Last week I got a reply to my post on “Is the tire pressure too high?” A longtime RVtravel.com reader said: “‘Confirm the max load on each tire will never exceed the load capability for your cold psi per the published tables.’ I’ll bet very few readers have any way to weigh individual tires to check this. I sure don’t.”
How to get RV weighed
To the question of “how” to get the weights, I suggest you check an FMCA convention or an Escapees event to see if they will be offering the weighing service at their event. I have seen some state scales in Oregon that leave their truck scales “on” so you can collect the weight information there. You can check your state. I have used the scale at a local “sand & gravel” business. Some people have contacted their state police to learn where they are doing truck weighing. RVSEF offers the service across the U.S., so you can contact them. Here’s a video from RVSEF showing the procedure.
Yes, learning the actual load or weight on each tire is not always easy, but you don’t need to check each tire each travel day or even each week or month. Here is what I have done.
What is “4 corner weight”?
First we need to all be talking with the same understanding of what “4 corner weight” is. This is usually about large Class A motorhomes. The data shows that some number of those units can be significantly (1,000# or more) unbalanced side-to-side on an axle. What we are looking for is learning the actual load on each individual tire. If you think about vehicle weight, you will realize that a tire on the driver’s side does not completely share the load with the tire on the passenger side of a vehicle. There may be some sharing, but it is probably less than a few percentage points.
To learn the weight we are talking about, you need to load your RV to the heaviest you ever expect to be. Remember, we are trying to protect against the “worst case”.
Smaller RVs, those under 25′, can probably get away with just learning the weight on each axle with the RV loaded to its heaviest. Then calculate 52% for each axle, and then use that weight number to confirm you are not exceeding the load capacity of the tires.
Heavy weight for towables
For towables, including fifth wheels, your calculated heavy weight should be no more than 90% of the tire capacity when inflated per the Load & Inflation tables. I covered the reason for this 90% limit in my blog posts on Interply Shear. The RVIA (see that Gold sticker near the door on the trailer) has a requirement that tire capacity should be equal to 110% of GAWR (Gross Axle Weight Rating).
The max load capacity for a tire is the load in pounds shown on the tire.
Your dry weight is not important when we are talking about tire loading. The GAWR is the total weight for all the tires on any one axle. The tire on the passenger side has no idea what the load on the driver side is, so you really can’t average the axle weight to learn the max weight on the heavier loaded tire.
Tire “dual” loading
“Dual” loading is when two tires are mounted side by side on one end of an axle, as we see on the rear of most Class A and Class C motorhomes, and you have on “dually” pickup trucks like your F450. Dual does not apply to RV trailers. LT (light truck) and Commercial truck tires do have different load capacities if mounted on the front (single) or mounted on the rear (dual).
Side note: You do not need fresh water and holding tanks full. Think of your loading when you start a trip. Fresh water is normally full—so is propane, gas or diesel, and food pantry—but holding tanks are empty. And don’t forget your toolbox. That would be what I would call “heaviest expected weight.”
This is when you get on a truck scale and get readings with just one axle on each scale pad. You may need a couple of readings depending on pad spacing and your axle locations. If towing, you should get both trailer and truck weights as you should also confirm you are not overloading your tow vehicle tires, either. There are many YouTube videos on weighing RVs.
Example
Suppose you have tires that say 3,900# @ 80 psi. Your GAWR on the certification label is 7,000#. RVIA requires the tires have a capacity of 110% of the 7,000#, or 7,700# total, or 3,850# each. So you might think you are OK. But if your RV axle is “out of balance” side-to-side by 1%, or 3,885# on the heavy end, you would have a tire in overload. Not a great deal, but in overload assuming the scale is accurate +/- 1% and you have a 100% accurate pressure gauge. What if your axle is unbalanced by 200# or 300#? Tow vehicles are normally more balanced, so just take the axle load and divide by the number of tires on that axle.
The RVIA 110% requirement went into effect in November 2018. So there are many RVs out there that only require that tires be capable of supporting 100% of GAWR, so that 10% “cushion” is gone.
Recommended load capacity requirement
I strongly support the RVIA’s 110% load capacity requirement. In fact, my Interply Shear data suggests that something closer to 125% would be desirable. But the RV companies simply have not designed their vehicles with large enough wheel wells to allow that large of a tire even if the cost penalty was less than $200 an RV.
Back to your original question: You do not need to learn the individual loads on each tire position. BUT I do suggest you assume at least a 2% out-of-balance and apply that to the weight reading you can get at truck scales. (You just need to pay attention to where each axle is on which scale pad.)
Help with calculations
HERE is a worksheet and information to help with the calculations. (It is a PDF, so hopefully you can download it to your device from that link.)
Final note. You do not need to be checking your “4 corner weights” every trip. Get it done once and after you have adjusted your loading you should be good for a long time unless you add some major weight items like switching to granite counter tops. I got my 4 corner weights measured in 2020 and all I do is get regular CAT scale readings once a year to guard against unknown “weight creep”.
Roger Marble
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If you have tire questions, check out Roger’s Blog as well as his posts on RVtravel.com. There are hundreds of posts covering everything to do with tires.
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Roger, we do weighing for RVSEF and we find side to side imbalance in all classes of RVs, Class A, B, and C motorhomes, diesel and gas, travel trailers, fifth wheels, and truck campers. I would say 2% is pretty normal, 5% is not unusual, and occasionally 10% or more. That also applies to tow vehicles, a heavy toolbox or other heavy item in the bed of a pickup truck can create an unbalanced condition fairly easily.
Thank you, Roger! We last were 4-corner weighed at Spartan RV Chassis while attending a 3-day training session on our RV chassis in June 2023. Although underweight both then and a year earlier when 4-corner weighed at the Newmar international rally, our side-to-side weight distribution difference was lower and within spec. Happy new year and safe travels! 🙂