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When buying an RV, owners are exposed to a number of new concerns they probably never faced with their regular passenger car. These include the actual weight of the vehicle, the weight distribution and its affect on tire durability.
Passenger cars are reasonable balanced side to side and if there is a moderate front/rear imbalance it is taken into consideration when the car manufacturer sets the recommended inflation for the tires as shown on the tire placard. Also car manufacturers will normally design with a safety factor of at least 10% to 20% on tire load capacity.
RVs are different. They have heavy components such as slides, battery banks, generators and holding tanks that can quickly result in significant side to side unbalance. Even multi-axle trailers can be unbalanced axle to axle, and that can affect tire life. RV manufacturers sometimes have tire load safety factors as low as 5% or less for an RV when normally loaded so it is easy to end up with significant unbalanced load and even overload on the tires.
Real life testing shows that half of the RVs on the road today have one or more tire in an overload condition. This is a undesirable condition as it can cause uneven tire wear and poor fuel economy. Even worse it can lead to tire failure if the unbalance is significant.
The best way to learn the actual loads on each tire position is with individual position scales. These are not to easy to find but you can check the RVSEF Weight & Tire Safety Program a service offered at many RV rallies and shows to see if you are traveling to a location where they offer the service.
If you can’t find a location to do individual tire position weights, you can use some regular truck scales such as CATScales or Certified Public Scales. Some farm co-ops or feed mills and some sand and gravel yards can also provide the needed service. You will need a scale with enough side clearance to weigh one side at a time ( see the worksheets) so check before you travel a long distance for a weighing. If single position scales are not available you will need to do some simple math to calculate your actual weights.
You can find worksheets at Fifthwheelst.com; similar worksheets are available from Michelin and Bridgestone.
You will not need to do this every trip or even every year unless you make a significant modification to your RV. Just be sure you have loaded your RV with everything you would normally take on a long trip and be sure to include water and fuel when you are getting your RV weighed.
Once you know the real tire loads you should consult the Load/Inflation tables. While most tables have similar numbers there are a few tires that are different, so it is important to use the tables published by your tire manufacturer. With all this information and the math done you select the minimum cold inflation based on the heaviest loaded tire on each axle. Motorhomes should generally set the cold inflation at least 5 psi or 10% higher than the minimum. Multi-axle trailers should set the cold inflation to the pressure molded on the tire sidewall but need to adjust the RV load so they have at least 10% “underload” as a Safety Margin.
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