Tire pressure and temperature

[HRDWRK]

We know as the outside temperature drops, the cold tire pressure will drop. Also, as the tire rotates, the tire temperature increase and so does the tire pressure. Now my questions is: I set my cold tire pressure (class C Ford chassis) in SoCal at 75 PSI up front and 80 PSI on the rear based on factory recommendation.  The temperature was about 75 degree at the time. While in motion my tire pressures usually increase by 7-10 (or more) based on the tire temperature and I guess the outside temp. I have one of the TST tire pressure system which shows tire pressure and temperature. When we were in Reno/NV, the outside temperature dropped to low 40s and my cold tire pressures dropped by 5-7 PSI at different locations which made m TST unit unhappy. Since after 10-20 minutes of driving and when the tire temperature reaches 60ish or so degree the tire temperature reaches the recommended setting, is it advised to adjust the cold tire temperature when temperature drops like this?
Thanks

 

[Larry N.]

I'd suggest you make the adjustment if the cold will last long, since the tire mfr sets the recommended pressure for cold inflation and checking, with built in allowances for the temperature and pressure changes that come from rolling down the road. But I'd probably not change it if I expected the weather to be warmer for me (and stay that way) a couple of hours later (perhaps going in the mountains then coming back down).

 

[Henry J Fate]

It wasn't to many years ago that tire pressure monitors were not around very much and it wasn't easy to detect changes in tire pressure. Tires are designed to handle the changes in pressure. The fluctuation is more about the tires wearing evenly under a given load than safety however safety is a factor. As Larry mentioned, if you are going to be in a sustained temperature, set your tire pressures for that temperature. People who live in the north will find large swings in the average temperature and tire pressures should be adjusted accordingly. In addition to tire pressure, the other indicator of tire maintenance is visual inspections to see how the tires are wearing. Tires that show more outer edge wear would generally indicate low pressure conditions. Tires that show more tire wear in the middle would generally be too high in pressure. Front tires have a tendency show accelerated wear from other factors but in general, the same rule applies and front tires should be rotated to the rear on reasonable intervals based on usage. The visual inspection is quite helpful as it allows for small adjustments to pressure for better tire wear and will indicate when rotation is needed. Its important both in the pocketbook and the quality of the life of the tires to visually inspect on a regular basis and make the appropriate adjustments.

 

[Gary RV_Wizard]

is it advised to adjust the cold tire temperature when temperature drops like this?

The short answer is YES.  The "cold pressure" means exactly that - the psi it should be when the tire is cold.  The cold pressure recommendation already assumes that the tire will warm up and the air will expand - that has been factored into the cold pressure recommendation. Don't try to outsmart the engineers.

Now, is it a big deal if you happen to get hit with an unusually cool overnight and don't bother to adjust, cause you know the next day will be warm again anyway. No, not really.  Assuming the differential is only a few percent (not psi) of the recommended psi, the tire should withstand a short period of such abuse.  If you expect this to be a regular occurrence, make your normal inflation a few psi higher than the recommended minimum.  That way when you encounter a cold snap, you are still close to the recommendation.

 

[jymbee]

...  make your normal inflation a few psi higher than the recommended minimum.

A related question if I may...

I had a low tire pressure warning last week for one of the tires on my TOAD. I brought the pressure back up using our VIAIR portable pump with its digital display. Figured I might as well check all the other tires while I was at it. Recommended pressure is 33 and every one of them, according to the VIAIR, was near 40. Double checked again with the pressure gauge I usually use and that read right around 33. Pretty big difference! Question is how accurate are tire gauges in general?? Just not sure which one to trust...

 

[stvaughn]

A related question if I may...

I had a low tire pressure warning last week for one of the tires on my TOAD. I brought the pressure back up using our VIAIR portable pump with its digital display. Figured I might as well check all the other tires while I was at it. Recommended pressure is 33 and every one of them, according to the VIAIR, was near 40. Double checked again with the pressure gauge I usually use and that read right around 33. Pretty big difference! Question is how accurate are tire gauges in general?? Just not sure which one to trust...

Are you using Viair as per the instructions? It will make a difference in your readings. I do trust my Viair and have confirmed it is accurate with my second gauge.

 

[Gary RV_Wizard]

A decent air gauge is within plus/minus 3% of what a lab-grade instrument would show, but many are as much as 5%, especially after knocking around in a car or tool box for awhile.  Plus you can get sloppy readings if the chuck isn't placed on firmly & cleanly.

 

[jymbee]

A decent air gauge is within plus/minus 3% of what a lab-grade instrument would show, but many are as much as 5%, especially after knocking around in a car or tool box for awhile.  Plus you can get sloppy readings if the chuck isn't placed on firmly & cleanly.

Good points. I'm inclined to trust the readings from the Viair. I have some tire work scheduled next week at my local tire dealer and I'll take it with me and do some tests there.

 

[Patnsuzanne]

For the sake of consistency I use the same tire pressure gauge to check each of our vehicles, as well as our TT. Before each trip I check and adjust the pressure in the trailer tires and then check them against the TPMS. So far there hasn?t been more than a pound or two difference, so that?s encouraging. 

 

[HRDWRK]

Based on what I know, please correct me if I am wrong, most tire blow up happens because of low tire pressure (besides road hazard like puncture etc). So what is low? PSI or percentage wise.
When we were at Reno, the over night temp dropped to 29 degree. The cold temperature  of my front tire dropped from 74 PSI to 69 PSI. When I got on the road, after about 10 minutes, when the tire temperature reached 40 degree, the pressure has climbed to 74 PSI. So what I am trying to understand is it seems at 40 degree ambient temperature the pressure would be still within acceptable range. It seems just a mind game and playing with numbers.
What is the harm or risk of too high of temperature? Besides, tire wear and tear in long run.

 

[grashley]

A related question if I may...

I had a low tire pressure warning last week for one of the tires on my TOAD. I brought the pressure back up using our VIAIR portable pump with its digital display. Figured I might as well check all the other tires while I was at it. Recommended pressure is 33 and every one of them, according to the VIAIR, was near 40. Double checked again with the pressure gauge I usually use and that read right around 33. Pretty big difference! Question is how accurate are tire gauges in general?? Just not sure which one to trust...

Old Chinese Proverb:  Man with two watches never knows what time it is

Check a gauge against 2 or 3 others, and go with the consensus.

 

[Lou Schneider]

Escapees Smart Weigh has a tire pressure gauge tester they bring to Escapades, etc.  It's a small compressor with a tire valve stem and a calibrated pressure gauge.  You set the compressor to your recommended tire pressure, then put your gauge on the tire stem and see how it compares to the calibrated gauge.

The gauges they have tested have either been within a pound or two of the calibrated gauge or grossly off.  There doesn't seem to be anything in between.

 

[xrated]

There are tire gauges out there that are incredibly accurate, if you care to spend the money.  I bought a 0-60 psi gauge for using on my racing motorcycle several years ago, where a 1/2 lb of pressure made a very big difference in tire wear and more importantly...grip!  This gauge is tested and certified to be within 1/2 of 1%.  My normal inflation on the rear tire was 18 psi for best results.  So in that tire, it was +/-  .09 psi.  That is accuracy....if you need it.

 

[FL-Joe]

I have used a TST TPMS since around 2011.  With our current rig I set all my tires after weighing.  It was probably around 70 degrees at the time and during the morning when everything was shaded. 

Our extremes so far this year has been anywhere from 100+ to upcoming lows of 28.  My 22.5 tires will indicate a difference of at least 10psi to 12psi prior to getting on the road.  I never add or remove air. 

 

[Gary RV_Wizard]

So what is low? PSI or percentage wise.

"Low" is less than the psi shown in the inflation tables for the load (weight). The table gives the minimum inflation adequate to carry the load without damage due to internal stress.  The psi is measured when the tire is "cold", which means not driven for at least a few hours. "Cold" is not some arbitrary ambient temperature.
It's not a mind game but the pressure readings change with temperature. For every 10 degrees (F), plus or minus, the pressure inside the tire changes 1.8% up or down (we usually call it 2%, to make the arithmetic easier).  That's 1.8% of the existing pressure in the tire, so if you had measured it at 60 psi when it was 70 degrees, you can expect that it will read  55-56 psi at 30 degrees (a drop of 4 x 1.8% x 60 psi).


If you are confident the ambient will rise substantially before you actually begin driving, you can wait for the rise an check/set the psi then,  or you can estimate what the temperature will be and thus guestimate how much the psi inside the tire will change.  However you do it, don't start driving on the tires until the minimum value in the tables has been reached. In other words, do not assume it will be ok because the tire heats itself up due to rolling friction.  All measurements and evaluations are based on "cold" pressures only.

How low is worrisome?  Any amount of "low" is cause for concern, but most tire experts will admit that 1-5% low for relatively short periods is unlikely to be damaging. They also agree that 20% low will quickly result in internal structural damage and that the tire should be replaced if it ever gets driven when that low.  20% low is considered "flat".  The range in-between, 6%-19%, is No-Man's Land, a place you don't want to go but not necessarily fatal, at least not immediately.

 

[Bill N]

Another tire pressure question if I may.  Due to tornado damage and repairs on our sticks and brick we have not hit the road this year at all.  The unit is still winterized from last winter but I do take it out on the road for about a 25 mile drive and run the generator/heater/air conditioner at that time.  This is done every 3-4 weeks. Ever since I have had the tires changed about 1.5 years ago, my right outside dual has been losing air at a very slow rate - about 5 psi per month.  I suspect it could be connections or the valve core but soap checking those I can reach has not shown any leaks.  So I air it up each time I exercise the coach.  BUT, on my last trip out when the weather has just started to turn cold (40s)the suspect tire was the only one that did not show a reduction in pressure.  After the driving, all the others came up to normal and the suspect tire stayed about the same (85psi).

I have never seen this happen before unless the leak was repaired somehow.  Any ideas.  I still plan to get it checked when we take to the road next season but with age and medical conditions I think my road days may be numbered.  Good thread and thanks for the info.