correct tire pressure? - RV-Dreams Community Forum

The Crumps · RV-Dreams Family Member

correct tire pressure?

53 Merc · RV-Dreams Family Member

Just posted a reply to your other entry. FIND ANOTHER "TIRE GUY" It ain't about mileage or wear. It is about SAFETY for you and your family. Tires under inflated for the load they are carrying will have problems. Find out your ACTUAL weight from scales. Then set your tire pressure at the recommended pressure for the load you are carrying. Do not under-inflate. You probably need the max weight carrying capacity for your application. I am no expert, just a user. To date, I have never changed a flat or blow-out on any RV we have had. (BTW I always have max air pressure in my RV tires) I can't find a smilie for "knock on wood". I am sure I need one.

Roz · RV-Dreams Family Member

53 Merc is correct in that your tire guy gave you incorrect information. The only way to determinyour optimum tire pressure is to have your MH weighed corner by corner. This will indicate if there is too much weight on the roadside or the curbside, front or rear.

Howard and Linda have just becopme a part of RVSEF and are now taking on the job of weighing rigs per individual wheels or duals. Once done, you will have an accurate overall weight, as well as a breakdown on axle by axle and also each end of each axle.

This provides you with important information so you may correct the "balancing of weight" a good bit by moving non-MH items from heavier corners to lighter corners. Once the "best balance" is achieved, you will be provided an optimum tire pressure for your individual coach, as it is loaded.

Likely, Howard can provide a less complicated explanation. Our MH handled better once this was done at Life on Wheels years ago.

Luvglass · RV-Dreams Family Member

The amount of air needed in a tire is totally dependent on the weight being applied to the tire compared to what it's rated to carry. For instance if the tire is rated to carry 3,000 pounds at 80# pressure and you are putting anywhere near that weight on it then you need to be at 80#. If however you are only applying 2500 pounds then you can be at a lower pressure. You can find the recommended pressures at the tire manufacturers websites.

The only way to know how much tire and pressure you need is to weigh your rig on a segmented scale which will give you the weight at each axle. Divide by the number of tires to arrive at the weight on each tire.

As a practical matter, everyone recommends running tires at maximum pressure since all manufacturers use the minimum rated tires they can get away with and more than 50% of rigs that have been weighed are over their GVWR, and actually need bigger tires. Most full timers pretty quickly find this out and switch to higher rated tires when the original set goes.

To know where you are you have to take your rig to a segmented truck scale.

Good luck,

Steve C · RV-Dreams Family Member

Fred,

This note is a little off subject; but, I just wanted to say how much I enjoy your trip journal and hope that Jo will "sharpen her saw" and get more active again soon. I understand that it can become a chore. I'm sure Howard must feel the burn-out from time to time. Love the bird photos and those of the "trip that almost never was..."! RV PAINTER also has a very interesting blog for those of us that enjoy RV-ing and painting. He is a very talented artist with a great, dry wit.

Back on topic. We had a 2010 F450 DRW 4x4 (6) and after 11,000 miles pulling in excess of 18k lbs. found that we had a lot of uneven tread wear of the inside tires on the rear. Can anyone explain this? Would like to avoid that this time around. Ford did replace two of the tires.

Thanks,

Steve

Terry and Jo · RV-Dreams Family Member

With all due respect to Fred (luvglass), I would recommend weighing at each wheel. Simply taking an axle's weight and dividing by two will be somewhat inaccurate. For instance, the roadside wheels on our Mobile Suites carry more weight than the curbside wheels. It may not be a lot, but there could be a possibility of also being overweight on tires.

In our case, I try to put the heaviest weighted items to the curbside inside of the basement. Not only does that better balance the coach, but the basement door on that side is unhampered by a slide over my head, making it easier for me to load and unload items.

Terry

Howard · Host

All major tire manufacturers advise to run the maximum air pressure on the sidewall of the tires OR the tire pressure indicated on your RV's required placard/label UNTIL you can get your RV weighed wheel by wheel.

The location of the label depends on when your motorhome was built. All motorhomes built after June 2, 2008 have been individually weighed by the manufacturer and their federally required weight sticker is located on the inside of the coach near the driver's seat. If built prior to June 2008, the label may be near the driver's seat; if not, it should be in a closet or cabinet somewhere in the coach.

(Trailer labels are located on the exterior on the driver's side near the front or there may be a "secondary" label inside in a cabinet or closet)

If the label has been removed or you can't find it, use the sidewall pressure on the tires - and "yes" that is the maximum "cold" pressure. "Cold" pressure doesn't refer to a particular temperature, just that the vehicle has not yet been driven before the pressure is taken.

As others have said, proper tire inflation is based on the load the tires are carrying, and you can't know that information unless you have the coach weighed by wheel position. Segmented scales and truck stop scales are decent for overall weights, but they are designed to weigh much heavier loads than RVs (a few hundred pounds of discrepancy is not uncommon), and they do not provide loads by wheel position. Dividing an axle weight in half does not provide an accurate reading either. Rarely are RVs perfectly balanced, and many are much heavier on one side than the other.

Once you can find a place to weigh wheel position by wheel position, then you will use the tire charts for your particular tires to determine what pressure to use for the load you are carrying. You use the same air pressure on all tires on the same axle, with the heaviest wheel position determining what pressure to use for that axle. BUT, you never inflate to a pressure higher than the sidewall maximum.

Tires are rated by speed as well, and the load capacity of the tire goes down as speed goes up. But we won't confuse the issue any further with those details here. smile

Underinflation (meaning using a pressure insufficient for the load) is the number one reason for tire failure. Overinflation for the load will result in the center of the tire wearing more quickly and causes less tire contact with the road which can affect steering and braking.

So, until you know how much weight you are carrying on each wheel position, the short answer is to use the sidewall pressure or the RV label pressure. Once weighed, you can adjust if necessary.

NOTE: While the same principals exist for trailers/fifth wheels, because trailer tires tend to "squirm", they have significantly more "lateral load" pressure on the tires. Therefore, it is recommended that trailer tires are run at the maximum sidewall air pressure .... unless trying to resolve a ride quality problem AND the tire charts and load allow a lower pressure.

This information comes from the RV Safety & Education Foundation (RVSEF) website: www.rvsafety.com and from what we've learned from the Executive Director of RVSEF, Walter Cannon.

Jack Mayer · RV-Dreams Family Member

I agree with what Howard said. But I want to "expand" on one area - trailer tires.

Many people, because of lots of tire issues with trailers, run tires that are far over rated for the load they are carrying. Running tires at maximum pressure when you KNOW they are far over rated is not required. In that case, I recommend that the tires be run at a pressure based on the tire charts (plus a little more). In my case, the H rated tires I use (Gooodyear G114's) show on the weight chart that I can run them at 90psi for my total trailer weight (I do not subtract for the pin weight). So I run them at 100psi. Why higher? because I do not know my side-to-side loading, and I know the left side is heavier. Also, I do not subtract the pin weight because dips, bumps and other things can cause a weight shift and cause the load to focus on one or more axles. It is just a safety margin.

Another good example of this is Howards own rig. With his H-rated tires and his relatively light load for those tires I would not run them at max pressure. But you do have to know your weights.

EVERY RV should have individual wheel weights done after you have settled into your "normal" load. And then every few years - since things do change. (And I'm not saying that just because Howard and Linda do weighing now.) You need to have an accurate weight on your RV. If you can not get individual wheel weights, run across a truck scale. It is better than nothing.

The Crumps · RV-Dreams Family Member

I want to thank you all for your help. We will make sure we're at max pressure until we can get each wheel weighed.

We have weighed the RV and we are actually about 2500# under Gross max. We are not collectors/gatherers so I think that helps. Also, we have the tag axle which gives us more capacity.

Even though we are full time we are having to stay near our home town until we finish with some medical stuff, so we haven't put many miles on our RV yet. We travel 100 miles this direction and 100 miles that direction, but always close to home. We put new tires on the RV when we bought it about 9 months ago so I'm sure no damage has been done yet.

Thank you again! Your opinions are what we live by!

Bill and Linda · RV-Dreams Family Member

Howard, as a compliment I say, you have been spending a lot of time with Walter, haven’t you. Outstanding advice and a good follow up from Jack as usual. This 5^th wheel thing is another ball of wax and just to note, trailer tires are “different” than truck tires as to design as they have differing side loads due to be “drug” at times during tight turns. So best to always put tires on trailers that are specifically designed for trailers. That’s also the reason to get a torque wrench and torque the lugs to the proper value. Do this over several hundred miles as the lugs “seat” and they will stay put. You will also be surprised at how many get “looser” as you check them.

A little, gotacha, for pickup truck owners regardless of size: The tire pressure recommend by the manufacture for the truck is the pressure recommended for the full load on the axles of the pickup truck. Do not, IMO, just inflate the tires on the truck, especially the duals, to the maximum tire psi. Unless you are overloading the axles, this is likely too much pressure.

On that note, when you take the truck into a dealer for oil change service, as I did just this morning, they will invariably reset the tire pressure to a lower pressure than the manufacture’s recommend maximum weight pressure. They did it to me this morning. (Probably to improve the ride – I have no idea why, they all seem to do it.) They took my duals down from the 65 psi recommended to 60. I’ve seen them taken down to 55. They even put on the “inspection report” that tire pressure was “reset.” IMO, best to get a quality tire pressure gauge and check the tires yourself.

Howard, now that you are really into this tire and weight thing, perhaps you should recommend a reading of your change to “H” tires on the 5’er. IMO, this change, which I know Jack and others have made on larger 5’er’s, is one of the best safety changes, properly done, you can make. And by the way, I’ve gotten much better mileage and wear from the “H” than I ever got from the “G” tires.

Safe travels

Bill

flyone · RV-Dreams Family Member

After you know your trailer weight, as others have said, set tire pressure for the tire with the most weight on it. Also keep in mind you still need a safety factor--I have read as a rule of thumb the combined capacity of all tires should exceed the loaded trailer weight by 20 percent. Tire pressure can change by as much as (again rule of thumb) 1 psi for every 10 degree temperature change, that goes for ambient temp as well as tire temp. The pressure is to be taken with a cold tire, (not driven on). Tires and recommended tire pressures take all of this into account but it always pays to be safe, give yourself a safty factor on tire inflation.

Flyone