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Old 10-25-2011, 06:34 AM   #1
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High altitude tire pressure

Should there be changes in tire pressure at high altitude? I have been at 8500 ft and 2300 ft in the last few days. Where should I adjust the tire pressure? My sleep number bed has had to be adjusted every night. Should tire pressures change enough to be concerned?
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Old 10-25-2011, 07:29 AM   #2
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Assuming you didn't air the tires to maximum inflation while you stopped in the lowest part of Death Valley you're okay.
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Old 10-25-2011, 08:20 AM   #3
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Good Question, Central Tire Safety Resources Link

Quote:
Originally Posted by okmunky View Post
Should there be changes in tire pressure at high altitude? I have been at 8500 ft and 2300 ft in the last few days...
Were we driving the same trip? Santa Fe and ABQ Balloon Fiesta?

That sounds silly to other readers, I know; but, man, you should have seen all the rigs out there! It was like the biggest rally you've ever seen...

Coming out of N. Texas and arriving in Santa Fe, I noticed my tire pressures wandering, whereas they are normally steady. Several tires were 2-4 psi low. Was this due to the altitude? If so, why were some affected, and others not?

First, the gage is measuring a differential. So, the tires should read the same, between seashore and mountains, assuming temperatures don't vary too much.

Out there, I was probably seeing temperature variations: for each 10F drop you'll see 1-2psi less on the gage, say the experts. Then, with chilly nights and bright morning sun, pressures quickly diverge when some tires are warmed by the sun and others aren't. The pressures in your manufacturers' tables are based on 60F temperature. If you wish to be ultra-precise, set 1 psi less per 10F difference under 60F and the reverse for above that temperature: inflating at a tire & outside temp of 30F when the manufacturer calls for 85psi at a given axle-end weight, we'd make sure the gage reads 82psi. Then, as the tires roll along and warm up, they should hit 85psi as the temperature climbs through 60F enroute to a normal operating temperature of 120F.

There are lots of myths among RV'ers about tire pressure, the most common of which is, there is a one-pressure-fits-all axiom for their rigs. My daddy said always keep 110 psi in the steering wheels, and 100 in the duals.

The second seems to be, following the guidance from the vehicle certification placard/label behind the driver's seat.

Adhering to either could result in disaster; but, more likely than not, it'll just hand you a rougher ride, a little smaller footprint on the road, premature wear.




HERE is a place from which you can access numerous tire safety publications by both the govt and the industry.
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Old 10-25-2011, 11:12 AM   #4
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A tire is so close to being a rigid container that the pressure changes very little with altitude.
I think the Michelin web sire addresses the issue and as I recall the change going from sea level to over 5000 feet was within the accuracy tolerance of most gauges.
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Old 10-25-2011, 03:41 PM   #5
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okmunky, your tire pressure will be OK,...much ado about nothing.

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Old 10-25-2011, 04:02 PM   #6
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Went from 8142' at Conway Summit in California (near Mono Lake) to -236' at Death Valley in one day. No problems with the tires, but it sure was hard on a half empty bottle of water:
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Old 10-25-2011, 04:14 PM   #7
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You ought to see a styrofoam cup that has been taken down to 100 feet under water.
It is a perfect little cup about two inches or so tall.
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Old 10-25-2011, 11:38 PM   #8
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For every 1000 feet of altitude there will be a 0.48 psi change in pressure.

For every 10 degrees F of temperature there will be a 2 percent change in pressure.

Now consider that when you go higher in altitude you will typically see a decrease in temperature and an increase in altitude would also provide a 0.48 psi change. So do some math and they may just about cancel out.

At 80 psi a 2 percent change in tire pressure would be about 1.6 psi, so now you would be running at about 78 (working a lower temperature change) psi. At the same time say you went down about 6000 feet so that is a 2.8 psi increase. So now that would put you at 81.2 or 81 psi.

Personally I never run at extreme max or minimum but I do run a happy medium based on the weight of the vehicle. So unless you are running the max/min the difference is not going to affect you very much. That would be assuming that your max pressure for your tire is above 80 psi, and the minimum is below psi, so strike a happy medium of say 85 max, and 75 min based on your weight and you are still within the manufacturer's recommendation for tire inflation.

Tireman9 posts on this forum and the FMCA forum. He has a blog that can be found here with good information in it.

Tireman Blog

And his blog for Tire Pressure

Note: There are many who state that there is 1 degree of pressure change for each 10 degrees of temperature. Well, for passenger cars running 35 psi a 2 percent change is 0.7 psi for 10 degrees F change. However, run that tire up to 110 psi and a 2 percent change is 2 psi. So if you do the math for 2 percent for every 10 degrees, read RV Tire manuals, you'll have the right numbers.
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Old 10-25-2011, 11:51 PM   #9
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Quote:
Originally Posted by vermilye View Post
Went from 8142' at Conway Summit in California (near Mono Lake) to -236' at Death Valley in one day. No problems with the tires, but it sure was hard on a half empty bottle of water:
We did the opposite, went from almost sea level to Yellowstone. Had one bag of potato chips explode and another one was ready to. Others in the group found bottles leaking and sealed single use camera bags ready to explode.
But it won't make much if any difference to tires.
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Old 10-26-2011, 01:02 AM   #10
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I set mine at home (360 feet) before going on a trip and leave them alone the entire time even for trips across the country through a wide range of altitudes and temps.

I check them with an IR gun every stop and check pressures based on large temp changes between tires. A hotter tire indicates low pressure.

A little study I did:

================================================== =
Tire air pressure at various altitudes has been discussed before and I decided to check it on my rig during a three week trip to Arizona.

I measured before we left and when we returned as well as when we were at a higher altitude.

I used an Accutire Oniprog gauge accurate +/- 1% 0 to 99lb. About $18.00

Guage was at room temperature of the coach about 68 degrees.

Measured after coach had not moved for 48 hours.

Michelin XRV 235/ 80R 22.5 tires with about 28,000 miles on them.

DATE TEMP LOCATION ALTITUDE DF PF DRO DRI PRO PRI

1/06/08 54 CLOVIS CA 335' 96.4 95.4 90.0 90.2 90.6 90.2

1/19/08 61 BENSON AZ 4,350' 98.9 EEE 92.6 93.3 EEE 93.1

1/26/08 57 CLOVIS CA 335' 96.0 94.3 88.9 90.1 89.9 89.2


EEE SUN WAS ON THE TIRE AND METER WON'T DISPLAY OVER 99 POUNDS

DF DRIVER FRONT
PF PASSENGER FRONT
DRO DRIVER REAR OUTER DUAL
DRI DRIVER REAR INNER DUAL
PRO PASSENGER REAR OUTER DUAL
PRI PASSENGER REAR INNER DUAL
TEMP OUTSIDE TEMPERATURE
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Old 10-26-2011, 07:05 AM   #11
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You don't need a formula - just a tire pressure gauge. Check the tire pressure and adjust if needed to stay within the range for your tire. It's probably fine, though, a the others have already shown.
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Old 10-26-2011, 07:50 AM   #12
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Quote:
Originally Posted by Wayne M View Post

For every 10 degrees F of temperature there will be a 2 percent change in pressure.


Personally I never run at extreme max or minimum but I do run a happy medium based on the weight of the vehicle. So unless you are running the max/min the difference is not going to affect you very much. That would be assuming that your max pressure for your tire is above 80 psi, and the minimum is below psi, so strike a happy medium of say 85 max, and 75 min based on your weight and you are still within the manufacturer's recommendation for tire inflation.

Tireman9 posts on this forum and the FMCA forum. He has a blog that can be found here with good information in it.

Tireman Blog
I like the 2% even better. On our jets, maintenance has a chart they apply to pressure stds when the temp is below/above std (60F).

Hey, Tireman hints that the manufacturer's numbers are minimums; it begs the question: Are the numbers in the table the least pressure you should have, or the ideal pressure?

It is the latter.

All this discussion is OCD, trivial, until you are the one having the blowout! The NM police allowed my buddy Ronnie one last kiss on his DW's forehead before they zipped up the bag (non-MH mishap). This is not going to happen to me, if I can help it.
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Old 10-30-2011, 01:12 AM   #13
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Quote:
Originally Posted by dieselclacker View Post
okmunky, your tire pressure will be OK,...much ado about nothing.

Dieselclacker
Good to know. Thanks everyone!
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Old 10-30-2011, 10:41 AM   #14
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The make up of the tire itself can, and does, have a consequence in all this, sidewall rigidity specifically.

The modern tire, especially larger ones, have strong sidewalls, as compared to old bias type tires, so difference in outside pressure due to elevation is less noticeable (for want of a better word).


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