RV manufacturers must certify the tires and tire pressures required to support the vehicle. On drivable RVs, there will be a Federal (or Canadian) Motor Vehicle Safety Standards (FMVSS/CMVSS) compliance label (data plate) in the area of the driver’s seat. (The label shows the Gross Vehicle Weight Rating (GVWR), the individual Gross Axle Weight Ratings (GAWR), and the Gross Combined Weight Rating (GCWR) that was determined by the final body-builder or manufacturer. The manufacturer will certify the capacity of the vehicle as it was built with the tires and tire pressures required to support this capacity and this will be shown on the label.
Tires on motorhomes are often considered “truck” tires although many are specially manufactured for RVs. The RV tires often have high weight-carrying capacities and a UV protectant in the rubber. Ratings marked on their sidewalls show the maximum carrying capacity based on a maximum tire pressure for both single- and dual-wheel configurations. If you should lower the air pressure, you will reduce the capacity of the tire and the amount of load-carrying capacity of the RV.
Tire Load Charts
You should contact the tire manufacturer and obtain the tire load charts or the booklet that specifies the weight-carrying-capacity for your tires at various tire pressures. It is strongly recommended that you do this. Their information will also include how to properly check your tire pressure (always when cold), how to safely add air (remember, 105 pounds of pressure in a tire casing is high pressure and potentially deadly if the tire blows), and how to determine how old the tire is (the DOT Code). You can usually find tire load charts on the tire manufacturer’s website.
You may hear talk among RVers about adding some extra air for safety. Tire manufacturers used to recommend increasing the tire pressure by ten percent (10%) above the amount required to carry the load you determined by the weighing process. Theoretically, this provided a margin of safety and allowed for the natural depletion of air pressure as time passed. However, that 10% recommendation is now built into the tire ratings for the RV type tires. There’s no need to add more.
Monitoring and Checking Tire Pressure
One of the best options for knowing your tire pressure is to use a tire-pressure monitoring system. These work in any vehicle including a motorhome. These systems sense the tire pressure in all tires at all times and send a signal (tire-pressure reading) to a monitor. The monitor is usually located up front for the driver or co-pilot to see it if needed. The tire pressure can be read for any tire on the vehicle or one that is being towed.
For example, if you are driving a truck and towing a fifth-wheel, the monitor will read all the tires on your truck plus all the tires on the fifth-wheel. If you are driving a motorhome and towing a car, the monitor will read all the tires on your motorhome (8 tires if you have a tag axle) plus all the tires on the car you are towing.
These systems will give a loud signal at some level of loss of tire pressure. For example, with a slow leak, you tire pressure will go down and this may take several days. At some point (programmed into the tire pressure monitoring system), when the tire reaches a predetermined percentage of loss—for example, 12%—the monitor will beep loudly and will indicate which tire had that loss of pressure. If that happens, it’s time to check it now.
For a blowout, you get the same signal. The blowout causes the tire pressure to instantly go down so the monitor gives the same signal.
One of the major factors in tire wear and failure is under-inflation. (On a side note, under-inflation will decrease your fuel mileage as well.) It is imperative that you know the weight of your RV and how much air to put in your tires. Therefore, to be safe, comply with the laws, and save money, know your RV weight and tire pressure. Load your RV carefully and knowledgeably. Plus, make sure to frequently check your tire pressure when cold at the start of each day. Use a good quality, accurate tire pressure gauge or monitoring system to accomplish this.