Get a group of RVers together—online or at a rally—and there is always some curiosity, confusion, a few myths, a half-dozen rumors, and a guess or two about weighing your coach. Where is easy… truck-stop scales, grain elevators, cement plants, batch plants, some state’s weigh stations, and at major RV rallies to name a few. But most of the time we avoid the really important issue in all of this… that is, why weigh your coach? There is only one really important reason to weigh your coach (okay, two if you count just being curious).
The really important reason to weigh your coach is so you can set your correct tire pressure—one of the most confusing things confronting RVers but one of the most important for your safety and costs!!! Here are some facts…
- Tire pressure must be the same across an axle for driving safety. (Each axel has two wheels/tires on it. The tire pressure needs to be very close.)
- Under-inflated tires will wear out much faster!
- You cannot determine your correct tire pressure unless you know your coach’s accurate weight for each individual wheel position.
First, what is gross weight? For our purposes here, it is the coach fully loaded and ready to use. Before you weigh it, fill everything— all five tanks, i.e., fresh, grey, black, fuel, and propane tanks. Then load the RV with all the stuff you are really going to take with you—canned goods, books, clothes, food in the fridge and freezer, all the kitchen stuff, tools, and even your horseshoe collection (if you are really going to take it with you)! Then, when you get it weighed, both the pilot and copilot need to be sitting in the coach, in the front seats, like you normally drive it.
You can always get your coach weighed before anything is loaded (a new or used coach) but in doing so, you will have to guess at balancing your load when you finally move in. Additionally, weighing empty does not provide the information to determine that you may be simply overloaded.
Knowing your gross weight is fine for the curious. Knowing your front and rear axle weights is a bit better but will only tell you if you are overloaded in the front and rear. While nice to know, as standalone data, you still won’t know much about your coach.
However, knowing your individual wheel position weights will instantly tell you how your load is balanced—front to back and side to side. Your weight (load balance) needs to be within about 5% across an axle, i.e., side to side. You have no control over the location of the fresh, grey, and black tanks and due to the weight of liquids, these will influence your load balance.
Back to Tire Pressure
Why is this confusing? Simple, the correct tire pressure for your RV must be calculated—it cannot be “given to you.” Your correct tire pressure is not some standard setting related to tire size and definitely not what your friends say they use. Two factors are used to calculate your correct tire pressure—the size of your tires and the coach weight at each wheel position. “Whoa,” you say, “my tire pressure is stamped into the side of the tire.” True, but you can’t rely on that one either!
There are two reasons for this. First, the setting stamped into the side of the tire is the minimum cold tire pressure (psi) allowed for the maximum load. Second, your tire pressure will be different for the front and rear (single and dual-tire pressures) even though the tires are the same size! Go ahead and use that setting as a starting point—as a temporary setting until you get your coach weighed correctly and calculate your correct tire pressure. It should be noted that “temporary” does not mean after the 3,000-
mile trip you are planning!
Since tire pressure increases as the tires get hot from driving, your ultimate tire pressure should be set when the tires are hot. So, you need to get the individual wheel positions weighed, drive 20-30-40 miles, and then adjust your tire pressure for each tire based on your calculations. I know, this sounds like it’s more work than it’s worth but one time every year or so can help keep you safe and save you lots of money on replacement tires.
When something (a balloon, beach ball, or tire) is inflated, the air pressure in that object can be measured. You’ve done this before and have checked your car’s tire pressure many times over the years. When that same object is under external pressure (such as squeezing the balloon, sitting on the beach ball, or loading your RV), the amount of air pressure is increased since the object is being squeezed. The amount of air in the object is the same—you did not add more air—but the space containing the air
shrinks—becomes smaller—because it is being squeezed.
So, the major lesson here is that as you load your coach, your tire pressure increases. How much? Nobody knows. Therefore, your correct tire pressure cannot be calculated until the coach is fully loaded and each wheel position is weighed.
Tire manufacturers provide a chart to help you determine (calculate) correct tire pressure after weighing the individual wheel positions— different manufacturers have different charts. Knowing the individual wheel position weights on your coach is first—without that information you cannot do anything except guess. After you know those individual wheel position weights, then you have to determine your tire pressures (likely different front to rear) from their charts.
You will also need the tire manufacturer’s explanation of how to read their chart correctly. Both single- and dual-tire pressures are given. When you locate your individual wheel position weights on the chart (for your tire size), it will indicate your correct hot tire pressure for that respective weight at that particular wheel position. Only then will you be able to correctly set your tire pressure after the tires are hot.
Most drivers of cars and light trucks have, at some time, checked their tire pressure. Interestingly, most of us do not check this unless we notice something out of the ordinary—you glance at the tire and the sidewalls seem to bulge out too much or a friend mentions it to you. It is usually a simple matter of going into any gas station or tire store, using a tire-pressure gauge, and if needed, using their air hose. The suggested tire pressure is given in the Operator’s Manual, on the side of the tire, or the tire store will likely have a chart of suggested settings. It’s easy.
There are no visual clues for RV tires. There are no “tricks” you can use to determine tire pressure. You may have seen truck drivers hitting their tires with a small pipe or club. This may tell you that there is some air in the tire (the club will bounce back if the tire is pressurized—not flat). But doing this will not, in any way, indicate the amount of air pressure in the tire. Sorry, there are no shortcuts. You have to get it weighed correctly.
Consider this Scenario…
Assume you had your coach weighed at each wheel position, drive to heat up the tires, check the chart, set the tire pressure correctly, and shift some stuff to balance your load where needed. Great! A month later, you decide to go on another trip but this time, you are not going to the annual Horseshoe Conference where you helped them build the storage shed. So, you are not going to take your 200-pound horseshoe collection with you and also leave a couple of those big boxes of construction tools at home.
What do you do now? Do you have to go through all that weighing again? No.
Just watch what you remove from the coach and rebalance across an axle by estimating. For example,
- If you removed all that weight from the center of a pass-through storage compartment, rebalancing across the axle may not be needed. However, you should consult the tire chart with your new estimated changes to see if the recommended tire pressure changes.
- If you removed all that weight from one side of the RV (like a side storage compartment typically found hanging below a slide-out), then you need to rebalance.
Shuffle some stuff to the other side while estimating the weight you are moving. If you can’t estimate, use a set of bathroom scales to help you.
Many RVers, especially fulltimers, will change what they carry in their coach during the first couple of years. Anyone that travels regularly in an RV typically will sort out and leave behind the unused stuff they did carry—after all, they really thought it would be used! With any major changes, get the coach weighed again, and rebalance. Your costs will decrease and tires will last longer, plus, it will be safer.
Weighing is offered at many RV rallies and it is not necessary to attend the full rally to get it done. Go in on a day-pass, find the vendor booth, sign up, pay the fee (usually $20.00–$40.00), and be assigned a time to bring in your coach or get in line. The actual weighing is accomplished in about 10–15 minutes. The people will discuss with you the need for rebalancing and show you how to calculate your correct tire pressure settings.
Armed with the correct information, pull over and rebalance your load if needed. If you are overweight, clean out some stuff and leave it behind. Then, drive a distance to heat up the tires, stop, and set your tire pressure correctly.