Tire pressure in cold weather

[btbaillie]

We are getting ready to travel this week from Colorado to Arizona for the winter. The last time I checked the tire pressure, it was warm out and all 4 were at 80lbs. Today it is 24 deg. and the pressure is 70lbs.

Will the pressure drop 10lbs? Should I increase the pressure?

Bruce & Lu

 

[scottyb]

Yes. My TST 507 is set to alarm at 72 PSI. Before I take off on a cool morning (35 -40), I check the tire pressures manually and it is somewhere between 72 - 74. I know it's the cold because they are all the same and I have pretty much established a baseline with them over 10K mi. Occasionally, I have to turn off the TST until they have had time to warm up a little or just silence the alarm. It will resume normal operation once they are all above 72 and they are usually back up to 80+ in a very short time. I think they are supposed to be 80 psi @ 72 degrees or something very close to that.

 

[HornedToad]

Here is a great reply from danemeyer to a similar question I posted...

Hi HornedToad,

80psi is the "cold" pressure where "cold" means the ambient temperature is 70 degrees (F), before you start driving, tires not in direct sun. If temps are lower, on an 80psi tire, you lose about 1.5 psi for each 10 degrees. At 40 degrees, you should be seeing a pressure of around 75psi. If it were 90 degrees you'd see around 83psi. After driving for a few minutes, the pressure climbs, often quite a bit.

On load range G tires, like the Goodyear G614 that we have, the cold pressure is 110psi and the change is closer to 2psi per 10 degrees. If I start at 110psi, after 15 minutes on the road, the pressure might reach 120psi. On a hot summer afternoon, it can go even higher.

 

[Jadatis]

I once made a spreadsheet to play with the pressures and see wat it does to the temperature and the other way around.
Here a picture wich prooves that it can get that low.
Fooled the program a little with filling cold in the place of warm and around.
Best is to fill cold now at 80 psi , then when outside temperature gets warmer cold pressure will rise to about 90 psi , wich is allowed for a 80 psi ST and LT tire by the tire maker.
If you have metal valves , they can also stand the higher pressure.
The 90 psi gives that extra savety for the tires , because ST tires are mostly used to their maximum , and because of shifted weight R/L one tire can get overloaded sooner. But there is a danger if your tires are already damaged by to low pressure, and then you fill them that high, the damaged tire blows.
But if you did not make many miles or for new tires sertainly this higher pressure gives longer lasting tires and extra savety.

 

[GOTTOYS]

I once made a spreadsheet to play with the pressures and see wat it does to the temperature and the other way around.
Here a picture wich prooves that it can get that low.
Fooled the program a little with filling cold in the place of warm and around.
Best is to fill cold now at 80 psi , then when outside temperature gets warmer cold pressure will rise to about 90 psi , wich is allowed for a 80 psi ST and LT tire by the tire maker.
If you have metal valves , they can also stand the higher pressure.
The 90 psi gives that extra savety for the tires , because ST tires are mostly used to their maximum , and because of shifted weight R/L one tire can get overloaded sooner. But there is a danger if your tires are already damaged by to low pressure, and then you fill them that high, the damaged tire blows.
But if you did not make many miles or for new tires sertainly this higher pressure gives longer lasting tires and extra savety.

View attachment 27636

Sorry is it just me or does this chart and all not make much sense?... Let's simplify all this....Check the tires in the morning before you start out. Set them at max pressure, be it 80 PSI or 110 PSI. Park for the night. The next morning before you start out check them again and readjust the pressure. They will gain a little pressure as you drive throughout the day and as the ambient pressure warms up. Mine have gained as much as 10 PSI. In the morning the next day they will usually be back to the 80 PSI they were set at. All good. End of story....Don

 

[scottyb]

Glad someone else saw the same thing. I was having a hard time interpreting the chart as well.

So if you set them at 80 when you leave home where it's 70 degrees, and stop somewhere it gets down to 30 degrees, you add more air the next morning? My tires usually rise 10 - 14 psi when travelling. My thoughts are that if all 6 tires are at the same level the next morning, that's OK. The likelihood that all six of them had a leak and lost the same amount of air is unlikely, and it is just a response to the colder temperatures. If one tire is significantly lower than the others, obviously it requires air to be added. I'm afraid that if I set the pressure at 80 when it's 30 degrees outside, they will exceed the high limit on my TST 507.

 

[DW_Gray]

Excellent question and some excellent responses. Here are some more links to my favorite tire expert, Roger Marble (tireman9):

http://www.rvtiresafety.net/2012/09/tire-pressure-increase.html

http://www.rvtiresafety.net/2012/09/adjust-tire-pressure-for-better-ride.html

http://www.rvtiresafety.net/2011/05/tire-temperature-pressure-hot-topic.html

 

[PUG]

we are getting ready to travel this week from colorado to arizona for the winter. The last time i checked the tire pressure, it was warm out and all 4 were at 80lbs. Today it is 24 deg. And the pressure is 70lbs.

Will the pressure drop 10lbs? Should i increase the pressure?

Bruce & lu

attached please find air pressure chart for different size tires, air pressure base pressure and air pressures per temperature outside. Hope this helps

 

[Jadatis]

Sorry is it just me or does this chart and all not make much sense?... Let's simplify all this....Check the tires in the morning before you start out. Set them at max pressure, be it 80 PSI or 110 PSI. Park for the night. The next morning before you start out check them again and readjust the pressure. They will gain a little pressure as you drive throughout the day and as the ambient pressure warms up. Mine have gained as much as 10 PSI. In the morning the next day they will usually be back to the 80 PSI they were set at. All good. End of story....Don

What my picture shows is that if you have fillled at 80 degr F a pressure of 80 psi , then at 24 dgr F it will be that 70.2 so the 70 that topicstarter measured.
So the pressure lowering is only courced by the temperature lowering, so no leaking in that period.
So if the temperature gets that 80 degr again the pressure will rise back to the 80 psi.
But its better to get a cold pressure when ambient temperature is 24 , of 80 psi to give the tires a deflection that is save for them.
But I already wrote that I messed around a bit with the place to fill in , so the picture can be somewhat confusing.
The calculations thoug are acurate ,asuming the pressure and temperatures are 100% exact given , wich is never possible.
Also the spreadsheet asumes no vollume chanching of the tire when the pressure chaches in it, wich it will be about for a already presurised tire.

Tougt I did help the topicstarter to make things clear, but does not seem to be apreciated.

 

[TXTiger]

Remember this is just a guide. Your tire pressure does not have to be EXACTLY 80 psi or 110 psi. It can vary by a few psi without any harm to the tire. As long as you are in a range of say 72 to 90 you will be ok. Your tire pressure will rise as you drive and the tire heats up and go back down overnight while you are parked.

 

[jimtoo]

You are so right Tony. How about when you hit a chughole in our great highways... pressure will go from 80 to what??100,,,110# for an instant? I have watched the airbag gauge I have on my truck,, normal for me hooked up is 30#,,, but when I hit a big dip or hole I have seen the gauge hit 50-60#. So if my tires have 75-80# at 70-90° I am good to go.

 

[scottyb]

What my picture shows is that if you have fillled at 80 degr F a pressure of 80 psi , then at 24 dgr F it will be that 70.2 so the 70 that topicstarter measured.
So the pressure lowering is only courced by the temperature lowering, so no leaking in that period.
So if the temperature gets that 80 degr again the pressure will rise back to the 80 psi.
But its better to get a cold pressure when ambient temperature is 24 , of 80 psi to give the tires a deflection that is save for them.
But I already wrote that I messed around a bit with the place to fill in , so the picture can be somewhat confusing.
The calculations thoug are acurate ,asuming the pressure and temperatures are 100% exact given , wich is never possible.
Also the spreadsheet asumes no vollume chanching of the tire when the pressure chaches in it, wich it will be about for a already presurised tire.

Tougt I did help the topicstarter to make things clear, but does not seem to be apreciated.

Sorry Jadatis, didn't mean to sound unappreciative. Just didn't understand your chart. It makes perfect sense after you spelled it out for us. It also agrees with what I have seen with my tires as well.

 

[DesertThumper]

Remember this is just a guide. Your tire pressure does not have to be EXACTLY 80 psi or 110 psi. It can vary by a few psi without any harm to the tire. As long as you are in a range of say 72 to 90 you will be ok. Your tire pressure will rise as you drive and the tire heats up and go back down overnight while you are parked.

All good stuff here. I agree with Two Toes and others. I wanted to add my two cent experience with pressure monitoring for comparison purposes or for others that may not know about tire pressure safety.

The temp is a big player when filling up your tires before leaving. I would fill up my six trailer tires between 70 to 75 PSI at cold with an outside estimated temp of 50 - 65 degrees. Once on the road, the current temp outside will increase 10 + degrees. This is with the current temps now. Our last trip, we set them to 75 PSI cold @ 60 degrees outside. After two hours of driving, truck and trailer tires were re-checked for air pressure = 83 PSI. a previous trip before this one, when the weather was much warmer (83 degrees), I had to set them at 70 PSI (65 degrees outside - cold PSI). After two hours, checked all the tires and they = 80PSI on the nose. Heat will rise once on the highway and bring the current PSI settings to a greater number. Of course, this will factor in your current condition and place. The specs above is my own experience with tire pressure maintenance - here in CA.

Where did I learn this method: I ask for second opinion from the tire guys locally just to make sure I am not shooting from the hip when dealing with tire pressure guidelines.

I have been doing this drill for some time now including previous trailers we've owned and knock on wood, no tire blow outs. It seems most of us got a good understanding of pressure and tire maintenance. These are important factors when your towing a heavy pig behind you.

The more we put out on the portal, the better we can better educate each other for highway safety. It's kind of align and re-align your knowledge base to make you a smarter and responsible driver. There's always great information being shared here - Thanks.

 

[Jadatis]

Sorry Jadatis, didn't mean to sound unappreciative. Just didn't understand your chart. It makes perfect sense after you spelled it out for us. It also agrees with what I have seen with my tires as well.

To make things clearer , I made a new picture , in wich cold is cold pressure ( so inside and outside the tire the same temperature), and warm is warm, so the smaller written dark green fields.

But about the needed pressure , TwoToes writes that is does not have to be exact, and it even may vary between 72 and 90 for a 80 psi tire.
I dont agree with that , if he means cold pressure . 5th wheelers as topicstarter has ( openened the picture) often have ST( special trailer) tires wich are calculated in their maximum load for maximum speed of 65m/h.
I once compared an ST and LT tire of almost the same sises and concluded that the ST had 15% more maximum load then LT. So STmaxload=1.15 * LTmaxload. This is mainly because for lower speed the tire is more deflection allowed wich gives larger surface on the ground so more load to carry at the same pressure.
Now 5th wheelers and other trailers mostly have tires that can bare yust enaugh to cover the GAWR ( gross axle weight rating) .
Thats the reason why tires for trailers in general need to be pumped up to their maximum, and then still the deflection is to its maximum that is allowed to give no tire-damage at the speed its meanth for.

If now the cold pressure drops because of the temperature drops, as here is the case, the tires get to much deflection.
So its best to pump the tires to even 10 psi more then that 80 psi here, so 90 psi cold.
Then at 80 degrF it has some reserve, and the tire deflects less , probably the same a LT tire would do, wich is saver for the tires.
If then the temperature drops , the cold pressure drops to a level that is still save for the tire, so the deflection does not go over the border where damage is done to the tire. In an European list of semperit(continental) even a 40% higher cold pressure then needed for the maximum load ( that 80 psi here) is allowed to give the tire a loadcapacity of 2 times the given maximum load, when standing still so speed zero, so you dont have to be afraid if the pressure cold gets more then 90 psi when the outside temperature is hotter then 80 dgr.
For a 80 psi tire 90 psi is only 12.5% higher so there is still some reserve to laws of nature.
For a 50 psi maxloadpressure tire this 10 psi is also alowed extra and then even 20% above maxloadpressure wich is half way down what the semperit document gives as maximum cold pressure .
Warm it will be even higher , when standing still only the outside temperature can rise the pressure , so I asume the absolute highest pressure the tire-maker stands in for , is about 1,5 times the maxloadpressure ( that 80 psi here).
So filled to 90 psi at 65 degrees it can rise to a warm pressure ( so inside tire warmer then outside tire) of mayby 110 psi wich is 37.5% higher then 80 psi so still within the savety margin of 50%.


And that 90 psi is allowed for ST and LT tires by the tire-makers organisation TRA.

I also made a multilingual tire-pressure calculator for Travel-trailers one for motorhomes.
The TT calculator is most simple to use , and also gives tonge-weight percentage of total.
The motorhome calculator can also be used for this, and gives more variations to play with it and set it to your own ideas, but needs some inventivaty of you.
The Traveltrailer- map here
https://skydrive.live.com/?cid=a526e0eee092e6dc#cid=A526E0EEE092E6DC&id=A526E0EEE092E6DC!348
And the Motorhome-map here
https://skydrive.live.com/?cid=a526e0eee092e6dc#cid=A526E0EEE092E6DC&id=A526E0EEE092E6DC!793

To download a spreadsheet , CLICK RIGHT and choose DOWNLOAD.
Dont use leftclick or when rightclicked "open in Excell "or 'Open in WEB-APP, askes you to login with your hotmail adress or cant handle things I used in most spreadsheets and gives error message.
Thats the disadvantage of the Skydrive , that belongs to my hotmail adress with same username as in this forum, wich I use to store my spreadsheets and pictures ( also this above picture is stored there).
It is meant to use together with Office ( word ,Excell etc) to store your files in the cloud.
But if you leftclick it is openened in an excell like programm in the cloud, wich cant handle some often used things like data validation and sheet-protection.
If you leftclick an xls file ( for older excel usable) is chanched to a xlsx file ( for Excell 2007 and newer) and even a bit damaged so for instance you cant chanche the language anymore. So then you spoil it for the others , but I dont blame you , I do it myself by accident too myself.Then if this happens you can get the old xls file downloaded by using version-history so its not lost.

So my advice is to calculate the needed pressure, and use for ST tires only 80% of the given maximum load.
This gives the ST tire the same deflection a LT tire would get when used for dual load, wich is also saver for tandem-axle ( or tripple), because of the large sideward forces when curving, and the unequall loading R/L and between the axles ( so one tire can have much more load on it then the others). Once saw in another forum a difference of 800 lbs between the highest and lowest load on a tamdemaxle 5th wheeler with even crossed weight-differences R/L between the axles.
Then if the adviced pressure with even up to 10% reserve comes to 90 psi for a 80psi tire it is ok.