rvupgradestore.com Composet Products Fridge Defend
RV Life Magazine RV Park Reviews RV Trip Wizard

Author Topic: Another tire pressure question. Sorry.  (Read 713 times)

WannaBeRVing

  • ---
  • Posts: 20
Another tire pressure question. Sorry.
« on: February 25, 2020, 06:39:50 PM »
I know taking care of your tires is crucial and proper pressure is part of that.  Specifically, low pressure is dangerous.  However, I've researched it here and other places and the info can be contradicting.  I feel comfortable that for the TT the proper pressure is that listed on the TT plate.  Or as some suggest, just below that number.

The TV is another story and I'm hoping veterans here can clarify things for me.  I've read that the proper pressure is the recommended pressure listed on the TV plate, and I've read some insist it's the max pressure listed on the tire itself.  All seemingly by those in the know.  So I called Michelin (the maker of my tires) and asked them.  They told me that they recommend the pressure listed on the TV plate and that the number assumes the max payload is being carried.  So I asked them what their max pressure listed on the tire is for.  They said that's there just in case the tires are used in other applications, i.e., different vehicle  with maybe a higher payload.  But it's just that, the max you should ever put in the tire in any situation.

Of course that's different from the other opinion.  Can anyone shed light on the confusion in view of Michelin's statement?

Back2PA

  • Photo moderator
  • ---
  • *
  • Posts: 5740
Re: Another tire pressure question. Sorry.
« Reply #1 on: February 25, 2020, 07:17:11 PM »
The inflation shown on the sidewall is the max load and inflation under any circumstances. The inflation show on the data plate is the inflation for that tire at the manufacturer's max load for the vehicle. If you weigh your vehicle to find the actual tire loading, you can then reference the manufacturer's load and inflation chart to see what inflation you should use for the actual tire loading. On your TV it is likely to be somewhat less than max. On your TT it is likely to be near maximum as TT tires are often loaded to near maximum.
Scott
2014 Montana High Country 343RL (37')
2011 SD F-250 Crewcab LB 4x4, 6.2 Gas, 10K gross
Eezrv TPMS
Fulltimer

donn

  • ---
  • Posts: 3759
Re: Another tire pressure question. Sorry.
« Reply #2 on: February 25, 2020, 07:19:26 PM »
Actually the correct number is....
On the TT ST tires should always be inflated to the max as liated on the tire sidewall.  Generally that is 80PSI.
As for the TV...  again generally speaking tires should be set at the pressure as listed on the placard on the drivers door post.  Depending on the actual load your carrying it could go up from there.  The placard is placed there by the mfg and is calculated to ensure the tires that came OE on the vehicle can support the max load the mfg certifies the vehicle for.

longhaul

  • ---
  • Posts: 523
Re: Another tire pressure question. Sorry.
« Reply #3 on: February 25, 2020, 08:24:46 PM »
  Because of liability issues Michelin can't tell you  to use a different pressure other than the vehicle mfg door tag tire placard recommendations.

 Before the tire placards (mandatory after '06) we used the tire mfg psi for the load charts recommendations...then fined tuned psi determined by the tire tread wear patterns.

  Without knowing anything about your tow vehicle such as its GVWR/FAWR/RAWR....are the tires OEM or higher rated.....or size and load range about all we can tell you is use the tire placard as a starting point. Then adjust psi that helps eliminate odd tread wear such as wearing the tires center.... or both edges.

  I air the rears up when hauling/towing and air the rears down well below the tire placard numbers when running empty.

 EXample; my 2500 Dodge/Cummins tire placard says 50 psi front....80 psi rear on LT265/70/17 LTX A/S load range E.
 The front tires wore the edges fast and the rear rode the centers empty or with 2400 lbs in the bed. I found 65 psi in the fronts and 70 psi in the rear with a max axle load....and 45 psi in the rears when empty gave the best tire wear and ride.

 

 
« Last Edit: February 25, 2020, 08:26:46 PM by longhaul »

grashley

  • ---
  • Posts: 6435
  • Western KY for now.
Re: Another tire pressure question. Sorry.
« Reply #4 on: February 25, 2020, 08:30:10 PM »
I respectfully disagree with donn.  The placards are required by lawyers to show the proper pressure for the vehicle loaded to absolute capacity.  They are the "safe" number, not the ideal number.

The tire sidewall max inflation is correct if the tire is carrying max or near max load.  I prefer tires oversized so they do not have to carry their max load.  The pressure can then be adjusted for the load they actually carry.

On my trunk, (max load 3750# @ 80 psi) running empty, I run 50 psi in front - 2680 # max load and 40 psi in the rear - 2280# max load.  When pulling the FW, I run 60 psi - 3030# in front and 75 psi - 3540# in the rear.  All weights /pressure from the Michelin load and inflation chart.

The empty truck weighs about 4800# on the front axle and 3200# on the rear axle. 
The loaded truck weighs about 5500# on the front axle and 6750# on the rear axle.

Proper lower pressures give better ride and improved tread wear.
Preacher Gordon, DW Debbie
09 Grand Junction 35 TMS  Progressive HW50C
Andersen Ultimate hitch
2013 F350 Lariat LB SRW Supercab diesel 4X4   TST TMS  Garmin 760
Nimrod Series 70 popup (sold)
It's not a dumb question if you do not know the answer.

scottydl

  • Admin assist
  • ---
  • *
  • Posts: 8167
  • Central IL
Re: Another tire pressure question. Sorry.
« Reply #5 on: February 25, 2020, 09:12:49 PM »
^^ Yep. Max pressure on the tow vehicle will safely carry you and the cargo (assuming you are not overloaded), but it's gonna be a ROUGH ride. Adjusting the tire pressure based on the actual weight that each axle/corner bears is how you make sure the tire support is sufficient, and you are getting the best ride possible.

Here's an older thread of mine describing how I went through that "tire math" to figure out the ideal pressures for my Suburban/TV's tires, shorting after buying our trailer.
Scott, wife, 3 boys... and the dog
- 2008 Forest River Wildwood 32BHDS
- 1995 Chevrolet Suburban C2500 tow vehicle
- 1994 Thor Residency motorhome... owned 2007-2012

SpencerPJ

  • ---
  • Posts: 2586
Re: Another tire pressure question. Sorry.
« Reply #6 on: February 26, 2020, 07:05:08 AM »
As you can tell, this is a very subjective topic, almost as bad as 'what oil is best'
I feel that you should run anywhere between what is posted on the TV and the max on the tire.  For me, my TV says 35psi.  Tire max says 43 psi.  I feel if I tow at 35 (in the rear), they are a bit too soft.  I feel taking them to 43 is a bit too hard.  When I tow, I raise my rears to 40 psi, and find the TV does best and a good trade off with all to be considered. 

PS: only be sorry if you have a question and didn't ask  :)).  It's a good question!
2020 F150 Lariat, Max Tow, 3.5 Eco
2012 Puma 21BH TT
Paul & Julie


"Never argue with stupid people. They bring you down to their level and beat you with experience" - Mark Twain

FastEagle

  • ---
  • Posts: 592
Re: Another tire pressure question. Sorry.
« Reply #7 on: February 26, 2020, 08:11:25 AM »
The correct tire inflation pressures for both RV trailer and motorized vehicles are what has been recommended for the original equipment tires and displayed on the vehicle certification label. Deviation may be found on vehicle supplemental labels or in the vehicle owner manual – which the tire loading placard will reference.

Reputable tire dealers or independent tire installers will never recommend inflation pressures below what has been recommended by the vehicle manufacturer. The answer is very simple. By doing so they violate a tire industry safety standard and will be held accountable should that safety violation come to light. 

You might ask; “what is the safety violation”? It’s found in the regulations the vehicle manufacturer must comply with when certifying your vehicle. They are directed to select tires that are appropriate for fitment to that vehicle and then set the appropriate inflation pressures for those tires. Because the FMVSS (standards) are written to insure minimum safety standards are set for that vehicle, the manufacturer’s recommended tire inflation pressures are a minimum standard. That standard is passed on to all subsequent replacement tires by the tire industry caveat; “replacement tires MUST provide a load capacity equal to or greater than the OE tires provided. Of course that is done by setting a new recommended inflation pressure for plus sized tires.

Optional inflation pressures are not often set for RV trailer tire fitments because they seldom have load capacity reserves to draw from so the vehicle manufacturer sets their inflation pressures to maximum tire sidewall pressure. Automotive vehicles almost always have a percentage on inflation pressure available above what has been recommended, because the regulations require them to do that. Options are anything between what has been recommended and tire sidewall max. Most passenger tires do not gain load capacity when going to sidewall max. However, for towing other vehicles, the max pressure will stiffen the passenger sidewalls to help off-set sway from the towed vehicle.
USN RET (PDRL)
DOD RET Journeyman Aircraft Mechanic
SSA RET

Rene T

  • Forum Staff
  • ---
  • *
  • Posts: 15026
  • Every day is payday and every payday I have off
Re: Another tire pressure question. Sorry.
« Reply #8 on: February 26, 2020, 08:20:02 AM »
As you can tell, this is a very subjective topic, almost as bad as 'what oil is best'

Or the best toilet paper.  :o ??? ::) :-\ ;D
Isn't it about time?   (:( (:( (:(
Rene, Lucille & co-pilot Buddy
AKA  Pep N Mem
2011 Chevy Duramax 2500 HD 4X4
2011 Montana High Country 343RL
From the Granite State of NH
& Florida Snowbird in Lakeland FL

Gary RV_Wizard

  • Forum Staff
  • ---
  • *
  • Posts: 69968
  • RVer Emeritus
Re: Another tire pressure question. Sorry.
« Reply #9 on: February 26, 2020, 09:42:45 AM »
I think we have successfully demonstrated but Wannabe complained about - conflicting opinions!  ???


It seems simple enough to me, but you have to be cautious with the wording to avoid confusing folks. Fast Eagle gave an excellent  technical explanation, but I'll paraphrase a bit in hopes of making it even more understandable.

The tire sidewall pressure is the tire manufacturer's specification of the psi required to support the tire's maximum load (weight) rating.  If the tire is actually carrying that much weight, then that is the correct psi to use.   However, if the tire is carrying less weight, it is permissible to use a lower psi, as determined by the tire load-inflation table for that tire size & type.  Note it says "permissible", not "required".

The tire placard is required by federal law to show the vehicle manufacturers psi recommendation for the tires that were supplied with the vehicle (whether trailer or TV or motorhome or car).  The recommendation has to be valid based on the tire manufacturers weight & psi specification, but can take advantage of the permissible lower psi in the load-inflation tables.   That means they can recommend a psi based on their estimate of the actual weight the vehicle may be carrying rather than the maximum weight the tire is capable of carrying.   To keep things simple for the vehicle owner, the vehicle manufacturer typically gives just one recommendation, but multiples are allowed for differing conditions.   Since the vehicle manufacturer has no clue how much weight YOU have in your vehicle at any given time, as a practical matter they have to recommend a psi capable of supporting the vehicle at its designed maximum weight (the vehicle GVWR). They may also specify an optional one for lighter loads, but you rarely see this on consumer-use vehicles anymore.

You, as the owner/operator of the vehicle, have the capability to determine the actual weight on the tires as you actually use/drive the vehicle. You have the option to use those actual weights to select a corresponding psi, which may be less than the vehicle makers recommendation or the tire manufacturers max load spec.  We usually say that is optimizing the tire pressure, meaning selecting the psi that is suitable for the actual weight load on the tire. By optimizing the psi for the actual weight, you may improve ride comfort and tread wear.

Tire shops often inflate tires to the sidewall psi so that they cannot be held liable for under-inflating tires. To use a lesser pressure, they would have to have supporting data, which could be the psi data from the tire placard on the vehicle or it could be an actual scaled weight. Rather than take the time and effort (and possible human errors) to do one of those, they just use the sidewall max load psi.  Occasionally that results in major over-inflation, but none of them have been sued over that [yet].
« Last Edit: February 26, 2020, 09:50:15 AM by Gary RV_Wizard »
Gary
--------------
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

FastEagle

  • ---
  • Posts: 592
Re: Another tire pressure question. Sorry.
« Reply #10 on: February 26, 2020, 03:59:14 PM »


You, as the owner/operator of the vehicle, have the capability to determine the actual weight on the tires as you actually use/drive the vehicle. You have the option to use those actual weights to select a corresponding psi, which may be less than the vehicle makers recommendation or the tire manufacturers max load spec.  We usually say that is optimizing the tire pressure, meaning selecting the psi that is suitable for the actual weight load on the tire. By optimizing the psi for the actual weight, you may improve ride comfort and tread wear.

 [yet].

Inflating tires to the load carried is an acceptable method for commercial vehicles operating under the guidance of FMCSA regulations. Those regulations are not applicable with FMVSS (standards).

However, there is a paragraph on page #44 in the USTMA manual referenced below that gives a procedure for  adjusting tire inflation pressures  to axle loads. But, holding true to the FMVSS guidance, they make a point at the end of the statement to NEVER use inflation pressures below the vehicle manufacturer's recommendations.

https://www.ustires.org/sites/default/files/CareAndService_PassengerAndLightTruckTires.pdf
« Last Edit: February 26, 2020, 04:17:51 PM by FastEagle »
USN RET (PDRL)
DOD RET Journeyman Aircraft Mechanic
SSA RET

longhaul

  • ---
  • Posts: 523
Re: Another tire pressure question. Sorry.
« Reply #11 on: February 27, 2020, 10:01:51 PM »
Quote
The TV is another story and I'm hoping veterans here can clarify things for me.  I've read that the proper pressure is the recommended pressure listed on the TV plate, and I've read some insist it's the max pressure listed on the tire itself.  All seemingly by those in the know.
  People on a forum have various amounts of experience on this subject. Some can have 50 years and hundreds of thousands of miles with various size load carrying vehicles.
 Others only know what they've done with maybe 2-3 trucks.
 Others only know what they read and have very little experience on the subject. They even try to make us think what he/she reads is the only acceptable method.
  The tire placard psi numbers is a recommendation only when were talking about a truck/truck tractor or a pickup truck/suvs/HO vans/etc thats has a high load carrying ability. Vehicles with low load carrying ability can work fine with one psi recommendation.
    Everyone has a opinion.

 Look close at reply #9 from Gary which could be a sticky on any rv website.

MtnGoat

  • ---
  • Posts: 78
Re: Another tire pressure question. Sorry.
« Reply #12 on: February 28, 2020, 12:30:53 AM »
^^ What longhaul said, ^^

       should be a sticky!
USN VN - Aircraft Mech - IT Eng - Ret
2500HD - Springdale 242

John From Detroit

  • ---
  • Posts: 23510
  • ^My New Home^
    • Diabetics Forum
Re: Another tire pressure question. Sorry.
« Reply #13 on: February 28, 2020, 06:51:04 AM »
The proper pressure is determined by putting the loaded RV on a set of scales. one per wheel. and noting the weight that tire is carrying... Then you go to the tire makers's chart.

now the placard weight.. Well that's the RV maker's best guess as to how much "Stuff" you are going to carry around

The "Max Pressure" on the tire..  that's a half truth it says Max Load XXXX pounds at Max Pressure of YYY PSI so if you are carrying the maixmium for that tire (I am) that's the proper pressure.

But if you are not. then the proper pressure is lower.

So the best way is to scale each wheel  THere are instructions for doing that elsewhere on the forum.

Another way is to use parking enforcement chalk across the tire and then drive a SHORT distance.  Notice if the chalk is evenly worn off or if there is still some in the center (Add air) or on the edges (Bleed some off)

But the put 'er on a scale works best.   Buy a Motor Carrier officer a beer and let him scale it for you.

Why is proper inflation important?

well Multiple Reasons: One si maximum tire life.. A tire that is UNDERinflated the sidewealls flex more than they should and this can cause overheating andf KABOOM grade blow out
It alsdo means you have less control as the tire can "Wiggle" more side to side.
And with only the edges of the tread there is less traction surface.

Over in flate and the tire wears in the center only and again there is less traction surface.

So proper inflation is best
Nothing adds excitement like something that is none of your business
My Home is where I park it.

FastEagle

  • ---
  • Posts: 592
Re: Another tire pressure question. Sorry.
« Reply #14 on: February 28, 2020, 08:26:24 AM »
For many years RV trailer owners complained about early tire failures. Probably for as many years consumer groups lobbied NHTSA to provide load capacity reserves, at the least, equal to what was provided to tires in the automotive section. It has never happened. NHTSA just added the caveat; to provide tires they deemed appropriate for that fitment.

Most posters, me included, have always recommended to consumers to use replacement tires with 10 - 20% of load capacity reserves above the vehicle's GAWRs. Finally an origination, RIVA, with some strong influence in the RV trailering manufacturing community stepped in and recommended to all of their members (about 98% of all trailer manufacturer's) to provide at least 10% in load capacity reserves above vehicle certified GAWRs.

RV trailers are notorious for carrying unbalanced loads. The imbalance can be a single wheel position or an entire axle. Tires fitted to the load capacity of the axle in an overloaded condition are going to degrade rapidly and fail. In a catastrophic failure (blowout) on a multiple axle trailer the tire (s) on the same side of the trailer as the failure are very likely to have sustained internal damages as the result of the failure and may also soon fail.

BOTTOM LINE: Do Not inflate your tires to the load carried, unless you're able to do it every time you load up for a move. Even then you may not cover a highly loaded wheel position. Consumers need to be aware of the inflate to load carried as being a commercial trailer procedure not intended for RV trailers. Do yourself a favor and inflate to an inflation pressure that will at least provide the RVIA recommendation or sidewall max if necessary.         
USN RET (PDRL)
DOD RET Journeyman Aircraft Mechanic
SSA RET

Gary RV_Wizard

  • Forum Staff
  • ---
  • *
  • Posts: 69968
  • RVer Emeritus
Re: Another tire pressure question. Sorry.
« Reply #15 on: February 28, 2020, 10:28:04 AM »
Obviously loads can change, so perhaps we should say that tires should be inflated to the peak load they will carry rather than the exact actual load at the moment. Ambient temperatures change too, and the set pressure should allow for temperature changes between the now and the next pressure update. A little extra never hurts, but a little shy can hurt badly.

The psi's shown in the inflation tables are the minimum psi needed for the stated load weight. Adding some extra psi makes sure you have enough if the weight increases or the temperature drops before your next cold tire check. If you only check pressures once in awhile, make sure you have a wide safety margin. If you check weight and psi daily, you can work in a much narrower range.
Gary
--------------
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

WannaBeRVing

  • ---
  • Posts: 20
Re: Another tire pressure question. Sorry.
« Reply #16 on: February 28, 2020, 07:30:08 PM »
Some good info here.  (Yeah, still contradicting, but I now better understand it all)  Thanks to all.

Now about that toilet paper.  Which do you folks recommend? 

Just kidding.


longhaul

  • ---
  • Posts: 523
Re: Another tire pressure question. Sorry.
« Reply #17 on: February 29, 2020, 09:17:54 PM »
Some are throwing trailer tire pressure input in the mix ...when you asked about tire pressure for your truck. Gotta' read between the lines on some comments.

 Oh yeah..I use 2 ply TP.  :D