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Friday, August 26, 2022

Can you do a tire "Autopsy" at home?

 When you have a tire failure many people are only interested in replacing the tire as soon as possible. But there are others that want to understand the "why?" of the failure so they can take the steps necessary to avoid a re-occurrence of the problem for if you don't know the real basic reason for the failure any corrective action you might take may not actually "fix" the problem.

Think of a car not starting. If you jump to the conclusion that the reason for the non-start, is a bad battery when it really is the first signs of a failure of the starter motor or a failure of the ignition switch, the new battery will not "fix" the no start problem will it?

Now I am not saying that everyone needs to have the tools and skill to do the "autopsy" shown below but when I was working as a Forensic Tire Engineer I was expected to dig deep and to learn the real reason for a tire to fail. 

It is in my basic nature to be inquisitive, so when I was contacted by an RV owner who had what he thought was a tire about to fail I decided that I could help him learn and understand the "why" when he started asking questions as many engineers do.

The following is what we did and what we learned.

As you can see the tread is very round.


This is not normal for a steel belted radial tire.

John, the owner measured the OC of all 4 tires and found a big difference with one tire being an inch larger than the others.

Clearly something was different this tire.

After removing the tire from the rv and looking closely at the tire he noticed that one portion of the tread seemed to "bulge" outward.


His next step was to confirm the tire was no longer round.


 After de-mounting the tire and inspecting the interior he said he could not find any indication of failure. At that point John contacted me and after some back and forth I told him how to dissect the tire so he could ship the tread portion to me for a more detailed inspection.

You can see the work he had to do to get the tire tread area cut from the rest of the tire.


This was John's effort to

find the belt separation,

but he was not sucessful.

When I received the tread my experienced eye quickly found the location of the belt separation.

This level of effort on John's part was extraordinary but we got the evidence to prove a belt separation as the reason for the bulge in the tread area.

Now you don't need to go to all this effort as a simple "Free Spin" inspection as seen in this YouTube video will provide the evidence you would need to decide if it is time to replace your tires.

I have recommended that owners of RV trailers do a "Free Spin" inspection once a year or every 2,000 miles. This schedule might line up with when you inspect brakes or re-pack the wheel bearings so the Free Spin is not any additional effort and if you discover a wobble or bulge in your tire you know that it's probably time to replace it rather than wait for it to come apart on the side of the Interstate. 

Wednesday, August 17, 2022

Weigh the RV each trip?

Was following a thread where some people were saying they adjust tire inflation each trip based on how much "stuff" they are carrying. I didn't think this was a good policy so offered the following: 


Unless you are making significant (1,000# or more) changes in what you pack in your RV, I see no reason to be messing with tire inflation once you have finished adjusting axle alignment and been on a scale to learn the actual load on your tires. The general advice for weighing is to have the RV loaded to the heaviest weight you expect to travel with. This means full of cloths, books, tools, water, fuel, food, spare parts and toys you might travel with. There is really only one inflation number you need to keep in mind and that is the MINIMUM inflation required to support your load. We are trying to protect the tire from failure and with data from RVSEF showing that over half of RVs historically have been running their tires in overload. Damage to the tire structure is caused by the rubber bending and stretching past an elastic limit at the molecular level. This stretching actually breaks some of the chemical bonds and once broken the resultant cracks never repair or reform themselves. They can start small as seen here.

 The cracks only grow. Once formed the cracks will just get larger and larger till eventually they get large enough to result in a failure of the structure which many times is in the form of a belt detachment from the body of the tire as seen here.

  It doesn't take too many miles for a tire in this condition to come apart and you may end up with a nice "Blowout" unless the tire is replaced before the crack gets too big. The inflation in the Load & Inflation chart is the MINIMUM you should run but heat, age and the tearing a tire experiences from hitting pot holes can result in the rubber cracks forming even if you are running the inflation found in the charts. Running higher than the minimum inflation, can offer some protection as the tire will run cooler and bend less which means less tearing of the rubber chemical bonds. If you look at the tables you can see that each increase of 5 psi gives you a few hundred pounds more load capacity and conversely each drop of 5 psi decreases the load capacity of your tires. Tandem axle trailers place some additional stress called Interply Shear, on the tires which result is more cracking and more tearing of the rubber bonds. I would recommend against lowering tire inflation once you have learned the inflation required to support your heaviest weight. I also recommend that you set your TPMS Low Pressure warning level to no lower than 5 psi below the minimum inflation learned from your scale reading as I can think of no reason or benefit to ever run an inflation lower that what is needed to support the load. In fact, on my RV, I run my inflation at a +10% margin over the inflation from the tables which allows me to set the TPMS low pressure warning level to the inflation requires to support my heaviest scale reading.

Friday, August 12, 2022

Strange wear on trailer tires - Camber Wear Not proof of a "Tire Defect"

 If you have one shoulder of a trailer tire showing more wear than the other as seen here,








You probably have Camber Wear. Unlike the front end of your car or truck few RV trailers have  alignment that can be adjusted with hand tools. BUT the first thing you need to do is confirm you are out of alignment

Assuming that the axles are still firmly bolted to the trailer frame and there are no obvious bent or damaged spring shackles you might need the help of a professional RV Trailer Alignment shop as seen in THIS video.

But you might want to first confirm that you even need to have the axle replaced or "bent".

 You can measure your Camber and the Toe-in.

Low cost Camber Tool....

 How to measure TOE at home. This video is not of an RV trailer but it does a good job of showing how to be sure the axle is square. While this is on a car you should be able to see that we are looking at having the front and rear of the two tires on the same axle being the same distance apart.

Here is another trailer having the axles measured

 I tried contacting Lippert to learn the alignment specs for Camber and Toe but they would not give me the information without providing the VIN and other info on the trailer. I don't understand this as logically Camber should be near 0° and Typical toe-in specs vary from one-thirty-second to one-eighth-inch with closer to 1/32" being better for tire wear.

I did find these Reference Documents for Lippert Axles


Friday, August 5, 2022

"Defect Reporting"

I have asked RV owners who had tire failures if they have reported the failures to NHTSA or to the dealer that sold them the RV. Almost universally they said they didn't bother or were told by the dealer "it's not their job". 


The reality is that it is Federal law that tire failures be reported to US DOT. "defect reporting requirements, the focus of this memorandum, the TREAD Act requires automakers to notify the Secretary of Transportation within five days of discovery of a defect or the need for a safety recall. See 49 C.F.R. § 573.6." There are significant fines for failure to comply. NHTSA complaint needs the RV VIN and the complete tire DOT serial including the date portion.

 It is my opinion that if you have a failure or suspect failure and can't bother to file a complete report and include a picture you really have lost much of the right to complain about tire quality as you are effectively keeping the information from the tire company and from the Federal Agency that can order a recall after an investigation. No investigation will ever start because you posted a complaint on Facebook or an RV Forum.