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It would appear that pressure adjustment is warranted if you travel from a warm to a cold or cold to a warm location, or if the temps at your location change drastically. In my neck of the woods, in spring and fall the daily temp. range can vary 30degrees. Since too low pressure is the main concern I'd fill my tires cold at the lowest ambient temp. I expect to drive them in, so long as the resulting warm tire pressures didn't exceed the sidewall limits. Note that the difference in recommended pressure between normal/standard ambient cold inflation temp. (64 to 70deg F) and the recommended pressure at 32F is only 6% or 5lbs in my case. See below: Quote:
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Agree with the first half or your statement. The second half not at all. The PSI on the sidewall is for cold (before driving), and has no relationship to PSI after driving. I promise that the tire engineers are familiar with the Ideal Gas Law and absolutely know what PSI change occurs with increased temperature. I would be surprised if most tires do not exceed the side wall PSI if driven on hot days at highway speeds. |
Though its always needed to determine pressure with a reserve, for savety of tire ( so tire never overheats) the pressure-fluctuation by ambiënt temperature dont need care. If colder , the lower pressure gives more deflection , so more heatproduction a cycle, so at same speed, but also cooling down of tires rubber is better because of more temperature-differences between rubber and in and outside tire air. So rubber still not overheats.
Hotter outside the other way around. So when 100degrF outside, you need higher cold pressure then when 40 degrF outside. The advice pressure is determined for 70 degrF in tire so cold measured also ambiënt temp. I made several lists for pressure/temperature relation, but became to complicated to use. But now I made a simple list, wich is yust as complicated as is needed for the importance of the goal, so read simple. In that list search the pressure you determined to be needed with a reserve, and read behind it the degrF/psi and remember that ( so for every axle , if different pressure, remember the degrF/psi). Then on the road you can calculate by head the needed pressure for cold filling, or when reading tmps pressure while driving, you can calculate acurate enaugh the temperature of the gascompound in the tire. Here it is: 33 psi/ 11 F/psi 34 psi/ 11 F/psi 35 psi/ 10,5 F/psi 36 psi/ 10,5 F/psi 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 |
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Yes you should always inflate tires when they are at Ambient temperature and not warmed from running or being in direct sunlight. Depending on the pressure increase due to driving on tires in NOT CORRECT. In my blog I recommend that the "set pressure" be at least 10% above the minimum pressure needed to support the heaviest load measured on the heaviest loaded tire. |
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You do not need to adjust your tires daily if you have a cushion. Pressure only changes about 2% for each change in ambient temperature of 10F, so having your "set pressure" at +10% you are good for a change in ambient of 50F which normally does not happen every day. TPMS High pressure warning can be at +25% as you should not see that much increase unless running heavy and fast. You do not need to adjust car tire pressure as most have the placard pressure at about +30% based on actual tire loading while RVs are lucky if they are set to +2% based on measured load. |
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So, if they generally see, say (just an example), a ten degree rise, if they start at 30 degrees, they will settle out at 40 degrees. But if they start at 100 degrees, they will settle out at about 110 degrees. another way of seeing this is that the pressure rise from starting pressure will be about the same, regardless of the temperature the tires started at. again, this is a general statement, and other things (like variations in load, direction of sun hitting tires, side winds, etc) will make for some degree of variation from the above statement. |
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Running pressure with no change in Ambient will usually be between +10% and + 20% which assumed the tires are not overloaded and you are not running faster than about 60 MPH AND that you set the "cold" pressure based on actual tire load and used the minimum inflation in the tables + 5% to +10%. Run faster or heavier or not setting the initial pressure correctly will of course affect these numbers. |
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I never move my rig more than ten feet unless I know my tires are above minimum pressure. |
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Brett is 100% correct. I know as I am an actual tire design engineer. |
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Way to involved unless you are in Alaska in the winter and inflating tires when they are warmed indoors. That is not Ambient (Air temperature in the shade) There are similar charts for the military. I think this forum is more concerned for normal highway service in the "lower 48 at temperatures from 0F to 100F AMBIENT. Note a change of ambient of 100 degrees will only result in about a 20% change in tire inflation pressure. That's the reality of the "Gas Law" |
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Nope. Too involved. |
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jadats is Dutch so English is not his first language. He tries hard and does a better job than I would if I had to post in Dutch. Sometimes i think he tries too hard and we end up over complicated. |
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