RV Tire Safety: Are sidewall cracks a cause of tire failure?

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with RV tire expert Roger Marble

I recently read an RV forum post about sidewall cracks. From the picture, it appeared the tire had what I would call Ozone or UV cosmetic cracking. The owner was concerned about the tire durability as he had suffered a couple of “blowouts” previously.


My response:

Not being able to inspect the “blowout” tires or even see some pictures, I have no idea for the reason for the tire failures, as “blowout” is not specific enough to suggest a possible cause. They might have been run for a few miles while losing air. They might have suffered impact damage 10 or 100 or 1,000 miles prior to the ultimate failure. They might have been run overloaded or underinflated or over speed recommended by tire manufacturer or tire industry engineering guidelines for thousands of miles.

Yes, tire failures can be expensive if the failure is only discovered by operating the tires at speed and not during the regular detailed close inspection by a “qualified specialist” as outlined in the Michelin Tech bulletin on RV/Motorhome tire inspection.

It is also true that sidewall cracks, in my professional experience, are not in themselves the root cause of tire failure. Just as a person developing a temperature of 101 F or 102 F is not the cause of an illness but is just an external symptom. Tire sidewall cracks are an indication of extensive tire age with the cracks developing due to time, temperature, flexing and exposure to Ozone and UV – all of which are detrimental to tire life.

“Zipper” sidewall failures of steel body ply are the result of fatigue from operating for miles when significantly underinflated or overloaded or a combination of those. Sidewall crack inspection guidelines published on pg. 8 of THIS guide suggest a maximum depth of about 2/32″ on large radial tires (22.5″ sizes) which usually have rubber thickness closer to or thicker than 0.10″.

Tires “fail” for two basic and different reasons:
1. Sidewall flex failure from low inflation/high load; and
2. Belt separation from long-term rubber degradation due to excess heat and age.

I covered these in two separate posts in 2012 and again with a slightly different focus in 2014.

While I can conceive of someone running tires for many miles with sidewall cracks that get deeper than 2/32″, those cracks would need to penetrate deeper and get completely through the sidewall rubber to the depth of the steel and then water would need to be introduced and enough time pass to allow a significant portion and number of steel cords rust and be weakened before a “zipper”-like failure could occur.

The above would, in most cases, take many months of operation and would require that no, or improper or incomplete, inspection take place before a tire would suffer a catastrophic failure.

So the bottom line is two-fold:

1. Ensure you are not overloading your tires and that they are ALWAYS inflated to what is needed  for your application by running a TPMS.

2. Starting at 5 years (3 years in trailer application) from the DOT manufacture date molded on the tire sidewall and annually or every 2,000 miles, whichever comes first, have the tires inspected. I have covered the topic of inspection previously.

 

Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.

##RVT923

 

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Alvin

Roger. I own a 25 foot Class C, with 30,000 kms (18,000 miles) on it. Driving the Pacific coast highway this summer past, I noticed the left outside dual low, so I checked and indeed it had lost 15 lbs of air. From where I did this I could see a Les Schwab Tire store down the way so I dropped by to have the tire checked. After finding a faulty valve stem the guy said to me “you have bigger problems than a valve stem my friend – you’ve got some major cracks on the sidewall”. We checked the rest of the tires and they all had the same cracks on the sidewall and upon closer inspection inside each tread, The tires looked like 14 year old tires. How I never noticed this I have no explanation for except with a virtually new vehicle I guess I wasn’t looking for this – and I should have.

This vehicle is not over loaded, and as a retired mechanic know enough about a vehicle to monitor tire pressures religiously. I asked him what his opinion was about the safety of the tires, and predictably he told me if they were on his vehicle he would not chance driving very far on them, especially in the terrain we’d be travelling back to Alberta Canada 1000 miles away.

I recorded numbers and took pictures.

When I told him the vehicle was two years old and had the mileage on it it does he couldn’t believe it.

Consequently, I changed all six tires on the spot, driving the mountain passes of Washington, Oregon, Idaho and Montana I did not want to chance ending up floating down a river at the bottom of a canyon.

These were factory installed Michelin’s. They’ll hear from me about this, but I’ll tell you two facts. This is my third Michelin tire set failure on a Recreational vehicle – this being my last.

BobG

I definitely agree with Roger’s overloading comment. I’ve seen and read situations where the owner knows they’re overloaded, and simply inflates their tires to the max reading on the sidewall, and believes they’re good to go.

In that case, running down a hot road for hours, is asking for (and often brings) disaster, just as sure as under-inflating tires.