RV Tire Safety
with RV tire expert Roger Marble
As trailer owners start applying the new Goodyear Endurance ST tire, many are discovering that for some sizes the Endurance tire is only available in a Load Range that is higher than their OE tires. Some are concerned about what inflation to run. I have even seen some claim that running an LR-E at LR-D inflation, i.e., not at 80 but at 65, that the “tire will be overloaded, heat up and fail.”
While I understand some of the confusion, I do not agree with some of the concern or replies.
Tire load capacity is a function of the tire size and inflation level as long as you stay in the same “type” tire. By “type” I mean P type, or LT type, or ST type, or for large RVs, “truck” type.
If you stay with the same type and use the same numeric “size” then the only thing left to change is the Load Range or “Ply Rating.” While I do not like using Ply Rating as it is an old and discontinued nomenclature, it may help for better understanding in this post for you to think of the old term.
Important Point. “It is the air pressure that supports the load NOT the Ply Rating.” This statement is supported for every tire made by every tire company in the world through the use of Load and Inflation tables. These tables show a size and then for different levels of inflation the load capacity of that tire when inflated to that level. You will never see a tire shown where an LR-D at, say, 65 psi can support 1,500 pounds and for the same size the same tire when having an LR-E rating shown a higher load capacity at 65 psi. Not even just 1 pound more.
So an LR-E can support the same load at 50 psi as an LR-C, or the same load at 65 psi as an LR-D at 65.
You will not be overloading the LR-E if you load it to the 65 psi rating shown for that type and size tire and inflate it to 65 psi as you would for an LR-D. Since you are not overloading the LR-E tire it is not going to overheat at 65 psi with the 65 psi load, so the LR-E tire is not going to “overheat” at 65 psi any more than the LR-D will “overheat” if it is loaded to the 50 psi load rating and inflated to 50 psi.
When going to a higher “Ply Rating” you can then increase the CIP which increases the tire Load Capacity, which means it will actually be running cooler because of the greater “Margin.” The higher inflation will also lower the Interply Shear, which may lead to longer tire life.
When making the change you do need to confirm the upper inflation level for the rim. The wheel manufacturer should provide that information. As an alternative, the wheel will have a max load capacity stated. Looking at the OE tire size that comes on that wheel, look for the inflation that corresponds to that load and I would consider that to be the wheel inflation rating.
Read more from Roger Marble on his blog at RVtiresafety.net.
I need a little help understanding exactly what CIP to set my Goodyear Endurance tires to. I have ST235/80R16 load range E. I recently had my tires weighed individually – axle 1 2962 and 2890, axle 2 3040 and 2875. The tag on the 5th wheel says CIP to 80. Should I run the tires at 80, or adjust each to the next higher PSI on the chart? This would put 3 tires at 65 and one at 70 PSI. Would it be OK to set all four tires at 70?
CY, A couple of important points. 1. You have a multi-axle trailer. As I have covered in my posts and on my RVTireSafety blog. that type of suspension increases the “Shear” forces on the tire belts that are trying to tear the tire apart. You can lower these forces a bit by running higher pressure. This post was aimed at those who discovered that Goodyear Endurance is only available in a Load Range that was higher than the OE tires. In your case that is not the situation. Your OE tires were LR-E with an RV company recommended 80 psi CIP. You have confirmed you will need at least 65 to 70 psi at a minimum to support the measured load. I also have suggested many times to use at least +10% over the minimum needed to support the load. I have also covered the industry recommendation to run all tires on an axle at the same pressure. So there are a number of reasons for you to set your CIP to 80 psi on all 4 trailer tires.
Thank you Roger. That’s what I was running, but with multiple pieces of information I wasn’t positive. You cleared up my confusion. Again, THANK YOU!
I’ve been inflating my tires to the max psi shown on the sidewall for years. Both trailer and tow vehicle. Am I doing something wrong? I’ve only had one tire failure in 25 years of RV’ing.
Tommy without more details I would suggest you inflate the tow vehicle tires to the tire placard on the tow vehicle. 2. Inflate the trailer tires to the inflation on the trailer.
These recommendations assume you are running the OE size and Load Range tires. You can learn more by reading the posts on my blog.
It is a bit confusing, as in his previous post he says that if you have a tandem axle trailer, you should probably inflate the tires those multiple axle trailers to their sidewall indicated maximum cold psi to lessen shear and premature tire failure. But you are correct that having tires inflated to 80 psi to carry a 50 or 60 psi load will stress the trailer structure a lot more.
Will. If you have changed tire size or Load range you have to do some work. There is no one answer that fits all the different questions that get asked. I have posted answers for people that have changed just the Load Range and for people who have changed the size and load range. I have answered questions for people with lightweight single axle trailers and with heavy multi-axle trailers. Also answered questions from Motorhome owners. Each of these situations needs a slightly different approach.
For the best tire life, I do suggest that multi-axle trailers run a higher than OE level of inflation if the tire load capacity has been changed. BUT for most trailers, the tire applied by the RV company is near the limit for load capacity and should probably have its load capacity increased. If you can fit a larger tire than you may be able to provide more load capacity without needing to increase the inflation above the OE level. I have dozens of posts both specific and general on how to select inflation for trailer application so maybe the best thing to do is to see what I have already written on the topic. If you still have questions you can contact me directly by email. The address is posted under my picture on my blog.
While this is pretty much true, other aspects should be taken into consideration. Over inflating a tire for the load that is put on it then can easily cause increased suspension wear and Vehicle or TT structural stresses that decrease their life. A tire has a lot to perform beyond just carrying the load. A proper footprint for maximum braking and handling is provided by running the proper PSI for the load. Too high of PSI in the tire for the load on it can negatively affect tire contact with the road. The tire also has to compliment the suspension by absorbing some road shock. What it doesn’t is transmitted to the vehicle or trailer itself. Too high of pressure for the load can cause some structural damage to the tire itself by road shock since there is not the proper amount of “give” to allow the tire to flex as it should.
Get the tire maker load/pressure chart and inflate to the level of what load you are typically putting on your individual trailer axles. The tire maker put in the R&D on the tire and is the best source to determine what pressure to run. Take the guess work and potential error out of the equation and let the tire maker’s load pressure chart do all the problem solving. You paid for the tires, so get your money’s worth.
I generally agree with what you said. You will notice I did not tell the person asking the original question to run the LR-E 80 psi. His situation was a bit unusual but there are a number of others who will also discover that the size for their trailer only is available in higher Load Ratings than the OE tires if they switch to Goodyear Endurance tires.