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Friday, February 15, 2019

Small Single axle travel trailer tire inflation

I have received questions on tire inflation from folks with small single axle travel trailers, boat trailers, and utility trailers. There is some confusion, which I understand, so let's see if I can clarify my recommendations for inflations.

One common bit of information would be to learn the actual load on each tire position when the vehicle is loaded to the heaviest you ever expect it to be.
- For each axle identify the heaviest end and use that load when consulting tire load & Inflation tables.

Motorhomes  and Trucks
These vehicles would use the heaviest axle end load when consulting the Load & Inflation tables.

- The inflation needed to carry or exceed the measured load would be your MINIMUM inflation.
- I suggest you select inflation that will provide at least 15% "Reserve Load" for your Cold Inflation Pressure. Some find it easier to go with a +10% inflation over the inflation in the tables.
- Just be sure you have some Reserve Load capacity.
- I see no problem with running higher inflation as shown on the "Vehicle Certification Lable"

Trailers with a single axle
- There can follow the same guidelines as seen for Motorhomes.

Trailers with two or three axles
- Run the inflation molded on the tire sidewall that is associated with the tire "Maximum Load" capacity. many RVs show that inflation on their label, but it is still a good idea to ensure you have a reserve load capacity. SOme RV companies provide almost no load margin so it is up to you to make the appropriate adjustments. Running the tire sidewall inflation will give a lower Interply Shear force which, as you know, is a primary cause of belt separations on these RVs and are why tire life is about half what it is of comparable tires and loads on Motorhomes.
- Select the heaviest load as measured on all four or six tire positions and confirm that the tire load capacity at the sidewall inflation provided at least a 15% Reserve load.

For those interested in the science behind Interply Shear you might read this post.

Friday, February 8, 2019

Tire ramps or "blocks": Many can damage your tire

Last year I was at a large RV event

 and noticed many Class-B    RV were using various blocks or

ramps in an effort to get the RV level.
Here are a few examples.

None of the above are what I would consider acceptable. They all are too narrow or the tire is not properly centered.

The ENTIRE tread contact patch should be supported. On the left above you can see the contact patch and the size board I use.   
Too narrow or with part of the tread hanging off one side can put extra stress on the belt edge and result in the initiation of microscopic cracks that could grow into a Belt Separation.

If you have some of the plastic supports you first need to confirm they are wider than your tire. You also need to pay attention and be centered side to side and fore /aft on the support.