Should there be different pressure in each tire? Well, it is a reasonable question given the fact that we tire folks tell owners of motorhomes to get “4-corner weights,” especially if you have a Class A. But the quick answer is no, you do not need different inflation for each tire. The proper inflation for all the tires on any axle is at least as much as the pressure needed for the heaviest tire position on that axle.
Now, let’s be sure we all understand what I am talking about. “4-corner weighing” means learning the weight of each tire position on your RV, i.e., RF, LF, RR and LR. For most motorhomes the rear positions have “dual” tires, which mean two tires, side by side, on each end of the rear axle. Note I said “tire position,” not each tire. The Load & Inflation tables give the minimum inflation for “single” or front tire position and a different inflation for the tires in a “dual” application. So we do not need to weigh each individual tire as we know that when properly matched by OD, a pair of tires in a dual position have essentially equal loading on each tire.
I can hear some asking about large Class A’s that have a “tag” axle. Yes, you need to get the load on the tire on each end of your “tag,” so you will be getting the load on 6 tire positions.
Where to get weighed
Here is a YouTube video of one RV getting weights from RVSEF at an FMCA Convention. Select Conventions here for more information.
Now, not everyone will be able to get to an FMCA Convention, but you can get “4-corner weight” at some Escapees events. It is also possible to learn your weight for each tire position and use this FORM to help you do the math.
Learning the actual corner weights is important as some large RVs have discovered a side-to-side unbalance of 1,000 lbs. That means some tires will be operating in overload and the driver will not know it until maybe they have a tire failure.
Smaller RVs can probably get away with just learning the weight on each axle with the RV and TV loaded to its heaviest, and this can be done at Truck Scales.
Then calculate 51% or 52% for each axle, and then use that weight number to confirm you are not exceeding the load capacity of the tires. However, this is not a substitute for learning individual tire position loads at least once in the life of your RV.
Weights for towables
For towables, including 5ers, your calculated heavy weight should be no more than 90% of the tire capacity when inflated per the Load & Inflation tables. So you may need to adjust your cold inflation or move some of your “stuff” around to get a better balance of loading.
This estimate of 52% of the axle weight is not as good to use on heavier Class A RVs as the double or triple slides and residential refrigerators and large volume fuel or holding tanks can easily exceed a couple of percent side-to-side imbalance.
Your dry weight is not important when we are talking about tire loading. The GAWR (Gross Axle Weight Rating) is just a number 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 can’t average the axle weight to learn the max weight on the heavier loaded tire.
CAT scales are not designed or intended to be used to get one side of an axle weight, and to do so is against CAT policy. But some people have found local gravel pits or grain silo operations that can do one end of an axle and with that information, you can use the form above to do your own calculation. Once you learn your 4-corner weights you will know if you need to move some stuff around to get a better balance, or change inflation, or even off-load some stuff to avoid overloading your tires.
After getting my Class C 4-corner weights, I knew I was within 2% of being in balance. I still get on a CAT scale every year or so and confirm my individual axle weights have not crept up. If I ever discover an axle weight is significantly different on a CAT scale from the total for the ends of that axle with my 4-corner weighing, I know I need to take some action.
Have a tire question? Ask Roger on his RV Tires Forum here. It’s hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.
Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.
We have found ALL classes of RVs can have the imbalance/overloading problem. In fact, the smaller RVs are easier, and no less likely, to overload because of the lower Occupant and Cargo Carring Capacity. (OCCC)
Admittedly I don’t have knowledge of all TPM systems only the system I had on my former motor home which had one setting for all tires. Do other systems have the capability to monitor individual corners?
The best tire pressure monitoring system would monitor and report each individual tire pressure. However, the most basic system could give warning if any monitored tire lost pressure requiring all tires to be inspected when low pressure was detected. In the case of dual tires, it is important to keep both properly inflated as if one tire’s pressure loss is 20-percent or more, it is a run flat and should be dismounted and inspected, not just aired up. The other tire will potentially be over loaded next to a low or flat tire.
I posted a question a week ago to Roger about tire pressure. No response. What gives?
Hi, Tom. Don’t feel bad. I asked him a question a few days ago but haven’t heard back either. 😉 He’s been tied up presenting many seminars at the FMCA Convention in Perry, GA, this week. So, once he’s done with that he’ll probably get back to you. Have a great day. 😀 –Diane at RVtravel.com