The following question about tire Load Range is from an RV Forum on trailers.
Originally posted by NavyL:
If the trailer came with Load Range D tires from the factory, and you replace them with Load Range E tires – I just don’t see the need to run the Load Range E tires at the full 80 psi. Tire manufacturers have inflation pressure vs. weight charts for a reason.
My reply regarding tire Load Range:
If you change from LR-D to LR-E (or from LR-C to LR-D), you will only get an increase in load capacity, or an increase in the Reserve Load, if you run higher than the Certification Sticker inflation psi. If you look at the Load & Inflation tables (they are almost all identical for ST- and LT-type tires) and look at your actual scale weights, you can calculate your current Reserve Load and see what inflation you would need to get to a Reserve closer to 20% or 25%. Due to the unique forces (“Interply Shear“) tires must tolerate on multi-axle trailers, I and other tire engineers suggest at least a 15% Reserve with 20% being better. On my personal RV I run 20 to 25% Reserve Load.
Keep a record of your tires’ information
While we are talking about the certification label, I advise people to snap a picture of the label, or labels if more than one, along with a shot of the complete tire size and Load Range info on your tires, PLUS the full DOT serial including the data code portion of the DOT serial. That way if the printing on the sticker fades or your tire gets cut and destroys itself, you have a record so you can file a claim if you purchased “Road Hazard” warranty on your tires, as I have. Plus you have the info if you need to check against a tire recall notice, you can answer the question of what size and Load Range you are currently running. Keep a picture of the Weight Slip too. It’s a lot easier to have all this tire-related info in one place on your phone.
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.
Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.
This is one time when Roger’s reply has me still in the dark, with no real answer. i always thought you went with MFG psi that is on the side of the tire.
Sorry, but the inflation number on the tire sidewall is the cold inflation necessary to support the load number on that tire. Tire companies do not know the weight of the RV tire is going on. Tire companies do follow the published Load & Inflation chart information. RV MFG is required to select a tire size and specify the inflation for the tires necessary to support the GAWR. GAWR is not to be exceeded. BUT a majority of RVs that have been weighed by RVSEF has been found to be overweight so this means that a large number of tires in RV usage are overweight. The above facts are why I and other tire engineers advise RV owners to learn the actual weight on the tires, consult the tables and select the necessary minimum inflation and add a bit more air so you have a Reserve Load. HERE are a few posts from my blog that cover this concept in more detail and gives examples of some measurements and calculations.
I have a hard time comprehending what you say and I worked with spec’s and numbers all my life. I had to buy tires for my dump trailer with a higher load range. The type of tire and load range that came with the trailer wasn’t available anywhere this past summer. I just inflate them to the manufactures specification. But you also need to check that your tire rims can handle the increase air pressure.
Totally agree. Roger has got me pointed the right direction most times, but only because it tells me to go to the manufacturers charts!
In this case, what does the psi on the vehicles Certification sticker have to with the new higher rated tire (“, if you run higher than the Certification Sticker inflation psi.”)???
Weigh the vehicle properly, calculate the correct PSI from the new tire’s chart, and inflate accordingly. Whats the sticker have to do with anything at that point?
Yes, it can be confusing. BUT the Certification Sticker information is required by law to provide tire size and the minimum cold inflation necessary to support the stated GAWR. The problem comes when people put more “stuff” in the RV, exceed the GAWR and the result is overloaded tires which then can turn into failed tires.
If you check my replies above, and follow the links you can find much more information.
Roger, I very much enjoyed your presentations at the FMCA Rally in Tucson. Almost overloaded with information. Keep up the excellent work. See you in Perry, 2023.