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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.

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