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Old 01-21-2014, 12:13 AM   #1
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Tire pressure in varying temps

I am not sure how to handle tho safely. We have traveled in the past in climates where the temps don't vary too much. But this year it's been interesting. We spent about a month near Miami and had constant temps for the most part. Tires were right at 65psi when cold and off we went to continue our trip west to CA. We are now seeing temp in the 30s at night and anywhere from 50-75 during the day. I am not sure how to handle tire pressure. For example when we left this morning the tires were at 59-61 psi but it was 37 and was going to get into the upper 60s and we had an 8 hour drive planned. When we pulled in to destination tires were at 63-64psi. I am not sure if I should be setting tires to 65 even if it there is a big difference in temperature. I don't want to over or under inflate and want to say safe out there. Thank you so much for any guidance!
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Old 01-21-2014, 12:29 AM   #2
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Hi, I set my tire pressures at home just before each trip; I never check them or make any changes during my trips. Where I live now, the temperatures are almost always moderate. In one trip, we hit temps as low as zero and as high as 100 degrees. On my Alaska trip, we were gone for 50 days and for over 10,000 miles; My tire pressures were only changed because of two tires that started to separate. Therefore, new tires, new air.
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Old 01-21-2014, 04:55 AM   #3
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Originally Posted by Thomas_G View Post
I am not sure how to handle tho safely. We have traveled in the past in climates where the temps don't vary too much. But this year it's been interesting. We spent about a month near Miami and had constant temps for the most part. Tires were right at 65psi when cold and off we went to continue our trip west to CA. We are now seeing temp in the 30s at night and anywhere from 50-75 during the day. I am not sure how to handle tire pressure. For example when we left this morning the tires were at 59-61 psi but it was 37 and was going to get into the upper 60s and we had an 8 hour drive planned. When we pulled in to destination tires were at 63-64psi. I am not sure if I should be setting tires to 65 even if it there is a big difference in temperature. I don't want to over or under inflate and want to say safe out there. Thank you so much for any guidance!
Check tire pressure at the beginning of the day, when the tires are "cold" from not moving overnight. If you drive into colder or warmer temps, don't sweat it, because while you're underway, the tires are no longer "cold" due to sidewall flex and other movement.
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Old 01-21-2014, 06:30 AM   #4
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Another way to approach this problem is to figure out what the lowest temperature you will encounter, pressurize your tires for that and not worry until you get to where the temperatures are consistently higher than your starting point.

Example: Let's say you are at 60°F now and the lowest temperature you will encounter is 30°F, and you want 65 psi. In that case you'll need to put in 70 psi.

I think I need to explain where I got that from. I'm using the Ideal Gas Law - and I have programmed that into my computer. The rule of thumb for passenger car tires was 1 psi for every 10°F, but because the pressure is higher, that doesn't work. Looking at this it looks like it is double that for the higher pressures in ST and LT tires.

Now, some will point out that the pressure is higher than the maximum listed on the sidewall of the tire - and I will tell them to look again, because it doesn't say maximum. It says "maximum load AT 65 psi" (or whatever) - a relationship. It doesn't say what the maximum pressure is - AND - These types of tires can use more pressure than is listed by the relationship - just don't try to overdo it, certainly not more than 10 psi (cold).
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Old 01-21-2014, 09:42 AM   #5
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An easy way to fix your problem would be to use Nitrogen which is less affected by heat/cold temps. In fact, most shops already use it in cars/trucks. It will cost you a few bucks more to have them put it in your trailer tires. But remember, even standard air is made up of about 78% Nitrogen and 21% oxygen.

In case you want more info, take a look at the link below.

Nitrogen vs Air In Tires - Why Nitrogen in Tires - Popular Mechanics



Enjoy,
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Old 01-21-2014, 10:46 AM   #6
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Check tire pressure at the beginning of the day, when the tires are "cold" from not moving overnight. If you drive into colder or warmer temps, don't sweat it, because while you're underway, the tires are no longer "cold" due to sidewall flex and other movement.
First of all, I have a degree in Atmospheric Sciences, So I have some understanding of how gases behave.

In my opinion the above quote is the most sensible post so far. Tire inflation pressures do not require the application of rocket science.

If you are going to worry about the changes in air temperature that can occur with one day's travel, you'd best also start thinking of the changes in atmospheric pressure that can occur as you go over mountains and down into valleys and travel from good weather into lousy weather.

If all of this seems a big nuisance, do what I do and use a TPMS (tire pressure monitoring system). It will save the time spent checking everything manually and will give great peace of mind while driving. It may even return some of your investment, by catching a slow leak before it turns into a catastrophic failure.

Also remember for any given situation, there is not one absolute ideal tire pressure. Think of it instead as a range of acceptable pressures.

If you want to read experimental data about the value of nitrogen in tires, read this:

http://powertank.com/truth.or.hype/

Ken

P.S.

Another factor that does not get mentioned often in these tire pressure discussions is the accuracy of the gauges used to measure tire pressures. Unless you pay more than most of us do, the accuracy is often poor.
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Old 01-21-2014, 11:12 AM   #7
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We travel into and from varying temps. Our solution:

1) Buy a TPMS ( tire pressure monitoring system) e.g. TST ( Truck System Technologies) to measure and "keep track" of temps and psi.
2) Take all of 10 seconds to check your tire "vitals" in the A.M. when the tires are cold. Rarely do you have to "top off" on air. Repeatedly checking the tires can possibly wear out the valve stems…..I once had THREE fail on the same day of departure. Absolutely ruined my day!
3) Keep an eye on the temps and the psi while traveling. If the tire temps approach 110 degrees…pull off and cool down. ( the max is about 125 degrees--- if they overheat, there is irreparable damage to the tire itself)
4) Occasionally, when traveling to higher altitudes and lower temps….e.g. Yellowstone, Glacier, etc, I'll have to add more air--psi.
5) I have been advised by multiple tire shops to carry the max psi on the tires at all times. Tires fail with overheating particularly if under inflated ( >10% or more under inflated) or over loaded. We carry "E" rated tires ( Michelins) I keep my margin of safety much narrower! ( 5%…no less than 76psi on an 80 psi tire)

Opinions will vary, but that's my story and I'm stick'n to it!
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Old 01-21-2014, 11:37 AM   #8
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It is interesting to read the comments on this topic. I struggle to understand the answers here and elsewhere. If I bring my trailer tires up to the max 65 psi when it is cold outside and before using them, I will have to let air out when it gets to a warmer season to keep the cold starting pressure at 65 psi. For my car (kept in a semi heated garage) but driven in the same temperature as the trailer I will have (relatively speaking) higher pressure since I am measuring the car psi in a warmer place. Why does this make sense?
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Old 01-21-2014, 11:56 AM   #9
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It is interesting to read the comments on this topic. I struggle to understand the answers here and elsewhere. If I bring my trailer tires up to the max 65 psi when it is cold outside and before using them, I will have to let air out when it gets to a warmer season to keep the cold starting pressure at 65 psi. For my car (kept in a semi heated garage) but driven in the same temperature as the trailer I will have (relatively speaking) higher pressure since I am measuring the car psi in a warmer place. Why does this make sense?
In theory that is true. In reality, you will probably have messed with the pressures many times during the seasons. If the tire has been standing unattended for a significant period it will have lost air anyway.

Why does this make sense?

Because it is not necessary to be exact. There are so many variables that change minute to minute and day to day that it would be impossible to keep up with them. So it is futile to attempt to make this whole process exacting. Get your pressures in the ball park and check them periodically.

If you are not comfortable establishing the acceptable range, talk to your tire dealer, or even better, customer support at the tire manufacturer.

Ken
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Old 01-21-2014, 12:08 PM   #10
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It is interesting to see how much attention is given to trailer tires. Also how many are run a max pressure. Some are run at pressures that are higher than the rated rim pressure.
When one checks the tire pressure on the TV, the pressure is set at the placard (door frame) specs. Most placards show a different pressure for the front verses the rear tires. Based on the axle load.
But in no case are the TV tires inflated to the max pressure.
Why then, does one think the trailer tires must be run at the max rated pressure?
The total load carrying capacity of the 4 tires on my coach is over 10,000# at max pressure. My coach weighs 5,500# loaded for travel.
I run 55# in each tire, which are ST's. have towed some 20K miles with no problems.
I expect the tire pressure cold to be different than hot. I also expect that the pressure would be less at +10 when compared to +70 and even higher at temps above +100.
I also expect the pressure to change with changes in altitude.
I have traveled 9,000 miles this year over a 6 week period and have not found it necessary to add or remove air.
If it ain't broke. Don't fix it.
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Old 01-21-2014, 12:28 PM   #11
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Originally Posted by TG Twinkie View Post
It is interesting to see how much attention is given to trailer tires. Also how many are run a max pressure. Some are run at pressures that are higher than the rated rim pressure.
When one checks the tire pressure on the TV, the pressure is set at the placard (door frame) specs. Most placards show a different pressure for the front verses the rear tires. Based on the axle load.
But in no case are the TV tires inflated to the max pressure.
Why then, does one think the trailer tires must be run at the max rated pressure?
The total load carrying capacity of the 4 tires on my coach is over 10,000# at max pressure. My coach weighs 5,500# loaded for travel.
I run 55# in each tire, which are ST's. have towed some 20K miles with no problems.
I expect the tire pressure cold to be different than hot. I also expect that the pressure would be less at +10 when compared to +70 and even higher at temps above +100.
I also expect the pressure to change with changes in altitude.
I have traveled 9,000 miles this year over a 6 week period and have not found it necessary to add or remove air.
If it ain't broke. Don't fix it.
I will answer for this one of the ones. I do not believe that the tire must be run at the sidewall stated pressure. I do it because I know that the sidewall pressure is safe at all loads and conditions for which the tire is rated. I would rather risk premature tire wear in the center of the tread, than mess around with figuring what the actual weight on each wheel is for every trip. Since my trailer is fairly heavy, the suggested pressure for the load would be fairly close to sidewall pressure. To address all the variables you mention: One must start somewhere.

Ken
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Old 01-21-2014, 01:09 PM   #12
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Couldn't help but post a few comments on this one:

1. Nitrogen behaves just like good ole everyday air within the predictions of the ideal gas law. It is not magic. Thanks Ken (Ag&AU) for posting your link.
2. I seriously doubt one can find a tire shop that will take the time to inflate tires to the appropriate and consistent pressure much less give you a true nitrogen fill. They are highly unlikely to fill and purge the tire to the extent necessary to achieve anything near a true nitrogen fill. I'd suggest you give your nitrogen fill money to a good charity and get someone in need something for it.
3. Who has a N2 bottle with them to inflate the tire when it is needed?
4. Read Capri's post here and elsewhere very carefully, he knows what he is talking about. He has been an excellent source of reliable information on this forum and others on the topic of tires, pressures, failures, etc. Thanks Capri for your continued efforts to help folks on these topics.
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Old 01-21-2014, 03:01 PM   #13
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Well, these responses have been absolutely amazing. Thank you all.

From reading all these posts and links within, I think I will just set the pressure in the morning tomorrow near 65psi just to establish a starting point again as the temps are now considerably lower than in south Florida. I will also be less stressed about having them exactly at 65psi (Max) as it seems that is not always the "best case".

Thank you again!!
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Old 01-21-2014, 05:17 PM   #14
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Fill tires to specified pressure before the vehicle moves. If you are going to check the pressures at all after traveling, the pressure data is meaningful only in comparing differences in pressures amoung all of the tires on one vehicle. If there is a spread there are issues! The actual tire pressure after the tire has been on the road is meaningless.

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