your tire trying to learn it's internal condition what is done is to use an externally visible condition of degraded external rubber i.e. cracking as a rough predictor of the internal condition. In general the more external cracking the more likely it is that the internal rubber could fail and tear due to a loss of elasticity. However external condition is not absolute as it is sometimes possible to have the external condition be worse than "nominal" if solvents were used to clean the tire or there was excessive exposure to sunlight. This can be observed by comparing tires that spend most of the time in southern states with one side of the RV facing South. I had a situation where the gel coat of the fiberglass side of my RV itself suffered significant cracking from UV exposure.

There are other tools such as X-Ray that can identify if there is already a separation of the internal components which is used by retread shops but it would cost you significant time and money to dismount your tires, have them inspected and then decide if they go back on the RV or were scrapped. It could approach the cost of a new tire for the handling and process plus you would be with out tires for a few days to complete the inspection. So this is why we generally use sidewall cracking as an approximate predictor along with the tire age and sometimes a free spin inspection to help identify tires with a suspected internal separation before the tire comes apart.

So we need to all understand that cracking is a bit like taking your temperature when you feel ill. An temperature elevated by a few degrees in itself is not going to cause "failure" or death but it is a symptom that can be used along with other symptoms to help your doctor diagnose your internal condition. Is the doctor 100% accurate? No, but with experience and training they can present diagnosis that are probably correct or at least very close.

So maybe you can now understand why there is no absolute predictor of "end of life" for a tire based solely on calendar age. We need to use a number of different observations to reach an opinion that has a high probability of being correct.

 

[wildebill308]

On 5/23/2017 at 5:24 PM, Tireman9 said:

So maybe you can now understand why there is no absolute predictor of "end of life" for a tire based solely on calendar age. We need to use a number of different observations to reach an opinion that has a high probability of being correct.

My observation is that tires between 7-10 years old fail at a significantly higher rate than tiers between 5-7 years old. I wonder why Michelin would say this if age was not a consideration. 

"While most tires will need replacement before they achieve 10 years, it is recommended that
any tires in service 10 years or more from the date of manufacture, including spare tires, be
replaced with new tires as a simple precaution even if such tires appear serviceable and even if they have not reached the legal wear limit.
For tires that were on an original equipment vehicle (i.e., acquired by the consumer on a
new vehicle), follow the vehicle manufacturer’s tire replacement recommendations, when specified (but not to exceed 10 years)." 

This is from a Michelin Technical Bulletin dated May 15, 2006, I have seen nothing to change it.

Bill

[hermanmullins]

Question on Michelin tires: Do they have a different way of showing the mfg. date? Was looking at a coach yesterday and couldn't come up with an understandable date code. Or all 6 of the tires had the codes on the inside. Just wondering. 

Thanks, 

Herman 

[manholt]

Bill.  Is that Quote for Car Tires or Truck Tires?  I don't run car tires!    I will not go against a professional opinion.  Don't forget the Liability rule and Disclaimers!

[manholt]

Herman.  DOT on inside off tires...I run across that often, including 3 of mine!  I know where you where, why would you not be looking at tag coaches'?

[jleamont]

Herman, sometimes they are on the inside . When I put my new ones on I made sure they were facing outwards on all but the rear inners.

[hermanmullins]

Carl, it was a coach with a tag. But you can only see 6 tires, remember the 2 more on the duels.

What I didn't see was the imprint with something like "21/16' or "21-16". The closest I saw was a "symbol 213".

I also turned the coach down quickly. Many more problems then just the dates on the tires.

Herman 

[wildebill308]

Carl, The quote was from the TRUCK tire web site.

http://www.michelintruck.com/reference-materials/manuals-bulletins-and-warranties/

The heading of this bulletin was "Service Life for RV/Motorhome Tires".

So yes I think it is relevant to RV/Motorhome tires.

This bulletin also shows a date code.

Bill

[wolfe10]

Yes, the full DOT number with the date code is only molded into one sidewall of each tire.  Depending on the installer, it could be facing toward the outside or the inside.

It is generally in a slightly raised/indented area at the end of the full dot number, since that part of the mold has to be changed weekly.  It is a 4 digit code with no spacing.

So, 4112 was made the 41st week of 2012.  If a three digit date code the tire was made in the last century, as the date codes went from 3 to 4 digits on 1/1/2000!!!

[tireman9]

Yes older is more likely but the reality is that if a specific date is given and a tire fails before that date the tire company gets sued. Also if a tire runs past that data then the tire company will be accused of cutting the time in an effort to sell more tires.

The general guideline is to not run any tire that is older than 10 years old. There are some applications such as on multi-axle trailers 3 to 5 years is the normal max.

Which of you has ever had a jug of milk go bad before the "expiration date? Who has had the milk still good days after that date. The issue is that we are dealing with organic material which can have numerous variables.

 

RE DOT date. If you are still having problems get with me in Indy in July  or Syracuse in Aug.

 

Side note everyone should learn the full DOT serial of all their tires and write that info down and keep it with other important documents That way if there is a recall you don't have to go read your tires but just review your documents.  I have suggested that if you aren't comfortable getting down and trying to find the DOT you find a teenager, give them a flash light and maybe an inspection mirror and have them read the serial to you. It's probably worth a few bucks.

 

You might also read my blog post of DOT date code.