You have heard that to know the proper tire inflation for your tires you must first know the actual weight on your tires. This post will cover the proper procedure for learning your RV’s weight.
The load capacity of your tires is directly proportional to their inflation. More load requires more inflation. Running your tires in overload will do internal structural damage. This damage will be small or even microscopic when they are just a little overweight. But this microscopic damage, in the form of rubber cracks and tears, will only grow as time goes by. Rubber cracks will never “re-form” into the solid rubber structure. These cracks may eventually lead to large separations with the steel belts and tread coming off of the body of the tire, as seen in this example.
This tire took many hundreds or even thousands of miles of flexing with hundreds or even thousands of very small cracks growing. They eventually joined up until the structure of the tire was compromised to the point that it could no longer support the load. Eventually it came apart and probably damaged the RV in the process of disintegration.
If we can minimize and delay the formation and growth of the microscopic cracks, we can add hundreds or even thousands of miles of “life” to our tires. One way we can slow the growth of these cracks is by decreasing the stretching and bending due to the tire structure being overloaded. This means ensuring we have plenty of air pressure to help the tire support the load. But how much pressure do we need? That can be found in the “Load & Inflation” charts published by the tire companies and in industry standards books. Here is an example:
You can clearly see that the load capacity increases with each addition of 5 psi in inflation. Every tire made for highway use has a similar table. You can find links to the tables in THIS blog post.
Learn the load on the tires
So, understanding the importance of having enough inflation for the load, we are left with one problem: Learning the load our RV is placing on our tires.
First, you must “prepare” the RV. Unlike when we get on a scale ourselves when we only wear minimal clothing, the RV needs to be at its heaviest. This means all the tools, books, clothing, and toys we might ever carry. It also means the different fluid containers such as water and propane tanks should be as full as when we travel. With water at 8.4 lbs. per gallon, propane at 4.1 lbs., gasoline at 6 lbs., and diesel at 7 lbs., these fluids can add many hundreds or even a thousand pounds to the load on your tires. If we pull a trailer that adds weight to our hitch, we need to have the trailer loaded and hooked up too. The one exception is if you are pulling a car with four wheels down, aka a “toad,” as the tow bar is only placing a few pounds on the RV, which is not significant.
Objective is to not overload tires
Our objective is to ensure that our tires will not be overloaded in the future. So learning the weight when the RV is heaviest means the rest of the time the tire load will be lighter and less likely to do structural damage to the tires.
Ideally, you can learn the load on each tire position from RVSEF (RV Safety & Education Foundation), which does such weighings at large FMCA conventions and other locations around the country, as listed on their website. Also, Escapees RV club offers tire position weighings. However, you may not be traveling to one of those locations. There are other options such as building supply businesses or sand and gravel pits.
Here are instructions in the form of a worksheet to help you do the calculations required:
Just identify your type of RV, get the scale readings, and after filling in the blanks and doing the arithmetic, you will be able to identify the load on the heavy end of each axle.
Using the heavy-end axle weight, check the information in the Load & Inflation tables for your tires to learn the MINIMUM inflation required for the tires on that axle. The RVIA (RV Industry Association) recommends a +10% margin in load capacity over your GAWR. I recommend adding 10% to the inflation number to minimize the need to add a couple of psi when the temperature changes, which may drop your tire pressure enough to need attention.
In a 7-week, 7,000-mile trip from Ohio to Oregon to Calgary and back a few years ago, I only needed to add a few psi one time, as the rest of the time I was above my minimum and within my +10% margin.
Have a tire question? Ask Roger on his new RV Tires Forum here. It’s hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.