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Old 12-19-2017, 12:10 PM   #15
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Originally Posted by tmw188 View Post
I don't know for sure but I wonder about this CIP cold inflation pressure isn't figured at some typical ambient temperature, like maybe 60-70 degrees perhaps? Checking pressures at fifteen degrees and then topping off and driving south seems like it might end up over inflated. I would probably do the check again the next morning.
Cold inflation pressures are just that.....tire inflated to correct pressure BEFORE driving. Ambient air temperature isn't what your air pressure is based on....it affects the air pressure for sure, but you should ALWAYS set the tire pressure to the correct PSI.... 80, 110, whatever the inflation plaquard tells you, no matter what the ambient temperature is.
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Old 12-20-2017, 09:59 AM   #16
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....not sure I follow all this ...on a "typical" day [72 degrees], I set my front tires at 105-107 to match recommended pressures based on 4-corner/axle weights. Now I will admit up front that I rarely [never] drive in 15 degree temps--sleep in!!!!!. According to my TPMS, if I start out at 105 and 70 degrees, within 20 miles, I am up to appox. 120lbs. If its 50 degree and I start out at 100lbs, they still warm up to approx. 120lbs in a short time. Not sure I fully agree with topping off cold each morning vs monitoring tire ops temps and pressures once underway. Where is the tire-man when you need him??????

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You should not start your day on tires that do not meet at least the minimum inflation needed to support the measured load.
The hot running pressure is not of concern and is not an issue to be concerned with.

As I cover in my blog, I suggest that your daily "target" inflation be your minimum + 10 %. The 10 % margin means you do not have to worry about "topping off" every day as pressure only changes 2% with a 10F change in Ambient so a 50F drop in ambient is unusual.

I have a good number of posts tagged with "Temperature" and or "Inflation," you might review them. I don't expect everyone to remember all the info but I suggest that folks at least read all the posts once, so in the future if they have a tire, wheel, valve, TPMS related question they have some idea of where to go to get the answer.
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Old 12-20-2017, 10:22 AM   #17
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Hmmm...... I check my tire pressures fist thing every Spring. Then maybe again in a couple of months or so. Give them a smack with a hammer occasionally, and for some reason, never had a problem now going on 45 years now.
Good luck, or good tires? People run old tires, underinflated tires or undersize/rated and whine about having tire problems. Get real people, buy good tires, don't let them age out, keep the pressure up and you will be fine.
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Old 12-26-2017, 07:09 PM   #18
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Tire pressure can change with fluctuations in temperature. ... A good estimate to use when comparing tire pressure to air temperature is for every 10 degrees F, tire pressure will adjust by 1 psi. For example, if the outside air temperature increases 10 degrees, the tire pressure will increase by 1 psi.
Tire pressure and temperature | TireBuyer.com
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Old 12-28-2017, 10:29 AM   #19
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Tire pressure changes 1.8% for every 10 degrees (F). Not 1.8 psi, 1.8% of the previous pressure. The difference between setting pressure at 50 F vs 70 F is small, so not worth worrying about unless your psi was barely adequate to begin with. The difference between 70 and 15 is enough to be concerned, even though driving will probably get the tires back to a marginally adequate psi. A soft tire heats up more/faster due to increased sidewall flex, so the same factor that potentially damages it also helps a bit.

If the cold pressure is down 14 psi like sdrtile's is, that's over 12% under inflated, right from the get-go. More than enough to start causing structural damage to the tire when driven. He definite needs to top up the air before driving.

A good strategy is to make the cold inflation measurement on a chilly morning rather than a warm one (if practical). Another is to chose a psi well above the minimum for the load, so that you need not worry if you transition to a colder region and don't get around to adjusting the psi. 10-15% higher inflation than absolutely required is no problem at all. You probably won't even notice the slightly firmer ride.
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Old 12-28-2017, 04:02 PM   #20
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Originally Posted by Gary RVRoamer View Post
Tire pressure changes 1.8% for every 10 degrees (F). Not 1.8 psi, 1.8% of the previous pressure. The difference between setting pressure at 50 F vs 70 F is small, so not worth worrying about unless your psi was barely adequate to begin with. The difference between 70 and 15 is enough to be concerned, even though driving will probably get the tires back to a marginally adequate psi. A soft tire heats up more/faster due to increased sidewall flex, so the same factor that potentially damages it also helps a bit.

If the cold pressure is down 14 psi like sdrtile's is, that's over 12% under inflated, right from the get-go. More than enough to start causing structural damage to the tire when driven. He definite needs to top up the air before driving.

A good strategy is to make the cold inflation measurement on a chilly morning rather than a warm one (if practical). Another is to chose a psi well above the minimum for the load, so that you need not worry if you transition to a colder region and don't get around to adjusting the psi. 10-15% higher inflation than absolutely required is no problem at all. You probably won't even notice the slightly firmer ride.

Yup
I showed the math for the 1.8% in THIS post. To make it easy I suggest folks just think 2%.
Also as I have covered many times I bump my pressure up at least 10% over the min needed so I don't have to chase the inflation every time the temperature changes 20F.

PS I think the 1% comes from an old Tire Rack post. They use to say that as they were thinking of 36 psi Passenger tires. They changed their post after I contacted them.
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