Tire Pressure w/ big Altitude and Temp Swings

[AZRVR17]

At the end of May we are going to start our big 75day summer trip. AZ,CO,SD,WI,MI,WY,ID,UT,AZ. We will be going through some pretty serious changes in altitudes and temp swings. The coach has been corner weighed and I set the pressures off the results 115/85/90. That being said we will be going from 1000 feet to 10,0000 feet and starting off in 100 deg temps and going to where the lows will be in the 30’s or 40’s.

As an example the first weeks looks like this: Scottsdale to Gallup NM through Flagstaff, Gallup to Pagossa Springs through Durango, Pagossa to Creed at the top of Wolf Creek Pass, Granby to SD.

I worry more about under inflation than over in that I can handle a rough ride for a few miles. I ie resetting in Creed and heading down the hill to Denver then to SD.

Thanks in advance for your thoughts and experiences.
JD

[wolfe10]

Altitude has a minor affect on PSI.


Temperature does have a much more significant effect.

[USMCRET]

I have done similar. Just check your pressures each morning and adjust as needed.

[Dutch Star Don]

I would leave them alone. Set the correct temps at home before you leave and enjoy the trip. No need to change for altitude or temp, the tires are designed to work within those parameters. In a single day, some truckers drive from the desert to the snow, they don't adjust.

I check my tires twice a year and adjust the pressure. In between, I watch the pressure via a TPMS unit for any leaks.

[Mike8253]

I was recently at the FMCA Rally in Tucson, and spoke to a Michelin tire engineer about temperature affects on PSI, and if I should adjust or take into account, air temperature and its impact on tire PSI when checking/filling my tires in the morning. He, in no uncertain terms, stated that you should always fill to your required PSI when your tires are "cold", at whatever the ambient temperature is, and before you've driven your rig. Doesn't matter if the OAT is 30 or 80. If you're required PSI is 90, verify or fill to 90 PSI, or whatever your requirement is.

[wolfe10]

Originally Posted by Mike8253

I was recently at the FMCA Rally in Tucson, and spoke to a Michelin tire engineer about temperature affects on PSI, and if I should adjust or take into account, air temperature and its impact on tire PSI when checking/filling my tires in the morning. He, in no uncertain terms, stated that you should always fill to your required PSI when your tires are "cold", at whatever the ambient temperature is, and before you've driven your rig. Doesn't matter if the OAT is 30 or 80. If you're required PSI is 90, verify or fill to 90 PSI, or whatever your requirement is.

CORRECT!


When referring to tire PSI, cold= "at ambient temperature" (be it zero or 100 degrees F) before driving".



Yes, the tire engineers who did the calculations absolutely knew what PSI would do as you drive, expose some tires to the sun, etc.

[Flyer15015]

I live @ 8500' in the Arkansas valley of Colorado and we regularly drive the coach over monarch pass (11.3K) and down to Florida (0') and all I do is put 95# in all 6 tires at the house prior to going either way. Never had an issue.


Mike in Colorado

[GW4607]

Originally Posted by Dutch Star Don

I would leave them alone. Set the correct temps at home before you leave and enjoy the trip. No need to change for altitude or temp, the tires are designed to work within those parameters. In a single day, some truckers drive from the desert to the snow, they don't adjust.

I check my tires twice a year and adjust the pressure. In between, I watch the pressure via a TPMS unit for any leaks.

What he said.

[DutchStarJez]

I had my old Kountry Star for 17 yrs, Michelin's on it the entire time, and did tire pressures exactly as Don describes above. Never had a problem. I will confess that I am a fanatic when it comes to tire repair. Won't do it. Even a small nail gets a new tire in that position. I know I know ---- but peace of mind is worth it IMHO.

[Old-Biscuit]

Check/Adjust tire pressures COLD (in AM prior to being driven on or SUN heating them up)

Regardless of Elevations/daytime temps

[Country Road]

Originally Posted by DutchStarJez

I had my old Kountry Star for 17 yrs, Michelin's on it the entire time, and did tire pressures exactly as Don describes above. Never had a problem. I will confess that I am a fanatic when it comes to tire repair. Won't do it. Even a small nail gets a new tire in that position. I know I know ---- but peace of mind is worth it IMHO.

Wow! That’s a commitment towards safety.

Let me know when you get ready to dump those tires having small nails and maybe we can make a deal. Lol.

[Dutch Star Don]

Just as a side note....I worked for the L.A. County Sheriff for 34 years. The last 16 years I had a County car. It was your responsibility to get it in to the fleet shop for oil changes, tune ups and tire repair. I was amazed at the number of tires being replaced by the fleet people. They never fixed any tires. If a tire went flat on a patrol car, they stuck a new tire and rim on. The flat tires were sent to the fleet headquarters and a new tire was installed on the rim and sent back out to the station. During my time, the majority of these were GoodYear Eagles. The tires were auctioned off and I'm sure made their way back onto the streets.

[AZRVR17]

Thank you for all the comments and thoughts. It never ceases to amaze me how different people address the tire pressure issue. I am probably a little too OCD on the whole issue. I will run at 115/85/90 out of Scottsdale and check/adjust them in Pagossa Springs and any time we are in vastly different climates than last adjusted. Shockingly my Valor TPMS works really well so they are easy to keep an eye on. Thanks again.

[jadatis]

If you fill the tires with best determined pressures for the axles, with a reserve to cover inacuracies in measuring pressure and weight, and unequall weight R/L on the axle, you only have to check, and calculate back to sealevel and average ambiënt temperature .

About height: there is someone who claims that the absolute pressure gives the deflection for a pressure/load relation.
Extreme example , in vacuüm the tire stil has the same deflection with a certain weight and absolute pressure , as when on sealevel 14.7psi ambiënt pressure.

This all at same temperature in and outside tire .

It sounds reasonable to me , because at zero pressure with valve closed, the tire can still carry a 5 to 10% of maximum load. Then absolute pressure in tire is 14,7 psi at sealevel.
When you open the valve, suddenly much less.

This means that at hight, the ambiënt pressure gets lower, say 9.7 psi , and you mesure with a gauge wich measures overpressure above ambiënt pressure, gives 14.7-9.7=5 psi higher.
But tmps sensor sends absolute pressure to the receving unit, wich substracts a fixed 14.7 psi , and still shows the same pressure ( at same temperature)

So if you check your pressures with a gauge on hight, you have to fill that 5 psi higher in the example. Internet shows lists for that hight/ ambiënt pressure relation.
But if you use tmps system to check, you have to do nothing.

Then about the ambiënt temperature.
Everywhere is written, that you have to fill the determined cold pressure at ambiënt temperature whatever it is , freesing 32 degrF or 100degrF on a hot day ( external factors excluded, like sunshine on tire)

But my opinion, concluded from what I was told, that pressure advice is to prevent overheating, when driving at maximum used speed constantly, is that if you fill at sealevel at average ambiënt temperature, or close to it, you can let the cold pressure rise and lower by the ambiënt temperature , and still no overheating, wich is the main goal.

This means that you certainly must not let out air of tire, when you measure 85 psi on a hot morning of 100 degrF in the shade, when determined best pressure is 80 psi. Even if its an E-load tire with 80psi pressure written on it.
Then more deflection so more heatproduction, so change on overheating tire larger. Cooling down of tire is then less then at 70 degrF ( average ambiënt temp, i state but discussable) , because of smaller temperature differences between in and outside tire air and critical temperature of rubber of tire.

On a cold freesing morning of 32 degr better cooling down , so heatproduction of tire can be more , with still no overheating any part of tire.
Then for roadhandling and fuelsaving you may highen up the pressure to that 80 psi in the example, but for savety not needed.

This saves you every time filling up and letting of air everytime on your tripp .

So you measure higher pressure at hight ( at same temperature, with a gauge, and can leave it that way. With tmps it gives same pressure, so you wont worry anyway and dont have to.

And at much different temperature, you measure different pressure, but if its , calculated back to 70 degrF your determined best pressure, also leave it that way.

I made list to search back your fill pressure at average ambiënt temperature( stated as 70 degrF) , and behind it the degrF/ psi different.
Then you can calculate by head howmuch higher or lower the pressure will be. Does not even has to be that acurate.

Here it is
Have a nice long trip, without manically changing the pressure everytime.

37 psi/ 10 F/psi
39 psi/ 10 F/ps
40 psi/ 9,5 F/psi
42 psi/ 9,5 F/psi
43 psi/ 9 F/psi
45 psi/ 9 F/psi
46 psi/ 8,5 F/psi
49 psi/ 8,5 F/psi
50 psi/ 8 F/psi
53 psi/ 8 F/psi
54 psi/ 7,5 F/psi
58 psi/ 7,5 F/psi
59 psi/ 7 F/psi
63 psi/ 7 F/psi
64 psi/ 6,5 F/psi
70 psi/ 6,5 F/psi
71 psi/ 6 F/psi
77 psi/ 6 F/psi
78 psi/ 5,5 F/psi
86 psi/ 5,5 F/psi
87 psi/ 5 F/psi
96 psi/ 5 F/psi
97 psi/ 4,5 F/psi
109 psi/ 4,5 F/psi
110 psi/ 4 F/psi
126 psi/ 4 F/psi
127 psi/ 3,5 F/psi
148 psi/ 3,5 F/psi
149 psi/ 3 F/psi
177 psi/ 3 F/psi