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I know that tire pressures should be taken when COLD. I had a long quiet time during a drive and got to thinking ... if I start my tires off at 100 psi cold ... when they heat up to 110 psi will they perform as though that 110 psi was the cold pressure? I mean 110 psi is 110 psi right? Will a tire checked in Phoenix at 110 "cold" (which is probably 90 plus ambient) perform the same (carry the same load) as one that is set at 110 psi in Minneapolis where the ambient temp is probably 70 or so?
Is 110 psi the same regardless of the temperature? To me it seems so, but others may actually know. Just curious.
-- Edited by RonC on Saturday 29th of July 2017 03:14:09 PM
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Ron and Janice
2016 Ford F350, King Ranch, DRW, 4x4, CC, 6.7 PS Diesel, remote control air lift system
2017 Durango Gold 381REF, Lambright furniture, MCD shades, morRYDE IS, 8K Disc brakes, GY G114 LR H Tires, 27,320 lbs CGVW
Pressure is dependent upon temperature. P1/T1 = P2/T2. Temperature goes up, Pressure goes up. One problem you are having is thinking there is a great deal of difference between 70° F and 110°F. Gasses live in an absolute temperature world, so the difference would be between 528.9°R and 568.9°R, which means it is a much smaller difference in ambient temperature.
Tire 'cold' pressure ratings are set to allow the pressure as the gas molecules are heated through the friction of tire on road, etc., to increase without causing a problem.
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Barb & Dave O'Keeffe
2002 Alpine 36 MDDS (Figment II), 2018 Ford C-Max HYBRID
Thanks for taking the time to add your expertise to my question. I understand what you've said and agree completely. The reason I'm asking is that my tires (all tires really) are rated to carry a certain load (expressed in pounds) at a specific pressure (no temperature is mentioned). In my case,the tires are rated to carry 3,750 lbs @ 110 psi. If I start the tires out (cold) at 100 psi ... when they heat up and the pressure rises to 110 psi, will they now carry the rated 3,750 lbs?
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Ron and Janice
2016 Ford F350, King Ranch, DRW, 4x4, CC, 6.7 PS Diesel, remote control air lift system
2017 Durango Gold 381REF, Lambright furniture, MCD shades, morRYDE IS, 8K Disc brakes, GY G114 LR H Tires, 27,320 lbs CGVW
Your tires are rated to a specific load at ambient temperature. In your case 3750 lbs when pressure is at 110 psi at 'cold' (or ambient temperature). If you measure in the morning before moving and your tires only register 100 psi, then you need to inflate them to 110 psi in order to carry that load safely at ambient and increased temperature.
Barb
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Barb & Dave O'Keeffe
2002 Alpine 36 MDDS (Figment II), 2018 Ford C-Max HYBRID
Keep in mind in the tire world cold means ambient temperature. In other words, the temp inside the tire matches the outside temp. Having been in the tire industry close to 40 yrs it has always amazed me the misconception of temp, pressures, and loads.
Every tire sold in the US must state maximum load and at what pressure it takes to achieve the stated load. This stated load and pressure is always factored on the width of the intended rim. The is typically a stated rim width for each tire. Changing from the stated width does impact the carrying capacity.
As far as setting pressure, the tire may increase in pressure depending on temp, load, and speed. You may see pressure increases up to 20-25 psi (depending on variables). Tire temps may go as high as 200 degrees (although I wouldn't recommend pushing it that high, slow down and you'll see the temperature drop). Never adjust pressures until the tire is ambient temp. (Usually takes 6-8 hours depending on how it was used, freeway, in town, off road)
A rule of thumb is for every 10 degrees in temp, the tire pressure adjusts one psi.
-- Edited by Rickl on Sunday 30th of July 2017 08:03:45 AM
Tire and wheel manufacturers have factored in the effects of thermal equilibrium (thermal dynamics). A lot of the major tire manufacturers have posted their various tire data books on the internet. Those data books will explain the process and give a ballpark figure for the amount of increase when being operated at road speeds.
