Tire Pressure

[Dlvgolf]

I just need a sanity check. I read about everyone running their tires at 113, 115, 103, etc psi. A lot of tire pressures over 100. On the sidewall of all my tires it says “cold psi 115”. However, the RV sticker says 82. I’m not misreading this right? I mean, I’ve been driving for almost 50 years and reading PSI stickers for that long, so I think I know what I’m looking at. It’s just that my numbers are SO different from everyone else’s, that I’m afraid I’m having a senior moment.
Thanks for the help.

[Goodspike]

Your tire probably says max pressure 115, or 115 for maximum weight. Personally I'd adjust based on the weight you're carrying, and also how the vehicle handles (oversteer/understeer, ride, etc.), going no lower than 82 or higher than 115, also paying attention to the load you are carrying and how close that is to the tire ratings.

[ThomB]

Everyone should probably be running at different levels based on the weight. I run at 88psi all around which may not be correct for the weight but what I've done the entire time we've owned the rv (recommended by the previous owner). The fronts will run themselves up to about 105 during normal driving. Setting them to the max would scare me.

[Goodspike]

Originally Posted by ThomB

The fronts will run themselves up to about 105 during normal driving. Setting them to the max would scare me.

I assume you mean they heat up and increase pressure to 105. The tires would probably heat up fewer degrees (but not necessarily a lower temperature) with higher cold pressures since there would be less sidewall flex.

Also the max pressure stated on the tire is a cold pressure, so they contemplate it going higher.

[Morich]

For a very long time I was one who thought getting tire pressure right and checking to adjust to keep it right was a very important item but I now find I was wasting a lot of time and chasing an item which I can't catch!
I find there are specs for pressure and I do keep aware of them but getting more info on what my tires do as I drive by using a tire temperature and pressure monitor system (TPMS) has changed my outlook a great deal.
We check the specs, figure the weight and adjust it all very precisely but then if we don't know what happens as we drive, what value does that have? It is an estimate of what the tire does under "normal" conditions.
What I find is that the "normal" is often not what my tires are doing!
My monitor sets alongside of me and tells me temp and pressure of each tire and I can see that small things mean a lot to tire temp, which also changes pressure. When it sets in the yard, I can see which tire gets sun or shade as the temp and pressure change!
When I drive, the inside right rear dual runs hotter than the outside. The crown or shape of different roads puts more weight on inner than outer duals at times. There is also an exhaust running past this tire.
Bottom line for me was spec said 82 but it never stayed there anyway for more than thirty minutes of driving, so I've backed off to 75 as a nice round number and find it rides better as the pressure certainly goes up as I drive.
I tried using nitrogen as it was promoted as a way to cut down the pressure change due to temp but found it nearly meaningless and research shows the normal air is 78 % nitrogen already and much, much, cheaper! It may work for Indy racers but I don't see it practical for RV.
Rather than worry about the specs, I now favor getting a monitor that tells you what is actually happening at all times and lets you know if it varies from normal as normal is a whole lot more important that spec.

[Dlvgolf]

Originally Posted by ThomB

Everyone should probably be running at different levels based on the weight. I run at 88psi all around which may not be correct for the weight but what I've done the entire time we've owned the rv (recommended by the previous owner). The fronts will run themselves up to about 105 during normal driving. Setting them to the max would scare me.

Yeah, set at 82, mine run up to 99, sometimes as high as 103 in the summer. That’s why setting them higher was bothersome to me.

[Goodspike]

Originally Posted by Morich

We check the specs, figure the weight and adjust it all very precisely but then if we don't know what happens as we drive, what value does that have? It is an estimate of what the tire does under "normal" conditions.
What I find is that the "normal" is often not what my tires are doing!
My monitor sets alongside of me and tells me temp and pressure of each tire and I can see that small things mean a lot to tire temp, which also changes pressure. When it sets in the yard, I can see which tire gets sun or shade as the temp and pressure change!

The specs are a cold tire pressure--it doesn't matter what they are at other times as long as they are not leaking.

Same with engine oil levels. Some are designed to be checked hot. My truck is designed to be checked after it has sat at least 8 hours. What it is when the engine is running or other times not called for when checking is not something you should monitor (but I have found that the low engine warning on Subaru engines is surprisingly precise to the dipstick).

Same with transmission fluid levels. Those typically have rather involved instructions on how to test.

[Dlvgolf]

Originally Posted by Morich

For a very long time I was one who thought getting tire pressure right and checking to adjust to keep it right was a very important item but I now find I was wasting a lot of time and chasing an item which I can't catch!
I find there are specs for pressure and I do keep aware of them but getting more info on what my tires do as I drive by using a tire temperature and pressure monitor system (TPMS) has changed my outlook a great deal.
We check the specs, figure the weight and adjust it all very precisely but then if we don't know what happens as we drive, what value does that have? It is an estimate of what the tire does under "normal" conditions.
What I find is that the "normal" is often not what my tires are doing!
My monitor sets alongside of me and tells me temp and pressure of each tire and I can see that small things mean a lot to tire temp, which also changes pressure. When it sets in the yard, I can see which tire gets sun or shade as the temp and pressure change!
When I drive, the inside right rear dual runs hotter than the outside. The crown or shape of different roads puts more weight on inner than outer duals at times. There is also an exhaust running past this tire.
Bottom line for me was spec said 82 but it never stayed there anyway for more than thirty minutes of driving, so I've backed off to 75 as a nice round number and find it rides better as the pressure certainly goes up as I drive.
I tried using nitrogen as it was promoted as a way to cut down the pressure change due to temp but found it nearly meaningless and research shows the normal air is 78 % nitrogen already and much, much, cheaper! It may work for Indy racers but I don't see it practical for RV.
Rather than worry about the specs, I now favor getting a monitor that tells you what is actually happening at all times and lets you know if it varies from normal as normal is a whole lot more important that spec.

I’ve actually considered starting lower, since my pressure and temps starts going up almost immediately (I too keep my TPMS monitor in eyesight while driving). My inside driver hits 99 before any of the other tires, but seems to top out at about 100, no matter how long I drive. During the 110 heat of the summer, it got up to 109. Then I got to thinking that if the mfg tells me 82 cold, they prob know it’s going to end up at 99-100 and that’s where they think I should be running. By going lower am I second guessing the experts!?!? It makes my brain hurt.

[Goodspike]

Originally Posted by Dlvgolf

Then I got to thinking that if the mfg tells me 82 cold, they prob know it’s going to end up at 99-100 and that’s where they think I should be running.

They definitely know.

By going lower am I second guessing the experts!?!?

Yes, and you're also creating an unsafe condition making it more likely you'll have a blowout.

Realize that before these tire pressure monitors many people had no idea what their pressures were while driving. Sometimes too much information is not better.

[Wyatt]

I think the best explanation I’ve received in regard to the same question was from a poster named tireman. He appears to be an expert in the field of tires. I’m posting a link to a similar thread where he answered my very same question. As well as a screenshot from the specific post he answered.
https://www.winnieowners.com/forums/...ns-355847.html

[sundog964]

Originally Posted by Goodspike

The specs are a cold tire pressure--it doesn't matter what they are at other times as long as they are not leaking.

Same with engine oil levels. Some are designed to be checked hot. My truck is designed to be checked after it has sat at least 8 hours. What it is when the engine is running or other times not called for when checking is not something you should monitor (but I have found that the low engine warning on Subaru engines is surprisingly precise to the dipstick).

Same with transmission fluid levels. Those typically have rather involved instructions on how to test.

When I race, my cold pressures are about 28 psi on the Porsche, the heat into the tires gets them to about 36-37. Any higher and the R-Compound tires are like driving on ice.

I'm not contemplating taking my Vista down the straight at 140 MPH though, so it should just be a pressure that is good for driving. With so much sidewall, you do want to have a high pressure so that there is less flex involved when driving and turning.

Ours came at 90 PSI from the dealer, and I think I'll bump them up about 5 PSI just because of the way they flex when sitting. And some oversteer which can be quite unsettling, as the Porsche does the understeer thing, so not used to it in my vehicles.

Now if I could just Toad the Porsche!

[Wildman]

I have watched many conversations about tire pressures. I believe that if you weight your vehicle by axle, then go online and you will see tire size, and weight charts to apply to yours. Mine is approximately 3600 lbs per tire. Chart calls for 80psi for a 245 x 70 x 29.5 (made after 2008). ThIs keeps the tire patch even and more consistent wearing.

[jerichorick]

Originally Posted by Dlvgolf

I just need a sanity check. I read about everyone running their tires at 113, 115, 103, etc psi. A lot of tire pressures over 100. On the sidewall of all my tires it says “cold psi 115”. However, the RV sticker says 82. I’m not misreading this right? I mean, I’ve been driving for almost 50 years and reading PSI stickers for that long, so I think I know what I’m looking at. It’s just that my numbers are SO different from everyone else’s, that I’m afraid I’m having a senior moment.
Thanks for the help.

My two cents.
Pay attention to these folks. They have posted some great stuff here. This is my summation of this topic:
1/ Do a 4 point and axle weighing of your rig.
2/ Per manufactures pressure guide, set your axle tire pressure at the spec for the heavy wheel. Never adjust this setting when the tires are hot from driving or sun.
3/ Setting the tires a couple of pound over chart spec never hurts. Under is not a good idea.

4/ Keep dry air in the tires. (I use a air dryer on my pancake compressor.) High humid air expands more than dryer air as it heats.
5/ Tires are only good for about 7 to 10 years.
6/ Sidewall cracking is common for Michelin. That's why I don't use them.
I think that just about covers the major issues of this topic with some add-ins.
Happy and safe trails,
Rick Y

[Morich]

We could still get into what "cold " pressure means! When living in cold country, we thought of cold as being somewhere freezing or below but down here we begin to think it's getting cold when you need a long sleeved shirt!
What the tire folks mean for cold is still not real clear for all the parts of the country where we drive.
I've reached the point of being willing and able to buy a new set of tires every five-ten years if it means I don't have to sweat over the pressure every day!

[jerichorick]

Originally Posted by Morich

We could still get into what "cold " pressure means! When living in cold country, we thought of cold as being somewhere freezing or below but down here we begin to think it's getting cold when you need a long sleeved shirt!
What the tire folks mean for cold is still not real clear for all the parts of the country where we drive.
I've reached the point of being willing and able to buy a new set of tires every five-ten years if it means I don't have to sweat over the pressure every day!

Good point Richard. Another way to think about cold psi is type of travel. Regional temperatures tend to swing withing a moderate range so daily tire checking is not as critical. For long haul, the ambient temperature can range widely in a single days travel.
Here is a bit of confusion stimulation for you: https://www.vehicleservicepros.com/v...20120%20psi%29.
With this information why are we so worried about the cold psi today if it is 5 psi lower than yesterday when the ambient temperature is 10* cooler this morning? Peace of mind? Manufactures load chart ratings?
Happy trails.
Rick Y