By Roger Marble
I just read another post on a FB page where more incorrect information on tire loads and inflation was published. Soooo, let’s go over this topic again.
Today’s key points: Know the minimum tire inflation based on manufacturer estimates. At a minimum, check your inflation with a good gauge at least monthly and every morning before travel. Better yet: Get, program and use a Tire Pressure Monitor system (TPMS).
Tire inflation seems to be a topic that confuses some and has others believing in misleading or just plain incorrect information. Tire inflation is one item that directly affects the safety of your RV, truck or car as you travel down the highway. Many of my posts have been background information that you really don’t have to know or fully understand. The intent of these topics is to give you a better foundation of understanding more about tires. But if you only pay attention to one series of posts, this is it.
Tires do not carry the load
Tires are just a container of air. It is the inflation air that does the work. Think for a moment of an impact wrench. It can’t do the work of loosening or tightening nuts on your wheels without the air. A tire can’t do the work of carrying the load or provide the traction needed to turn, start or stop if it doesn’t have air. The load a tire can carry is basically based on the air volume of the tire and pressure of that air inside the tire.
If the load was carried by the tire construction, we would have Tire Load and Construction tables. But we don’t. We have Load and Inflation tables because, for a given type and size tire, the load is just a function of air pressure. More pressure gives more load carrying capacity.
If you want to get a feel for how little load your tire can carry without air in it, you can test this yourself. Simply take an unmounted tire and stand on the beads of the tire. I think you will find that the tire can support less than 5% of the rated load before it deflects more than an inch or two.
Some people believe that tires with higher Load Range can carry more load at the same inflation. This is just not correct. You would be hard pressed to measure the uninflated load capacity difference between a Load Range D and E tire or between a G or H Load Range tire because almost any significant load would compress the tire to be flat.
The term Load Range replaced the old “Ply Rating” back in the early ’70s, when tire construction materials became stronger and with the introduction of radial construction.
“Load Range” is marked on your tires
If you are not sure, the “Load Range” is marked on the sidewall of your tires. If you don’t see the words “Load Range” look for “LR” followed by a letter usually between C and G. “Load Range” may not be in large letters, but you should be able to find them on your tires.
TireRack has a good information page on “Load Range” HERE.
The simple answer to how much air you need is on your Certification Label aka Tire Placard that I wrote about last week. Depending on the year your RV was made, this information is on a sticker on the side of your trailer or near the driver’s seat in your Class A. On older RVs it might be glued to the wall inside a cabinet or on the inside of your entry door. Your car or pickup has the sticker on the driver door jamb.
Keep your tire load information handy
Wherever it is, you should also have the information in the stack of owner’s manuals you received when you bought the new RV. Find this data sheet and write down the information for loads, minimum inflation, tire size and load range and place this info where you can easily find it. This inflation is the minimum based on what the RV manufacturer thought you would load into your vehicle. They may have guessed correctly, or you may have gone way over that estimate depending on how much “stuff” you carry.
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.