Saturday, July 24, 2021
Saturday, July 24, 2021

RV Tire Safety: Tire life – Why can’t I get a straight or consistent answer?

By Roger Marble
I’ve seen a number of posts on RV forums and Facebook asking why there are different answers to the question of when to replace tires in RV application, i.e., tire life. Some are told, “Replace at 5 years.” They may hear that as, “You will die if you drive on a 6-year-old tire.”

Discount tire has presented this diagram:

Discount Tire – Tire failure

You will note that they do not show some cliff that you fall off.  I responded to a question on tire life where the person thought that the tire companies were simply pushing tire sales.

Tire “life” is not an on-off switch. Rubber begins to lose its strength and flexibility the day it is put in the tire warehouse. Temperature and time are the primary drivers of the loss of strength and flexibility.

Tires can fail for a variety of reasons

Hitting potholes creates cracks in the internal tire structure. Most are microscopic but all cracks grow and none repair themselves. So the number and size of cracks simply grow till one day the rubber will not be strong enough to tolerate hitting a pothole or piece of road debris. In addition, the heat generated with a long run at high speed on a hot day simply lowers the remaining strength of a tire.

The more a tire is driven, the more flexing it experiences. Older tires, having lost some of their flexibility, will experience more actual tearing rather than stretching. Driving faster increases the rubber temperature. The higher the rubber temperature, the faster the rubber loses its ability to stretch and recover. 

My post on tire covers pointed out the “aging rate’ of tires doubles with each increase in operating temperature of 18 degrees F.

Part of Organic Chemistry is chemical reaction rate

In addition to the rate of aging doubling for every 18F increase in operating temperature, heat also comes from being in the sun when parked. So if the RV is parked with tires in direct sunlight, you can see the tire achieve 36F increase or more. That means it is aging at more than four times the rate it would have if in full shade.

If you want to understand the technology behind this accelerated aging due to heat, I suggest you can read some of these sources if you have a few hours:

Wikipedia: Reaction rate

ThoughtCo.: Factors that Affect the Chemical Reaction Rate

Here is an article on tires:

Correlation of Rubber Properties between Field Aged Tires and Laboratory Aged Tires

The idea that tires be replaced after 5 years of use is based on probability. Some tires fail at 3 years of use and some are still running after 9 – but it’s the odds that can get you.

If you have an RV trailer, I can assure you that the science shows that backing into an RV site is much harder on the tires than pulling through. This is because the Interply Shear is much higher backing in because the side forces are much higher. I wrote about that force in this blog post.

Have a tire question? Sign up for Roger Marble’s new Facebook Group: RV tire news, information and discussion, hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.

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

 ##RVT1007

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J J
20 days ago

Will you please explain what “in service” means? Every tire life guide I’ve read uses that phrase, as does your picture above, but none have explained it.

For example, the tire date codes on our Ford F-53 motorhome show they were manufactured in September 2018, the VIN (chassis) build sheet shows a January 2019 date, my motorhome has a “build” date of May 2019, and we accepted delivery in July 2019.

While ours is just a nine month difference, some people have reported they purchased new tires that had a date code from a year earlier.

My guess is the “in service” date is when the tires were mounted, which probably was January 2019 when Detroit Chassis LLC built our F-53 stripped chassis. But what does “in service” mean for real or does it not really matter?

Thanks.

Roger Marble
17 days ago
Reply to  J J

I would suggest you contact the tire company’s local dealership. They should be able to clarify their definition which might not be the same as some other brand tire. In general, I would consider it to be the date of original sale to you.

Rock & Tina
20 days ago

I was excited to read what Roger had to say on this as he is a tire expert and all the online non-experts have strong opinions on when to replace tires. I’m sorry to say I was very disappointed in this article because I would classify the whole article as a non-answer. He discusses the various variables and how they affect tire life but then fails to draw any conclusions. How about a simple answer like properly maintained and inspected trailer tires should be safe on average for “X” years and a similar statement for Motorhome tires. Come on Roger, you’re the expert, render an expert opinion.

Wayne C
20 days ago
Reply to  Rock & Tina

The title of the article is “Why can’t I get a straight or consistent answer?” Not when should you replace tires. Roger provided a list of variables that explains why a straight or consistent answer can’t be given.

Wayne C
20 days ago
Reply to  Wayne C

I found the limit of 7 years the hard way for the way I use my tires. My tires looked perfect, and were running 90 psi @ 90 degrees F (according to the TPMS) when one tire shed its entire tread in one piece and the casing ruptured. The fender got rumpled a little and a propane line was rearranged but fortunately little other damage. For me based on that experience my limit matches Discount Tire’s recommendation of 6 years. The tire shop looked at the casing and said the tire had probably simply timed out.

Roger Marble
17 days ago
Reply to  Rock & Tina

I understand you would like an answer like 46.5 months but even you mentioned “average”. So would you accept “average of 46.5 months +/- 26 months”? I doubt it.

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