Tire pressure measuring and inflating.

[Schultz]

I have a Class A, Winnebago Journey. I have an issue/question regarding inflating tires to proper PSI. I know that we are to measure the PSI when the tires are cold (not driven on for a while). I know that the appropriate tire PSI is calculated from the tire pressure charts in combination with the weight on each tire/wheel. My issue is, if my PSI is low then I have to drive from my garage or campground to the service center to have air added and by that time I get to the service center the tire has built up pressure to be over the appropriate COLD pressure. So, do I add or not?
An exapmpe:
Appropriate PSI for the tire/wheel is 105 (when cold)
I measure the pressure before driving and it is 100, so I am 5 lbs low.
I drive to get air and the pressure has built up to 110.
The tires are rated for a max of 110 PSI.
Once at the service center do I add 5 lbs to the 110 up to 115 and go over the max PSI rating of 110 for the tire?

I could not find on this forum the answer to this specific issue. I may be on the forum, but I could not find it.

Thanks in advance for any advise,
Bob

 

[Skookum]

Bob, if you’re willing and able, I’d buy a compressor you can keep with the rig so you can set/check the PSI when cold.

To answer your question, the 110psi max rating is for when the tires are cold. It is expected that the tire pressure will increase with temperature.

If you check your tires cold, and they are 5 pound lower than where they should be, you can safely add 5lbs when the tires are warm. Re-check again when the tires are cold

 

[jackiemac]

If you do buy a compressor make sure its powerful enough for the higher psi ratings.

 

[Onyrlef]

I have a Class A, Winnebago Journey. I have an issue/question regarding inflating tires to proper PSI. I know that we are to measure the PSI when the tires are cold (not driven on for a while). I know that the appropriate tire PSI is calculated from the tire pressure charts in combination with the weight on each tire/wheel. My issue is, if my PSI is low then I have to drive from my garage or campground to the service center to have air added and by that time I get to the service center the tire has built up pressure to be over the appropriate COLD pressure. So, do I add or not?
An exapmpe:
Appropriate PSI for the tire/wheel is 105 (when cold)
I measure the pressure before driving and it is 100, so I am 5 lbs low.
I drive to get air and the pressure has built up to 110.
The tires are rated for a max of 110 PSI.
Once at the service center do I add 5 lbs to the 110 up to 115 and go over the max PSI rating of 110 for the tire?

I could not find on this forum the answer to this specific issue. I may be on the forum, but I could not find it.

Thanks in advance for any advise,
Bob

Short answer is "no". 5 lbs isn't going to make any difference anyway. Meantime get yourself a reliable portable compressor but resist the temptation to micromanage the psi, if you're adding air each morning you've got valve or tire issues. Furthermore, you may find that according to the table for your tires and your Cat Scale weights you don't need to run nearly as high a psi as you may otherwise think. The data plate psi is based on gvwr, not gvw.

 

[Tulecreeper]

Short answer is "no". 5 lbs isn't going to make any difference anyway. Meantime get yourself a reliable portable compressor but resist the temptation to micromanage the psi, if you're adding air each morning you've got valve or tire issues. Furthermore, you may find that according to the table for your tires and your Cat Scale weights you don't need to run nearly as high a psi as you may otherwise think. The data plate psi is based on gvwr, not gvw.

Not always, as I found out when I bought my new truck. Both my pillar and my manual say to keep my tires at 75 and 80 PSI, front and back, respectively - all the way up to and including GAWR. And my max sidewall pressure is 80 PSI. To quote the manual under the Vehicle Loading section:

INFLATION PRESSURE
This is the cold tire inflation pressure for your vehicle
for all loading conditions up to full GAWR.

In every vehicle I've ever owned, including my last two trucks, the every day driving PSI was never more than about 60% of the max sidewall pressure. Even though everything I know tells me to drop the pressure to about 40 PSI, I can't lower the pressure more than 20% below what it calls for (which would be 60 front and 64 rear) or my TPMS will go off and the only way to reset it is to bring them back up to max PSI and start over.

 

[Onyrlef]

"may" is an auxiliary verb denoting "possibilty". In a MH the possibilty is very high.

 

[Skookum]

I disagree, 5 lbs is 5% at 100psi. Accurate and even pressure is important.

You want to make sure duals are even, pairs, and either end of the axle.

 

[Onyrlef]

I disagree, 5 lbs is 5% at 100psi. Accurate and even pressure is important.

You want to make sure duals are even, pairs, and either end of the axle.

So what should he do when he's driven 200 miles,the ambient temp is 100°, the tires are @ 120° and the psi has risen to 110, let pressure out?

 

[Domo]

I'd bet one of your neighbor campers has a compressor if you cared to ask... if not at this campground, then at the next. Heck, I've often loaned mine with hose and gauge to fellow campers.

That way you can avoid all the squawking about the subject.

Of course, I only inflate mine when the moon is full...

So what should he do when he's driven 200 miles,the ambient temp is 100°, the tires are @ 120° and the psi has risen to 110, let pressure out?

and... BTW - you never release pressure from a hot tire as you won't know what it will be when they are cold.

 

[Tulecreeper]

I disagree, 5 lbs is 5% at 100psi. Accurate and even pressure is important.

You want to make sure duals are even, pairs, and either end of the axle.

So what should he do when he's driven 200 miles,the ambient temp is 100°, the tires are @ 120° and the psi has risen to 110, let pressure out?

As much as it pains me I'll have to agree with @Onyrlef here. I.E., if my front is off by 5%, that is only ~4 PSI. Not enough to make me want to pull over and do something about it immediately. I wouldn't run them like that forever, but for up to a day or two won't harm anything.

 

[Onyrlef]

That way you can avoid all the squawking about the subject.

Which of course is not what you’re doing. Otherwise, you never add or subtract pressure from tires unless they’re cold, which is a close as you will come to a fixed reference point.

 

[Domo]

Which of course is not what you’re doing. Otherwise, you never add or subtract pressure from tires unless they’re cold, which is a close as you will come to a fixed reference point.

And, I have never said otherwise.

 

[Skookum]

So what should he do when he's driven 200 miles,the ambient temp is 100°, the tires are @ 120° and the psi has risen to 110, let pressure out?

Probably not. Theres a temperature-pressure chart for that, and the mileage driven is irrelevant. Otherwise, check/fill when cold, it’s easier.

 

[CharlesinGA]

Not always, as I found out when I bought my new truck. Both my pillar and my manual say to keep my tires at 75 and 80 PSI, front and back, respectively - all the way up to and including GAWR. And my max sidewall pressure is 80 PSI. To quote the manual under the Vehicle Loading section:

INFLATION PRESSURE
This is the cold tire inflation pressure for your vehicle
for all loading conditions up to full GAWR.

In every vehicle I've ever owned, including my last two trucks, the every day driving PSI was never more than about 60% of the max sidewall pressure. Even though everything I know tells me to drop the pressure to about 40 PSI, I can't lower the pressure more than 20% below what it calls for (which would be 60 front and 64 rear) or my TPMS will go off and the only way to reset it is to bring them back up to max PSI and start over.

My guess is, your manual reads the way it does BECAUSE of the TPMS and the fact it would sound warnings if you lowered the pressure to what it should be when unloaded. Its a catch 22 for the manual writers. Either put the correct info in the manual telling you to adjust the pressure depending on loading, and then have customers complaining that they cannot because of the TPMS warnings, or tell you to leave the pressure high, so the TPMS will not sound warnings, but have the truck ride like a lumber wagon most of the time.

My pressure placard calls for the front pressure to be 54 psi, which is about correct for the max weight on the front end for the tires I have. I'm sure your front end is quite a bit lighter, and am surprised that such a high pressure is called for.

Charles

 

[Onyrlef]

Probably not. Theres a temperature-pressure chart for that, and the mileage driven is irrelevant. Otherwise, check/fill when cold, it’s easier.

It’s not only easier, it’s the rule.

 

[Laura & Charles]

When we first got our TPMS I drove myself crazy trying to keep pressures as prescribed. On duals, the inside is always warmer EXCEPT when on the sunny side on a sunny day. I learned to become a lot more comfortable paying less attention to pressure and more to temperature… but becoming less waynal about the whole thing.

 

[Schultz]

Thanks for all the recommendations.
I also found Roger Marble's Blog (below link) that I found very helpful with almost any tire question.

An introduction to this blog and Roger Marble

We all have them. We all use and need them. But most would prefer to never have to think about them. As a Tire Design and Quality Engineer, ...

www.rvtiresafety.net

Thanks again,
Bob

 

[Ray-IN]

I replied to your post on the winneownerforum.com
Tireman9/Roger Marble says to inflate tires to 10-15% over those load/inflation charts, which show the absolute minimum air pressure to support the load. Those charts mean you are running your tires a 100% capacity all the time, with no reserve capacity. For comparison, auto tires normally have about 35% capacity.
I never have to be worried about this, I keep my tires inflated to the Federal Tire Placard listed pressures. I usually have to add air about 2X a year. Of course all tire mfgrs. advise to inflate tires to sidewall maximum listed pressure during long-term storage.

 

[Tulecreeper]

My guess is, your manual reads the way it does BECAUSE of the TPMS and the fact it would sound warnings if you lowered the pressure to what it should be when unloaded. Its a catch 22 for the manual writers. Either put the correct info in the manual telling you to adjust the pressure depending on loading, and then have customers complaining that they cannot because of the TPMS warnings, or tell you to leave the pressure high, so the TPMS will not sound warnings, but have the truck ride like a lumber wagon most of the time.

My pressure placard calls for the front pressure to be 54 psi, which is about correct for the max weight on the front end for the tires I have. I'm sure your front end is quite a bit lighter, and am surprised that such a high pressure is called for.

Charles

Doesn't matter why it is what it is. It is what it is, and I can't lower the pressure. Meh...

 

[Bobtop46]

For a class A you want this one.

https://www.amazon.com/gp/product/B0141KJTKQ/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1