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Old 01-27-2015, 07:40 PM   #1
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Trailer tire "Side loading"

I came across a page, that has to do with fifth wheel towing, but this part completely applies to travel trailers too. Instead of simply linking to the page, I am sharing it here. I want everyone to read and understand some of the whys and wherefores of trailer tires and tire stresses. You will also see that just because a trailer looks good, does NOT mean it is still good. This also helps explain why trailer tires are only good for 5 years. It also explains how tread separation can and does occur. There is a short youtube video, that explains what side loading is. That video is HERE. He also recommends that tires be inflated as follows: "Option One: Per the minimum tire requirement stated on the vehicle's Certification Label." "Option Two: No less than the tire's cold PSI molded on the tire's sidewall and not exceeding the wheel/rim PSI rating."

The page I got all of this information from is HERE

"Interply Shear" and other Techno Babble
by Roger Marble (Edited for clarity.)

Bottom line... FIRST


When a radial tire is loaded, the belts and body have to bend from a round shape to a flat shape in the area that contacts the road. Additionally, when you turn a corner, the forces generated to move the RV sideways have to be transferred through the tire structure. This causes additional bending of the belt and body structure. Increased bending causes increased stretching of the rubber. With enough stretch, microscopic cracks form and existing cracks get bigger. Eventually with enough cycles and enough force, cracks may grow and this increases the possibility of tire components separating which could lead to a tire failure. You can lower tire stretching if you decrease bending and you can decrease bending if you increase tire inflation.

Engineer Speak and Techno Babble
If you own a multi-axle trailer, tire bending forces can be much higher than those seen on a tow vehicle, motorhome or car. Tires on these types of vehicles are not close together and are located at the corners of the vehicle.
Special consideration for multi-axle trailers. Warning, this gets technical.
When not driving in a straight line, there are significant side loads on multi-axle trailers because the tires are fighting each other; this is because the axles are not "pointed" to the center of the radius of the turn. These loads cause interior structural tearing. Sometimes, loads may be 20% or more higher than those seen in tires on non-trailer applications. Initially, tearing begins at the microscopic level, but with time and repeated cycles, these microscopic tears grow, which can lead to small cracks at the belt edges as seen here at the arrows.



If not spotted, these cracks continue to grow to almost the full width of the tread as seen below.



If you are lucky, you will see the bulge in the tread as seen on the left. Clearly, you know this tire has failed and MUST be removed AT ONCE as the separation can grow and can cause a belt to come off the body of a tire. You can lower these forces by either decreasing the load by at least 20% on the tire (probably not something you want to do or may not be able to do) or you can increase the inflation to stiffen the structure which will decrease the slip-angle. In this case, you could increase the tire inflation from the minimum inflation needed for the static load to the inflation associated with the max tire load as molded on the tire sidewall. BUT, you need to be sure you are not exceeding the max rating of the wheel/rim.

Therefore, the best recommendation I can give to trailer owners is to run the max inflation molded on the tire sidewall.

I hope this helps everyone understand more about their tires and also helps us all be safer, while enjoying the whole towing/camping experience!
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Old 02-02-2015, 08:47 PM   #2
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Hi Gary,

I see you find Roger's blog. Good deal and thanks for sharing. I had missed that one oddly enough. He is a good guy and helped me with my tire saga trying to figure out "why". A retired tire engineer gone RV'er.

The pics above are actually from my tire failures. I cut up the parts and sent them to him for review. He then sectioned them knowing what he was looking for.

Here is my story, ST Tire Failure Analysis (Lots of Pics)

Thanks

John
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Old 02-02-2015, 08:51 PM   #3
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Quote:
Originally Posted by JohnB View Post
The pics above are actually from my tire failures. I cut up the parts and sent them to him for review. He then sectioned them knowing what he was looking for.
Yeah... Those pics had your name all over them.. I was just waiting for you to verify my suspicions!
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Old 04-10-2015, 04:48 PM   #4
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Glad you found my original post informative even if it was a bit technical.
If others have tire related questions, other than what brand they should buy I will be happy to offer an answer.
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