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Old 09-14-2015, 09:14 AM   #1
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Cold tire pressure

The manufacturer says 80 pound cold temperature. So the outside temperature is 75 degrees and the tire pressure is 80 pounds. In the morning it is 59 degrees and the tire pressure is 78 pounds. So what cold temperature does the manufacturer have in mind? It does get confusing......
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Old 09-14-2015, 09:44 AM   #2
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Its not the ambient temp. Its the Tire temp which changes with use.

TMI Follows: https://en.wikipedia.org/wiki/Cold_inflation_pressure

Good luck.
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Old 09-14-2015, 09:45 AM   #3
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Generally, when they are talking about 'cold tire' pressure, they are referring to the fact that the vehicle has not moved and that the 'tires' are cold. The tires heat up after being driven due to friction on the road. While outside temps could effect tire pressure, you should only see that with extreme cold.
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Old 09-14-2015, 10:29 AM   #4
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"Cold" means has not been driven on for at least a couple hours. Set the pressure at whatever the ambient is at the time you are going to use the vehicle.

Tire pressure changes a bit less than 2% with each 10 degrees of temperature change. That would be about 1.5 lbs on your 80 psi base pressure. You could adjust it every day if the weather changes, but the smart way is to either put in a few extra psi (on a hot day), or always check/fill in the cool of the early morning hours. Either way, you will then have plenty of pressure to cover the daily temperature swings (typically about 20 degrees).

If you fill the tires in the winter in Florida and then drive north to Minnesota, re-check the pressure as you go north cause you will probably need to add a bit.
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Old 09-14-2015, 01:32 PM   #5
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As stated cold means not driven. However I have noticed that if I check pressures after one side of the coach is in direct sunlight for several hours that side will show higher pressures. Normally I just check tire pressure in the mornings and don't worry about it too much.
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Old 09-14-2015, 03:29 PM   #6
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Cold tire pressure means inside tire temp is outside tire temp, that simple.
But not only driving makes inside tire temp go up, also sunshine on tire and severe braking, but thats only when driving.

Officially cold inside/outside is for 18 degr C/65 degr F , I had contact with a valve importer and he comfirmed this.

When temp in tire is lower or higher the pressure droppes or highenes up, wich gives more or lesser deflection so more or less heatproduction, But because difference between in and outside tire temp is also more or less the cooling down of tire is also more or less .
So if you go from 18 degr C/65 degr F . and recalculate cold pressure for the temperature of the inside so outside tire , tires never get to hot so damage to them.
And thats the main goal of pressure for the load and speed.
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Old 09-14-2015, 05:01 PM   #7
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Direct sun warmth will raise pressure. If you have 78# in the shade, I wouldn't bother adding 2 pounds.
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Old 09-15-2015, 07:46 PM   #8
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Quote:
Officially cold inside/outside is for 18 degr C/65 degr F , I had contact with a valve importer and he comfirmed this.
And that relates to tires how?

Now if that was the Tire Industry Association, or the Rubber Manufacturer's Association, it would have some importance.

Tire Inflation Pressure | TIRE INDUSTRY ASSOCIATION
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Old 09-16-2015, 10:43 AM   #9
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I asume that valves used for cartires use the same standards in temperature for wich pressure is given as car tires pressure.

The guy from the valve importer in Holland ( Europe ) gave me documents in wich 3 standards DIN ( deutche industry norm) , ETRTO ( European tyre & Rimm Technical Organisation) and TRA ( tire & Rimm Assosiation).
And they all go from 18degr C/65degr F.

When filled 80 psi at 65 degr F it will be at 32 degr F ( freesing point of water??) 74 psi and at 100 degr F ( body temperature so hot enaugh I think) 86.3 psi.
So a serious enaugh difference to take into account, is my opinion.
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Old 09-17-2015, 09:35 AM   #10
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I don't think anybody denies that pressure changes with temperature - Robert Boyle (Boyle's Law) proved that. Pressure changes 1.8% (not 1.8 psi) for every 10 degrees (F.) of change.

The question is whether tire engineers specify an ambient temperature at which the "cold" pressure is measured. They do not. If the tire says 80 psi cold, then it should be 80 psi whether the ambient temperature is 30 F. or 100F.
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Old 09-18-2015, 10:29 AM   #11
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Quote:
Originally Posted by jadatis View Post
Cold tire pressure means inside tire temp is outside tire temp, that simple.
But not only driving makes inside tire temp go up, also sunshine on tire and severe braking, but thats only when driving.

Officially cold inside/outside is for 18 degr C/65 degr F , I had contact with a valve importer and he comfirmed this.

When temp in tire is lower or higher the pressure droppes or highenes up, wich gives more or lesser deflection so more or less heatproduction, But because difference between in and outside tire temp is also more or less the cooling down of tire is also more or less .
So if you go from 18 degr C/65 degr F . and recalculate cold pressure for the temperature of the inside so outside tire , tires never get to hot so damage to them.
And thats the main goal of pressure for the load and speed.

Its just a small detail but STP aka Standard Temperature and Pressure is an International standard that is 20degC/68degF at 1030 mb I believe. Since air pressure varies relatively little unless you are in the mountains, this means that the 80 psi reference is based on 68 deg and a 78 deg ambient should require a 1.2 psi increase. So a mid day tire check in mid summer out of direct sunlight where the ambient in TX can easily be 105 should indicate about 85 psi or thereabouts
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Old 09-18-2015, 10:43 AM   #12
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Quote:
Originally Posted by R1Kirby View Post
The manufacturer says 80 pound cold temperature. So the outside temperature is 75 degrees and the tire pressure is 80 pounds. In the morning it is 59 degrees and the tire pressure is 78 pounds. So what cold temperature does the manufacturer have in mind? It does get confusing......
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Old 09-18-2015, 11:57 AM   #13
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Quote:
Originally Posted by Gary RVRoamer View Post
I don't think anybody denies that pressure changes with temperature - Robert Boyle (Boyle's Law) proved that. Pressure changes 1.8% (not 1.8 psi) for every 10 degrees (F.) of change.

The question is whether tire engineers specify an ambient temperature at which the "cold" pressure is measured. They do not. If the tire says 80 psi cold, then it should be 80 psi whether the ambient temperature is 30 F. or 100F.
Gary - Interesting, I'll do some more research on Tireman9's site about this. I've always used the magic 65 degree, and set my desired tire PSI in accordance with that. And, I adjust up or down, based upon the infrared temp reading to he tire, to be at the desired pressure, based upon how much higher or lower the temperature reading is. (Always try to do this on a relatively warm day, and usually in the San Diego area along the coastal zone, I'm within 5 degrees of 65 in the AM when doing my tire pressure settings!

I run with what I feel is an adequate safety cushion of PSI above the tire manufactures PSI charts for our four corner weight. And with that safety margin, I typically do not adjust up/down my PSI based upon traveling location swings in temperatures. I have my TPMS low/high PSI and Temp settings, set to warn me while traveling of any concerns form changes in PSI or Temps.

On other threads about how often to we set our tire PSI's, I mentioned that due to the very little loss of PSI for my tires, that I could go a full year without having to add PSI. (Check them daily via TPMS, and visual inspection. And monthly with my tire gauge. And, about once a week when doing traveling and pulling off the road, I check double check tire temps with the infrared.)

I did make an adjustment to PSI while knowing I was going to be above 8K feet for about 7 weeks, around the Denver and Rocky Mountain National Park area. The reset when leaving Colorado Springs as we headed East into Kansas. But, I probably would have been fine without adjusting for the altitude, due to the safety margin, and still being way below the 120PSI Max Cold Pressure for my tires/rims.

I'm in the camp of doing your research for your tires, and your specific weights, adding that safety margin of PSI - and then going on out and not being too overly concern with the PSI. Again, with the mentioned daily and weekly and monthly checks.

When I'm starting off on a extremely cool day, say between the 20's and 30's, I usually just do a more gradual coming up to speed. For both the engine, and the tires, as they are both coming up to temps. Only one time have I had a TPMS warning, along the Alcan, as we pulled out from an ice covered Muncho Lake with an outside temp of 18 degree.

Until recently, all 8 of my tires were Michelin XZE*. with the "*" meaning a bit extra thickness on the sidewalls. This may be one of the reasons our tires do not seem to loose very much on the PSI front over a years period.

I'll do some more checking on Tireman9's blog, to see if I want to change my processes!

Best to you, and all. And, I do encourage every RV'er to really understand the importance of tire maintenance and PSI's in relation to not only your safety, but those traveling on the roadways along side of you!
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Old 09-19-2015, 03:04 PM   #14
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For those who wish to learn more, read about "Cold Inflation Pressure" on Roger Marble's RVtiresafety.com web site.
RV Tire Safety: Cold Inflation

For those who want the short summary, I'll offer this short quote:

Quote:
I occasionally see posts on the need to do an adjustment of your Cold Inflation Pressure ( CIP )when the temperature is not at some "standard".

Many times the "standard" is stated to be 70F or 68F. Neither of these are correct.

From a tire design standpoint CIP means when a tire has not been warmed up either by being in direct Sunlight or from having been run.
We are not talking about some chemistry lab experiment but real life. This is defined by the Tire & Rim Association, the organization that published the standards book for tire dimensions and recommended Load & Inflation for all kinds of tires, wheels and valves.

Roger Marble
aka Tireman9
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