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20-30 psi Tire Pressure Rise?


WisMonarch

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2004 Monaco Monarch

Greetings,

We are at the end of the first day of our first trip - in our new to us - first ever RV - from Wisconsin (-5F tonight) to Florida.  We are in Mt Vernon, IL tonight.
I put a TST TPMS system on and started with 100psi +/- in each tire.  The TST indicated that even with outside temperature in the 40s the front tire pressures went up 10-15psi and the rears went up 15-30psi as we drove.  With the inside tire of the dualies going up the most.  I had the cruise set between 65 and 67 for most of the day.  We're towing a 2005 Jeep Wrangler and its tire pressures went up from 32 to 34 as we drove.  The tires are new Continentals - I really don't want a tire failure.  So I have several questions:

1. Would you consider that pressure rise normal?
2. What would be the maximum pressure you would let the tires get up to before you let some air out?
3. Am I going to need to lets some air out when I get in hotter weather (hopefully in a couple days) and then put more back in when I return to the frozen tundra in four week?

It will be in the teens here in Mt Vernon in the morning so I don't want to let any air out here. 
We hope to be in Webster, Fl Sunday afternoon.

My signature has failed to post in the past so...
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Lee Cline
2004 Monaco Monarch - Ford F53 Chassis  "Monty"
2005 Jeep Wrangler LJ

 

 

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Tire and wheel manufacturers publish recommended cold pressures and make no mention of hot pressures, only to say never to let air out of a hot tire. Our steers (120PSI) get up over 145 in the summer, and they're 22.5". The tires on a Monarch IMO are going to be working harder.. If the tires are wearing OK and are not too hot to touch, run it and get used to what's normal. 👌

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Start with your coach's recommended pressures, or better yet weigh each corner and set pressures according to the tire manufacturer's load vs psi rating + a safety margin.  Personally I go 5-10 psi over.  Pressures are meant to be set cold and left alone. 

When the tire heats up that's normal.  If the tire is overloaded (too much weight or too little pressure) it will heat more. 

- bob

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Set your pressures cold and never let air out when they are hot. The manufacturers fully understand the temperature range the tire operates at. Set them at the cold pressure rating recommended for your weight, and that's it. The ONLY way you can set hot tire temperatures is if you have a pyrometer and are racing at Nascar, Indianapolis or racing motorcycles and have a great deal of experience. Ie, does not apply!

The 'best practices' route is to have all four corners weighed and then set each corner individually according to the weight on each corner. But never ever let air out of a hot tire to bring it down to the cold pressure rating. This will leave your tire dramatically under inflated. Keep it simple, set them cold, and the hotter they get, or work, the higher the rise will be. But know this, the manufacturer has taken all that into account.

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Thanks everyone for the wise council!  I want to get the four corners weighed but haven't figured out where to do that yet.

Any comments on the pressure equalization lines you can add that go between dualies? 
The outer ones run cooler and at a little lower pressure after they all come up to temp

JoeFromPerry - When you see an RV in site 441 after Sunday night, stop in and say Hi!  Oak Alley is where we are headed.  We have close friends in 440 we are meeting there.  I grew up in Castalia, Ohio, by Sandusky.  I drove through Perry many times.  Need I say it;  Its a small world...

 

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I like the idea of a Cat's Eye or Crossfire.. I bought a pair for my dually axle but never installed them. A good deal of the reason why is I had a leaking stainless hose valve extender, and had a commercial tire tech say that they're junk and recommended installing extended rigid valve stems, advice which I happily accepted. You're a step ahead with the TPMS and will never have to worry about a concealed flat. I think realistically there's always some scuffing between dual tires owing to difference in road crown, temperature, etc, but figure if it's a big concern, the big rig world would have fixed it.

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9 minutes ago, trailmug said:

I like the idea of a Cat's Eye or Crossfire.. I bought a pair for my dually axle but never installed them. A good deal of the reason why is I had a leaking stainless hose valve extender, and had a commercial tire tech say that they're junk and recommended installing extended rigid valve stems, advice which I happily accepted

Was your leaking extender the flexible kind that comes on coaches?  If so, I agree with the tire man, they are trouble waiting to happen.  I bought rigid all metal valve stems, not extensions, but one stem from the rim to the valve where the air goes in. They are formed to bring the end right out where they are right in front of you.           I bought from this place, not cheap but no leaks either.

 https://yourtireshopsupply.com/product/244/dlmonoco-oval-stabilizer-278in-178in-dlmonoco

Thay also have a rubber grommet to fit the odd hole in our rims that Monaco used.

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We've been using Nitrogen in our tires for years (22.5") on our 2004 Monaco Dynasty & we set the pressures when cold and never have had to adjust. Our TPMS says pressures don't vary enough to worry about.

 

Mike Harden

2004 Monaco Dynasty

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My tire only have 78% Nitrogen in them and a 10-15% increase in psi is normal on most days. Will see slightly more when it’s really cold when you start and if it’s a really hot day.

Most of my trips start with the temperature outside in the 70s and I do not adjust  the psi again even though the temp some mornings might be 50 or 80. I do put +5 over the the chart as I’ll still go with it 25 mph crosswind.

If I was starting a trip with it really cold out (going to be warmer) I’d only inflate to the chart psi. Once I get south I’ll have my +5 psi.

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  • 2 weeks later...

Thanks for all your thoughts and experience.  I feel much better about the tire pressure rise now.  So, Here's my plan.

The outdoor air temp was in the low teens when I left Wisconsin two weeks ago.  I had the cold tire pressure set at 100 psi on the recommendation of the place I bought the tires from.  (I haven't been able to weigh the four corners of my coach yet but will and then will fine tune the pressures.)  Its about 55F outside in Florida as I type this and the tire pressures are sitting at between 104 and 107 psi.

For the trip home leaving Florida in two weeks I'm going to set the front and rear dual outside tires to 102 psi.   Since the inside tire of the duals heated up and the pressure rose more than the outside, guessing because they get less cooling air flow and are closer to the brakes,  I'm going to set the inside tire pressures about 3-4 psi below the outside.  My theory is when the insides heat up they will close to equalize pressure with the outside tires.  I'll watch the tire pressures and if they get too low in the colder weather as I head north I'll add a little more air when they are cold.

BTW, there were originally extension hoses on one side of the coach dualies.  I looked at them before I left and one looked like it was almost warn through in one spot from rubbing on the edge of the rim.  I took them both off.  I'm guessing that's why the two were gone from the other side.

Best Regards,
Lee

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You are worried about the starting cold psi difference but won’t spend the $15 to weigh your axles at a truck stop to know where to start from?
You posted you had a 20-30 psi increase in a rear tire which tells me it was under inflated to start with… 15% increase is normal but not 25+%. Go weigh your rig!

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Most of what is said here is correct. I'll weigh in (no pun) with two points:

1. Getting axle-end weights cannot be done using the typical CAT scales found in truck centers. They measure weight of the truck's steer, drive, and trailer axles and add 'em up to get GVW. To know the weight on each steer tire, drive dually, and tag tire, you have to use a different scale--one that measures each of those four (or six) axle ends. As I mentioned in an earlier post, the Ramblin' Pushers Maintenance Session* (Goshen, Indiana 4/27/2022 to 5/5/2022) has a two-pad truck scale that can measure individual axle ends. The driver is given the reading and a worksheet used in a technical seminar on tires to determine the proper inflation for each axle (not axle end). Each tire on the axle must have the same cold pressure and that is the pressure for the axle end that carries the greater load. Truck center scales see the average weight of each axle which can result in one axle end being under inflated. That said, if you have to use a truck center scale, it's better than nothing.

2. Another important point not seen in this discussion is the ambient temperature when when setting cold inflation pressures. I learned about this in the mountains of Colorado and New Mexico. At the start of the day in Durango, CO, I set the pressure to my cold pressure of 100 psi. It was a brisk October morning in Durango, temp was in the 30s. When we got to Santa Fe, the TPMS high pressure alarm went off.  We got off the highway and let the tires cool while we had lunch. By the time we got to Albuquerque, NM, the TPMS alarm was beeping again. We stopped twice more before we reached our destination. As you might guess, the my tires were overinflated. Letting them cool overnight I checked them again the next morning and adjusted the cold inflation to once again be 100 psi.

What I didn't know in Durango I learned in Albuquerque. Cold tire pressures must be corrected for ambient temperature. The standard temperature for cold inflation is 65°F. One of the folks we met in Albuquerque gave me a Temperature/Pressure Correlation Chart consisting of a matrix of temperatures (rows) and pressures (columns) with the 65° row highlighted. To use the chart, first check the ambient (outdoor) temperature and then find the corresponding row (temp) and specified pressure (column) on the chart. The intersection of those two shows the cold pressure adjusted for temperature.** The next thing we did was buy four new 275/80R 22.5 LRH tires for the drive axle.

Here is the Temperature/Pressure Correction chart I use. Others can be found on tire manufacturers websites. None I have seen vary significantly from this one.

I hope this helps others travel safely knowing that their tires are inflated properly. 

Anyone want to talk about Tyron bands?

 

Roger Smalley 2006 HR Endeavor PDQ

*See www.ramblinpushers.org for more details.

**The axle weights (and cold inflation settings) may vary by axle.

SmarTire Temp & Pressure Card.pdf

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Ivylog - Can you suggest places I can get the four corners individually weighed?  I'm new at this and I don't know where to start looking for that.  If I can't get four corners I guess I'll just use a CAT scale.

I really did not think I would be under aired at 100 psi on each tire - but maybe?  I thought setting the cold pressure when the outside temp was single digits or low teens and driving into temperatures in the 60s or 70s might have something to do with the pressure rise.

Thanks for weighing in.  No pun intended.
Best Regards,
Lee

 

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On 3/1/2022 at 5:08 AM, WisMonarch said:

For the trip home leaving Florida in two weeks I'm going to set the front and rear dual outside tires to 102 psi.   Since the inside tire of the duals heated up and the pressure rose more than the outside, guessing because they get less cooling air flow and are closer to the brakes,  I'm going to set the inside tire pressures about 3-4 psi below the outside.  My theory is when the insides heat up they will close to equalize pressure with the outside tires.  I'll watch the tire pressures and if they get too low in the colder weather as I head north I'll add a little more air when they are cold.

Please don’t do that. All the tires on a given axle should be inflated the same, including the drive axle. Yes, the inside duals might see a small difference from the outers, the same as if the sun is intensely shining on one side of the RV. Tire manufacturers have figured this out long before we came around. Follow manufacturer guidelines: inflate to recommended Cold (actually “not driven yet”) Inflation Pressure (aka “CIP”) at the start of each driving day and leave it alone.

When I first got a TPMS (SmarTire, which actually goes inside the tire not on the valve stem), I started to freak out about high temperatures in extremely hot (110°+) weather. I was seeing 150°+ on the inner duals. I talked to the Michelin and Goodyear reps at the next FMCA rally. They were attentive and polite, and the essence of the response was, “Yes, that’s normal. We proof the tires at up to 300° during manufacturing. Leave the tire engineering to us, follow inflation recommendations, and drive on”.

What I’ve come to realize over the years is that inflation, not temperature, is the key factor, and that you’re best approach to a TPMS is to look for anomalies, not absolutes. Any given TPMS is only going to approximate in accuracy, especially at the extremes. Valve stem mounted sensors won’t be as accurate as ones mounted on the rims. What you’re really looking for is that one tire that’s suddenly running high or low on pressure, different from all the rest and from what you normally see given conditions. That’s when you know you have an issue, even (hopefully) before an alarm sounds.

Bottom line: don’t over think this, follow recommendations, and drive on…

Hope this helps,

Edited by georgecederholm
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12 hours ago, WisMonarch said:

Ivylog - Can you suggest places I can get the four corners individually weighed?  I'm new at this and I don't know where to start looking for that.  If I can't get four corners I guess I'll just use a CAT scale.

I really did not think I would be under aired at 100 psi on each tire - but maybe?  I thought setting the cold pressure when the outside temp was single digits or low teens and driving into temperatures in the 60s or 70s might have something to do with the pressure rise.

Thanks for weighing in.  No pun intended.
Best Regards,
Lee

 

Four corners is obviously more accurate, but just weighing each axle will get you pretty close. You can weigh all corners on the cat scale but you'll need several weights and need to do it when there are no truckers waiting.

You're acting like the pressure being too high might be a problem and you want to limit the pressure increase. Tire pressure being to high is not a problem and will only make the ride a bit harsher.

Tire pressure rises because the air inside the tire heats up. What causes it to heat up? The tire flexing and dissipating energy causes it to heat up. So the lower the tire pressure, the more the tire flexes... tire heats up and then the air inside heats up. If the heat gets past a certain level the tire will delaminate and come apart. 

Yes, the inside dual will get hotter than the outside dual, and will have a little more pressure rise... and that doesn't matter. Like others said... set the tire pressure by weight and don't overthink it.

And don't worry about your tire pressure being too HIGH... worry about it being too LOW. Err on the high side. That hack at the tire store doesn't know how much load is on your axles. But there's a sticker behind the drivers seat that will show you the axle weights at full load. Then you can get on the tire manufacturer's website and see how much pressure they recommend at that load.

Then once you've weighed the rig, you can adjust the pressures based on the scale.

Cheers,

Walter

Edited by wamcneil
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13 minutes ago, Bob Jones said:

Or you could just make it easy on yourself and read the tire placard in the vehicle and run those pressures with the tire cold and leave it alone. 

Almost as easy as just running the CIP embossed on the tire sidewalls.

Assuming the tires match the OEM spec… 🤔

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11 minutes ago, georgecederholm said:

Almost as easy as just running the CIP embossed on the tire sidewalls.

Assuming the tires match the OEM spec… 🤔

One thing's for sure, no-one can make something more complicated than an RV'er 🙂 

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Thanks Bob.  I've been overthinking this and trying to decide whether I want to do a TPMS.  I'm having Borg valve stems put  on tomorrow, thanks to a recommendation on this forum.  This will ease checking pressures before I drive and eliminate the flexible extensions.  I will run the recommended pressures on the chassis tag by the front seat.  We do get wrapped around the axle sometimes!!

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24 minutes ago, 96 EVO said:

CIP ?

Sorry! I thought I noted this in a prior post. “Cold Inflation Pressure”. “Cold” meaning ambient, not driven on, not overly warmed by the sun. Actually, it’s probably stated “Max PSI” on the sidewall, which is extra misleading since that’s the minimum cold inflation pressure for the maximum rated load of the tire for the axle type (single or dual). 🤪

Maybe it’s the tire engineers and regulators who can actually make things more complicated than the RV crowd? 😂

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It is funny the way it works sometimes. I tried different pressures on mine and, in the end, it turned out the best ones to use were on the tires placard behind the driver's seat the entire time. Go figure 🙂 I'm pretty Monaco sat down, did the homework, took into account typical tank levels and weights to come up with their recommended number. 

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Oh, I wouldn't run max inflation pressure! 

That would put 130psi in my drive axle and  tag axle tires, when they only need 85psi and 80psi to carry the maximum load the axles are rated for.

It would feel like riding in the Flintstone mobile!

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