Tips for determining the inflation pressure for your motorhome tires.
By Brett Wolfe, F252125
To determine the correct tire pressures for your motorhome, neither Michelin nor Goodyear recommends using the inflation pressure (psi) imprinted on the tire sidewall. That psi is correct only for carrying the maximum weight, which is also imprinted on the sidewall.
Instead, it is recommended that motorhome owners consult the RV tire guides provided by the respective tire manufacturer. You will see that these companies do not have a single recommended tire pressure for each size tire. They provide a chart wherein the correct pressure is based on the actual weight supported by the tire.
So, how do you determine the correct pressure for your motorhome tires? The best way is to load the motorhome as it would be when you are going on a trip and then have all four (or six) wheel positions weighed individually. The Recreation Vehicle Safety & Education Foundation (RVSEF) performs this service at all FMCA international conventions and other events. Of course, you can just use an axle weight, but in that case you are assuming that the weight is distributed evenly on each side. The problem is that equal weight distribution rarely occurs on a fully loaded motorhome.
Using the heavier wheel position on each axle, consult the tire manufacturer’s weight/psi chart for your tire and determine the correct minimum pressure. All tires on an axle should be filled to the same pressure based on the heavier wheel position. Many owners add 5 psi to 10 psi to that as a safety cushion. Add a little more safety cushion if all you have are axle weights, to account for side-to-side imbalance. However, do not exceed tire or wheel maximum pressures.
If obtaining individual wheel position weights is not possible, look for the vehicle’s weight rating information on the Federal Motor Vehicle Safety Compliance label, which by law will be posted in the driver’s area. On the label will be the recommended inflation pressure based on maximum gross axle weight ratings. Here you are assuming your weights are not higher or lower than the maximum. Keep in mind that the air pressure recommendations on the label are for the tires with which the motorhome originally was equipped.
The least desirable option when trying to determine the amount of air pressure to have in your tires is to look at the psi recommendation imprinted on the sides of the tires. This psi figure assumes that you have no information related to the load the tire will be carrying. That pressure rating could be right on “” hopefully not, since that means you are loaded to the maximum GAWR “” or it could be off by 20 or more psi.
All tire manufacturers’ recommended tire pressure are based on cold tires (before being driven) at the ambient temperatures you will be experiencing. Anyone who tells you what pressure your tires should be inflated to without weighing your motorhome is not providing accurate information. For example, the “correct” minimum tire pressure from the Michelin book for a 275/80R22.5 is 75 psi if the load is 4,500 pounds, and 115 psi if the load is 6,175 pounds. That’s a significant difference!
How Old Are Your Tires?
Molded into the sidewall of every tire manufactured is a code that indicates when and where the tire was manufactured. This code is required by the United States Department of Transportation, and the identification number starts with the letters “DOT.” The two digits following the letters DOT indicate the plant where the tire was made. The last group of numbers “” a four-digit code “” is the one that discloses the week and year of manufacture. The weeks of the year are numbered consecutively, and the last two digits of the year are included. So, for instance, the code 4711 indicates that the tire was manufactured during the 47th week of 2011, specifically, the week of November 21.
This information is especially important for the owners of motorhomes. Motorhomes aren’t always driven as many miles as the typical passenger car, so motorhome tires often wear out as a result of age-related issues rather than mileage. Because so many variables are involved, it is not possible to provide a replacement date based simply on the calendar. So, motorhome owners need to keep their tires properly inflated and also have them inspected regularly by a tire professional, such as a dealer. Once a motorhome tire reaches 5 years of age, it should be inspected at least once a year by a tire professional for signs of wear and aging that would indicate the need for replacement. Most motorhome tires will need to be replaced before they reach 10 years from the date of manufacture, but, if not, they definitely should be replaced at this point as a safety rule, even if they still appear to be serviceable.