Tire pressures...again!

[garysfb]

Well in the final analysis there are two things that proper air pressures accomplish. Tire wear and safety, and a comfortable ride. They are sometimes at odds with each other. But at the end of the day we're only talking about 5-10 pounds of difference in the result of whatever method you use. I'm comfortable with my decision.

And by the way, thanks to everyone for your insight and input.

[RVPioneer]

Originally Posted by drwaynesmith

Truth dies in silence.

You are correct. We can’t just let incorrect, inaccurate or misinformed statements hang out there for everyone to read. It will breed more ignorance.

[Msmoto]

There is a range of correct pressures. The lower number is specified by some manufacturers as the psi vs load. This is the minimum. However, the maximum on the sidewall may be several psi higher.
With my last Airstream I changed to 16” wheels, ran light truck tires and the pressure per manufacturer was near 50 psi. I ran about 55 psi to stiffen the ride and reduce side wind wander. This was about ten psi less than the standard 65 suggested by Airstream with 15” wheels. The result was a lot less rivet popping (a phenomenon well known to Airstreamers).
In my LTV, the slightly higher pressures reduce movement in side winds.
The tire pressures in vehicles is just one component off the suspension which includes spring rate, shock absorbers and anti-sway bars. Tuning one’s suspension takes all into account and results in a much more pleasant RV experience.

[jadatis]

Originally Posted by Msmoto

Truck/RV tires drop about 2 psi per 10 degrees Fahrenheit in ambient temperature. However, once you begin driving when it is 20 degrees they will warm up quickly to normal operating temperature and be inflated properly.

https://www.fleetequipmentmag.com/un...-air-pressure/

That article confirms what I wrote in my post # 52 , so to my idea its certainly no nonsense.
Only addition I give is that at 20 degr F. you dont need to heighten up for safety of tires, but may do so for roadhandling.
And maybe at extreme high ambiënt temps ,the balance between heating up and cooling down is gone, and you even have to fill a higher "cold " pressure ( simply when temp in- and out-side the tire is the same, and that mostly is when not driven for hours.) then the fi 120psi it gives when going from 65 or 70 degr F.
You can discuss which temperature is the right one, but that advice cold is given for a temperature is no question.



I would like to know Tireman9''s opinion about that article.
I think also he dont think its noncence.

[RVPioneer]

^^^Read post #87.

He corrects the misstatement in the article that tire pressure drops 2psi with each 10F degree drop in temperature, with the statement that it drops 2% for each 10F degree drop. He also advises against the use of warming up a tire by driving at speed to obtain correct pressure as the proper method to set tire pressure.

In post #48, he informs us that the idea of “cold” being 70F, as proposed in the technorv article is incorrect.

This thread alone, demonstrates that statements can be found to support any idea. Finding such statements doesn’t make the idea correct.

[jadatis]

I was refering to the posts # 91 to # 93 in wich the article was called dangerously misleading and wrong.


read the article back, and I forgive them the writing 2 psi instead 2% error.

[RVPioneer]

Originally Posted by jadatis

I was refering to the posts # 91 to # 93 in wich the article was called dangerously misleading and wrong.


read the article back, and I forgive them the writing 2 psi instead 2% error.

With luck, he’ll be along to reiterate what he’s said. In the mean time, he’s posted enough on this thread, that it should be pretty straightforward to determine where he stands on setting correct tire pressure and the methods used to do so.

[mike5511]

Originally Posted by garysfb

When I first posted several weeks ago I had no idea how much ego, emotion and testosterone would come into play. And way too much time spent on a fairly simple concept. Tireman you rock, common sense mixed with facts and experience.

So following the KISS method here is my takeaway. Weight the coach fully loaded for a trip including fuel, DEF and water, self and DW. Determine pressures based on tire manufacturers chart. Add 10 percent, but not to exceed tire manufacturers max pressure's based on max loads. Check pressures prior to departure and don't worry about a few pounds low because of the 10 percent cushion. Maybe in extremely hot ambiant temp bleed off a couple pounds, but that in my experience would be rare. And you're done.

Once pressures have been set, all you do is check the TPMS and go. Simple!

That is my take as well. (unless big temp extremes are encountered) Surprised nobody has mentioned the pressure changes relative to elevation.

[Tireman9]

Originally Posted by Msmoto

I check my pressures at about 60 degrees in a heated garage during winter travel, but run slightly higher pressures than given by RV data. In my LTV, cold, ambient pressures are 63/65 f/r. In summer these are checked with ambient temp of from 70 - 80 degrees as garage is not air conditioned but I will go 64/66 if at 80 degrees. I like to look at tire manufacturers data based on load, then ad about 10 % for additional safety factor but never exceeding or actually coming close to maximum pressures on sidewall.

Hope this relieves any anxiety.... LOL

Oh, BTW, I have checked tire temps with IR thermometer, especially from side to side to detect other issues. When I used to run tire pressure monitors on my Class A Moho, I think I saw temps of 120 as cold pressures were I believe as high as 110 psi.

Note the pressure molded on the tire sidewall is actually the Minimum needed to support the Maximum load. You can confirm by looking at the numbers in the tables.

[Tireman9]

Originally Posted by KanzKran

From the article: "Those load/inflation tables are all based on an ambient temperature of 70 degrees F."

I've seen mention of tables being based on 70F ambient, but for the life of me, I don't see how that's in any way relevant. If it takes 100 psi to support the load with the tire shape and contact patch the tire manufacturer designed for at a particular load, why would it make any difference what the temperature is?

If it's 0F ambient when setting out, it takes 100 psi (a made up number). If it's 90F first thing in the morning, it still takes 100 psi. You may have to adjust the pressure before departing after a big temperature swing. That's common for me as I leave snow country one day and am in south Florida or Texas two days later, and especially vice-versa where I have to air up in the morning.

But why are inflation tables 'based on 70F ambient', and what difference does that make? Or is that just something the author misunderstood?

Also from the article: "Having said that, you need to be aware that cold weather can create a different challenge. As an example, a tire that has cooled down after running all day and measures 100 PSI at 70 degrees F will lose pressure if it sits out overnight and the temperature drops to 20 degrees F. When the tire is checked, you will find only 90 PSI in the tire because when the temperature drops, so does the tire pressure. Every loss of 10 degrees F equals a loss of two PSI. You may think that the tire is underinflated but is not. As soon as it warms back up to 70 degrees F, the tire pressure will be back to the specified 100 PSI."

That author seems to be suggesting running at inadequate pressure while it warms up. Or maybe that if you delay departure until it warms up, it'll be where it needs to be. I can't quite figure out what Mr. Cohn is saying here. Regardless, if my pressure get too close to the 100% table values for my axle loads, they get air before departing, but it takes a pretty good ambient swing, as I air them to 110% normally.

Ambient IS NOT 70°F. I have contacted the author and publisher of that incorrect information.

[RVPioneer]

Originally Posted by mike5511

That is my take as well. (unless big temp extremes are encountered) Surprised nobody has mentioned the pressure changes relative to elevation.

That’s been discussed.

[wolfe10]

Originally Posted by RVPioneer

That’s been discussed.

The answer being that it is NOT a significant factor. Real world experience in our coach supports that as well.


We live at 27' above sea level. We often summer in Angel Fire, NM at 8,750'. Temperature IS a relevant factor. Elevation/altitude not so much!

[jadatis]

To use an exagerated example ,to make it clear.
Say at a certain altitude the ambiënt pressure is 5 psi lower then on sealevel ,so 14.7 - 5 = 9.7 psi.
Then if on sealevel 100 psi is needed, then on that altitude you have to measure 105 psi.
Once read that the absolute pressure gives the deflection, and that sounded reasonable to me.

So yust as for temperature, then dont lower to 100 psi.

[Tireman9]

I have also talked with Eric at TecnoRV about ambient not being any specific temperature. He seemed to understand the issue. Don't know if/when he will update his video.


Pressure is really simple.
Pressure shown in the tables is the minimum the tire needs to support the stated load when the tires are "cold". "Cold" means the tires are not warmed up from being driven on or in direct Sunlight for the preceding 2 - 3 hours. With the exception of people who are checking pressure indoors with either heat or A/C, this "COLD" means at the Ambient temperature, which is the prevailing air temperature. So the only correct time to check air pressure is when the tire is at the outdoor air temperature, before you start driving and before it gets warmed up by the Sun..


Don't know how to make this clearer.