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Old 06-14-2017, 02:16 PM   #1
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What is correct tire pressure to inflate tow vehicle

An Airstream dealer advised me to use the pressures on the drivers door for correct tire pressures, 35 PSI, even though the Max inflation on my Dynapro 275 55/R20 113T have a Max inflation pressure on the tire at 51 PSI. I have a Ford Expedition 2016.
Other forums seem to indicate that for full loads applied to the tow vehicle while towing, you should increase the tire pressure according to the manufacturer's load charts. We are about to embark on our maiden voyage soon and would appreciate your thoughts.
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Old 06-14-2017, 02:32 PM   #2
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The absolute best way to determine optimal tire pressure is to use a digital optical thermometer - the hand held point and click type available for about $20. Start with what you think is an appropriate pressure then drive the vehicle for several miles at road speeds then pull over and check temperatures on the inner and outer edges and the center of the tire tread.
If the center is hotter than the edges, reduce the pressure. If the edges are hotter add pressure to even it out. It will take a little experimentation to get the hang of it but you will in fact know you have the best pressure for tire wear and safety.
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Old 06-14-2017, 02:39 PM   #3
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Start by weighing the trailer and use a tire inflation chart for your size tires.

http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

The above is an interesting follow up but not a starting point
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Old 06-15-2017, 06:28 AM   #4
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I would never remove or add air once under way unless the tire was grossly under inflated. I have never seen a tire pressure spec other than cold inflation. Meaning before the tire has been used. Adding or removing air after the start of a trip is a guess. You asked the question what is correct not what is a guess. The correct pressure is one matched to the load. Find out what is the load and inflate the tire pressure to that spec.

The tire pressure listed on the decal for any vehicle is not given for a vehicle set up to tow. That data if given by the vehicle manufacture would be listed in the owners manual. And to be more accurate would be to weigh the load and inflate tires to that load when the tires are cold.

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Old 06-15-2017, 06:43 AM   #5
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In the owner's manual for my truck (2017 Sierra) it states that the recommended tire pressure on the door sticker is the minimum pressure required to carry the maximum rated load. When towing, I inflate each tire 3-4 lbs. above what the door sticker states, which is still well under the 44psi maximum listed on the tire. I'm carrying under the maximum rated load, and so far the tire wear is even and the ride is good and stable, and I haven't noted any tires being overheated when we stop to for fuel or to take a break.
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Old 06-15-2017, 07:43 AM   #6
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"I would never remove or add air once under way unless the tire was grossly under inflated. I have never seen a tire pressure spec other than cold inflation. Meaning before the tire has been used. Adding or removing air after the start of a trip is a guess. You asked the question what is correct not what is a guess. The correct pressure is one matched to the load. Find out what is the load and inflate the tire pressure to that spec."

The method you suggest is using an engineer's best guess. Checking temperature is the real world. Adjusting air pressures as needed hot or cold has never been a problem that I've experienced. Of course, you need to keep in mind that pressure will increase slightly when hot.
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Old 06-15-2017, 02:48 PM   #7
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The door sticker pressures are for optimum comfort and control without a load. Most of us load the rear tires to the max with trailer wt and gear. I always run my rear tires at full inflation (44 psig) but I adjust the front pressure to give me good foot print and braking/steering control. For me that is 35 psig. These pressures give me cool running tires except on 90 degree days when the pavement is hot and transferring heat to the treads
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Old 06-16-2017, 06:35 AM   #8
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Quote:
Originally Posted by JCWDCW View Post
The door sticker pressures are for optimum comfort and control without a load. .......
Ah ..... Mmmmmm ........ Not exactly.

The pressure listed on the vehicle tire placard is for the fully loaded vehicle (unless stated otherwise, and even then, there will be 2 pressures, and one of those will be for fully loaded.)
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Old 06-16-2017, 06:38 AM   #9
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Originally Posted by CapriRacer View Post
Ah ..... Mmmmmm ........ Not exactly.

The pressure listed on the vehicle tire placard is for the fully loaded vehicle (unless stated otherwise, and even then, there will be 2 pressures, and one of those will be for fully loaded.)

Speaking as a vehicle manufacturer's rep, this is correct. The pressures for each axle are stated for the full GAWR of each axle. You would never need to increase pressure above the door jamb label....unless you are overloading either axle...then I'm going to scold you, for other vehicle durability and/or safety reasons.
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Old 06-16-2017, 07:30 AM   #10
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I set up a family members F150 to tow their 25' AS (heavy tongue weight). At the door jam tire pressure the truck squished all over the place. Pumped the Passenger tires up to the max sidewall pressure (44 psi) and the truck was solid thereafter. I am not going to dispute what was said above but these are real world results that worked!
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Old 06-17-2017, 09:51 AM   #11
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Originally Posted by crispyboy View Post
I set up a family members F150 to tow their 25' AS (heavy tongue weight). At the door jam tire pressure the truck squished all over the place. Pumped the Passenger tires up to the max sidewall pressure (44 psi) and the truck was solid thereafter. I am not going to dispute what was said above but these are real world results that worked!
My Take exactly! My Dakota does say the 35psi pressures are for 3800 lbs load on rear axles; 3100 on front. Curb Weight is 4226 Lbs. Max payload is 1784 lbs. I can tell you that when Pep Boys dropped my tire pressures to 35 all round (unknown to me) the rear tires ran hot with normal load for shuttling back and forth to Texas; no trailer, and definitely no more than 1000 lbs including me and my wife. Finally got the pressure up to 44 and everything was cool....and stable. The tire says max load at 44 psig, but that is for nearly half the curb weight of my vehicle on one tire. No matter what the door sticker says, real world experience says more pressure is good under full load. As noted several times in this thread, tire temps tell the story and adjusting pressure to keep the tires running cool is the proper solution.
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Old 06-17-2017, 10:10 AM   #12
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Originally Posted by crispyboy View Post
I set up a family members F150 to tow their 25' AS (heavy tongue weight). At the door jam tire pressure the truck squished all over the place. Pumped the Passenger tires up to the max sidewall pressure (44 psi) and the truck was solid thereafter. I am not going to dispute what was said above but these are real world results that worked!


Real world is using a certified scale.
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Old 06-18-2017, 01:06 PM   #13
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Real world is using a certified scale.
I do not like being snippy but really! How does a "Real World" Certified scale that tells me I'm not over loaded per the door stickers specs explain how I'm still running hot tires at door sticker 35 psig. Dry weight on rear wheels is about 2100Lbs. Full load is 3800. Leaves 1700 Lbs load less 350# for us and the dog... I know I can't load 1400+ lbs in the 5 Ft box; I just don't have that much weight in clothes, lawn chairs and sundries. So per the Door sticker I'm under the max loaded axle weight...at 35psig...still running HOT rear tires.

Scales have their place in setting up a TV and trailer where you are not sure of your numbers and for tweaking the set-up. For me, I will set pressures that work...always have. Not only about load, but about getting a solid footprint on the pavement that doesn't wear the treads unevenly Middle or Outsides. Door stickers don't even think about that kind of rational
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Old 06-26-2017, 07:14 PM   #14
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Individual wheel weights are the gold standard.

Loads can be different at either end of the axle (a certainty with the trailer). That's step one with correct tire pressure per axle. Heaviest load determines. High or low isn't good.

Knowing the absolute minimum for TV tires (tested for steady state pressure rise; TT tires are to sidewall maximum) is where one leaves tires alone to then test WD. Static and dynamic.

Suspensions aren't tuned via tire pressure. It's as lousy (and lazy) a default position as a WDH being "good enough" with fender measurements.

WD will have a range of adjustments to work within. Know them.

And scale use is most of all a numerical baseline. A reference.

Problems come up. Lack of reference points makes for near impossible diagnosis. Different TV tires are a classic case of, "what's wrong with my rig?" Have to eliminate before one can speculate.

And scale use as an annual check that all is as before.

"Real world" is how those of us in transportation keep a check on what's happening with a rig. Legal issues. Wear issues. Safety issues. Machines break. Tires distort. The scale (the context) may be different, but not the principle.

Scales are easy to find and use. 24/7/365 when near an Interstate. Not at all like 45-50 years ago.

Even phone apps nowadays.

Try it.

.
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Old 06-26-2017, 07:50 PM   #15
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I've been looking into exactly the same question.

Load range 113 tires, which the OP has, hit their max weight capacity at 35 PSI. Increasing beyond 35 does NOT increase load carrying capacity. The spec for this is a standard and all manufacturers use it. The standard does not even list weight capacity over 35 PSI. I have not found a tire manufacturer or other pro oriented site that recommended or gave reasons for running tires over the vehicle manufacturers recommended inflation pressure.
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Old 06-27-2017, 06:30 AM   #16
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I spent 5 years as the technical rep to Ford for a major tire manufacturer. I worked along side of people who called on GM, Toyota, etc.

They all do it the same way. They do handling tests on everything they make - every model car and every model truck, both empty and fully loaded at the pressure listed on the vehicle tire placard. They know from experience that there is a small difference between tire manufacturers at a given pressure and that pressure matters much more than brand. They will request changes in the tire to get the feel that they want, but these are minor tweaks. Plus they will also report to their management if the vehicle is doing odd things (in other words, needs sway, spring rate and/or shock changes.)

And the big thing I learned about this testing is that they did not deviate from the pressure listed on the vehicle tire placard - and they only approved a vehicle for production if it didn't do anything unpredictable.

So I would be very careful deviating from what the vehicle tire placard says.
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Old 06-27-2017, 07:25 AM   #17
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"And the big thing I learned about this testing is that they did not deviate from the pressure listed on the vehicle tire placard - and they only approved a vehicle for production if it didn't do anything unpredictable.

So I would be very careful deviating from what the vehicle tire placard says."

Not "doing anything unpredictable" is a far cry from optimizing tire / vehicle performance. Think about it.
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Old 06-27-2017, 08:39 AM   #18
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Not "doing anything unpredictable" is a far cry from optimizing tire / vehicle performance. Think about it.
And the question posed by the thread starter ....... what is the correct pressure? If there are any questions as to what is the correct pressure, the placard pressure would be the answer. If an owner wants to deviate from that pressure that person owns the vehicle and has a right to run the tires over inflated, under inflated or flat. That person owns the vehicle.

With that said, any given vehicle manufacturer has spent at least tens of thousands of dollars (if not more) and thousands of hours designing, manufacturing and testing on any assembly to bring a product to market. Not that the vehicle is perfect and not that the vehicle pin points an experience for every owner's need, every time on every operation.

However if some one is asking the general question, "We are about to embark on our maiden voyage soon and would appreciate your thoughts?" The answer is at least start at the place the vehicle manufacturer that designed the vehicle recommends. I have seen far more damage, wear and tear created to a vehicle by the owner changing from the manufacturers specs than I have seen by sticking with the specs.

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Old 06-28-2017, 06:59 AM   #19
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And the question posed by the thread starter ....... what is the correct pressure? If there are any questions as to what is the correct pressure, the placard pressure would be the answer. If an owner wants to deviate from that pressure that person owns the vehicle and has a right to run the tires over inflated, under inflated or flat. That person owns the vehicle.

With that said, any given vehicle manufacturer has spent at least tens of thousands of dollars (if not more) and thousands of hours designing, manufacturing and testing on any assembly to bring a product to market. Not that the vehicle is perfect and not that the vehicle pin points an experience for every owner's need, every time on every operation.

However if some one is asking the general question, "We are about to embark on our maiden voyage soon and would appreciate your thoughts?" The answer is at least start at the place the vehicle manufacturer that designed the vehicle recommends. I have seen far more damage, wear and tear created to a vehicle by the owner changing from the manufacturers specs than I have seen by sticking with the specs.

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I agree completely that the pressures listed by the vehicle supplier are GENERALLY acceptable and will get you there. The pressures the manufacturer suggests are not highly sophisticated engineering calculations for each make / model as you state.
The CORRECT pressure is one that is adjusted for the load and is best discovered by checking the temperatures across the tire tread and adjusting the pressure accordingly.
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Old 06-28-2017, 07:14 AM   #20
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I agree completely that the pressures listed by the vehicle supplier are GENERALLY acceptable and will get you there. The pressures the manufacturer suggests are not highly sophisticated engineering calculations for each make / model as you state.
The CORRECT pressure is one that is adjusted for the load and is best discovered by checking the temperatures across the tire tread and adjusting the pressure accordingly.
Here's the problem, John. To my knowledge, no one has ever done a full on handling test at different inflation pressures than those listed on the vehicle tire placard - unlike the vehicle manufacturers who not only do full on tests, but do them repeatedly with different evaluators driving. Without doing a full on handling test - one that destroys the tires - one can't be sure if the vehicle behaves benignly or not.

Nowadays, even before the first vehicle is tested, there is a computer simulation that is used to optimize things and look for potential problem areas. These computer simulations have been in use for over 30 years and are now quite accurate - to the point that Formula 1 teams (and others) use them to set up their vehicles - then verify that set up once the track is available.

I think that qualifies as highly sophisticated engineering calculations.
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