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Old 05-14-2016, 10:30 AM   #1
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Tire pressure?

My tires are at the correct cold pressure now, but a 20-degree drop expected overnight. So psi will be naturally going down. Will I need to air them up before leaving early in the morning or will they be okay until the rising daytime temps bring them back up? Thanks.
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Old 05-14-2016, 10:42 AM   #2
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My tires are at the correct cold pressure now, but a 20-degree drop expected overnight. So psi will be naturally going down. Will I need to air them up before leaving early in the morning or will they be okay until the rising daytime temps bring them back up? Thanks.
I have always struggled with the issue. I bring my 5er home in the afternoon load it and check air pressures in the tires. In the morning I get up and several pounds low but after hitting the road within a few miles the pressure is up to and above the 80psi requirements. Don't know if it is right or wrong but I don't add air in the morning if few pounds low.

PS I have have been checking torque on the 5er tires and have found them low several times.
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Old 05-14-2016, 10:46 AM   #3
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I believe all manufacturers instructions for checking and setting tire pressure indicates to do it in the 'morning' before tempurature has risen.
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Old 05-14-2016, 10:47 AM   #4
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My tires are at the correct cold pressure now, but a 20-degree drop expected overnight. So psi will be naturally going down. Will I need to air them up before leaving early in the morning or will they be okay until the rising daytime temps bring them back up? Thanks.
You can really drive yourself crazy with this, especially if you have a TPMS. Cold pressure means cold starting pressure. They never want less that that pressure in the tire when it rolls. Frankly I don't know why they don't just say "minimum pressure?" It needs to be high enough to minimize sidewall flex when starting out. I keep my cold pressure according to the spec for something like 50 degrees. If it is higher when the weather warms up, it should be fine as long as it never goes above the high pressure limit on my tires. I have a class A so I shoot for 90 pounds at 55 degrees or so and never get beyond 105 on the road on a warm day.
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Old 05-14-2016, 10:55 AM   #5
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I have a 5er and use the max side wall pressure to get the max loading on the tires. Since I'm around 2500 lbs below gross a few pounds low in the morning should be fine. Just another way to justify not having to add air on colder then normal morning but if you are worry about it going down the road piece of mind is worth a lot. I do have TST and the pressure can go up 10 pounds on warm day from what it was in the morning.
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Old 05-14-2016, 10:57 AM   #6
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TP

I asked a local tire guy the same question and he replyed that as soon as you drive about 5 miles the road friction on the tires causes heat bringing your tires right back to pressure. Not a bad idea to drive it and then check the pressure too.
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Old 05-14-2016, 11:27 AM   #7
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Thanks to all for quick and intelligent replies. Indeed a tricky question. My tires are 14-inch Maxxis with 50 psi min. Think I'll make sure they are at least 48 before leaving in morning. FYI: When I checked them while hot yesterday they were at 54. Don't know what the max would be, but worrying less after hearing from you guys.
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Old 05-14-2016, 05:42 PM   #8
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for savety of the tires it is probably OK to leave the cold pressure at the lower pressure at colder outside temp.
For reasons of fuel saving and stiffer tires you can give same pressure as you determined to be right for normal outside temp.

For savety counts that no piece of rubber of tire goes above a sertain temp, I estimate that on 130 degr C/265 degr F.
there has to be a temp difference between rubber and inside tire air to cool the rubber , and a difference in temp between inside tire and outside tire temp to give the heat energy over from inside tire to outside tire .
The higher the temp differences the better cooling down.

When colder outside tire temp , there is more temp difference between in and outside tire temp and rubber/inside tire temp, so more heatenergy can be transported.

Because of the lower pressure when cold , the tire deflects more, and so produces more heat.
But probably this is exactly in line with the more cooling down because of the more temp differences, so no part of rubber goes over 265 degr F at wich rubber hardens and damages, so still save for the tires.
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Old 05-14-2016, 05:54 PM   #9
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Best to measure in the morning and inflate to max. regardless if one morning it is 50 degrees and the next morning it's 30 degrees. I would not run them low regardless of if it is only for 5 miles. JMHO.
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Old 05-14-2016, 05:57 PM   #10
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I inflate to the stamped 65 PSI when the tires are "cold" or normal ambient temperature.

Yes that PSI will go up after I start towing but that is normal so I do not worry about it.
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