How do I set inflation on my tow vehicle and RV tires?

RV Tire Safety
with RV tire expert Roger Marble

Got this PM from someone who reads RV forums:

Good evening. I’m looking for some professional advice. I have a 2500HD pulling a fifth wheel, my steer axle is 4,000 lbs., drive axle is 5,380 lbs., and our trailer is 7,700 lbs. Tires on the TV are rated for 3,100 lbs. apiece at 80 psi. The RV tires are rated for 2,800 lbs. at 80 psi.

Do you think I am OK to run 65 psi in the steer axle and 70 psi in the drive axle? What I’ve been doing is 75 psi steer, 75-80 psi drive, and 80 psi trailer. Our TV tires are Michelin MS2 LT265/70-17. The load range chart says I can run much less psi. Also, our trailer tires are Maxxis 8008 225/75-15 LR E. Also, the load range chart shows I can run less psi.

Any thoughts on what you would do would greatly be appreciated. Thank you. —New Crusader owner

Answer:
To start with, it is important to remember that we should never operate tires with inflation lower than what is needed to support the actual load on the tires.

As I have pointed out in my blog, we first need to confirm the actual load on our tires. For TV we will find the side-to-side loading is usually 49/51 to 50/50 split, so we can take the measured axle loads, divide by 2, and then use the resulting figure when consulting the Load Inflation tables for our size tire.

I have links to many load/inflation tables and related info HERE. Once you find the MINIMUM inflation, I suggest you add at least 10% to that number to allow for day-to-day variations. Having said this, it is important to remember that the car company spent a lot of time and money evaluating many different tires at different pressures to arrive at the recommendation that is on the Tire Placard on the driver door jam. You should note that the Placard inflation may be higher than my above-suggested calculation, as my calculation is only addressing load and not handling, braking or the fuel economy.

The scale weight for the TV for the above needs to be the reading with the RV and TV fully loaded as heavy as you ever expect to tow.

The RV tire inflation is different. Due to SIDE LOADING in trailer application, I strongly recommend running the tire sidewall inflation as your CIP (cold inflation pressure). I think that if you review the RV Placard info from the RV company, you will also find that they say to use the inflation number on the tire sidewall.

I know you were hoping I would just tell you to run xx psi here and yy there and zz on the trailer, but without knowing tire sizes and Load Range for all your tires, I don’t have enough info to provide an informed answer. But I feel you now have enough info that after reading the sidewalls of your tires (be sure to check each as they might be different on TV and RV and possibly even different front and rear on the TV), you now know how to establish the correct inflation for your current vehicles and for any vehicles you own in the future.

I hope this information and these instructions help. If not, you can always contact me directly at tireman9 (at) gmail.com .

Read more from Roger Marble on his blog at RVtiresafety.net.

 ##RVT845

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2 Thoughts to “How do I set inflation on my tow vehicle and RV tires?”

  1. Travilenman

    It is simply amazing what kind & rated tires RV manufactures will put on the axels of what they build….I run ST225-15Lr=E @70# for my 5200# axels on the RV. 60# 0n front TV & 75 on rear axel..TV tires are LT245r16LrE.. This seems to work out very well….I weigh my set-up overtime when I leave on a trip….Those highway weigh stations come in handy…USE THEM…they don’t cost a dime and you have a good idea of what you weigh…

  2. Fletcher Christian

    You talk all the time about tire pressures and load ratings. The tires that came with my RV were under rated for the weight of the RV, so I replaced them with tires rated for the weight of my RV. Problem solved? Wrong. One day at a routine restroom stop for the dogs, I noticed a low tire, so I called Good Sam Roadside Assistance to have spare put on. The tech that came out to change tires had soapy water and checked tire for leak. No leaks, so he checked the rim and found a 4 inch crack in the rim. After arrival at destination, I cleaned off the rim looking for numbers to find a matching rim and found the weight rating for the rim. Multiplying that number times 4 equaled total weight rating 2,000 lbs. below weight of RV. So please advise your readers to not only check weight rating of tires, but check weight ratings of rims also. My situation could have been disastrous if I had not found the low tire at a potty break.

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