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Old 06-26-2015, 07:23 PM   #1
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Class A tire pressures


We have a 2000 40' Country Coach Intrigue.

We always start each trip by driving 5 miles to Les Schwab to get the tires checked while the tires are still cold.

I've discovered that all the Les Schwab dealers don't set the "cold tire pressure" at the same PSI.

I discovered this by having Les Schwab dealer in Oregon install a new TPMS (Pressure Pro with the new Pulse Display). The TPMS works off a "Baseline tire pressure" which is the PSI when the sensors are installed. The alarms are then triggered if the PSI or temp changes 25% from the baseline PSI. This is the factory default.

We had the dealer in Oregon check the PSI in all 6 tires after driving about 1.5 blocks. Once on I-5 the high pressure alarm went off showing a PSI of 127. Mean while the coach rode like a board with no shocks.

So, here is my question- what should the cold pressure (baseline) be?
What should it be once underway at freeway speeds.

I know that this is dependent on the ambient air temperature and roadway temperature.

I'm looking for some guidelines here not exact measurements just some ideas what others are seeing.

By the way, my local Les Schwab dealer told me this morning that my cold PSI should be between 100-110 PSI.

Thanks for your thoughts.
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Old 06-26-2015, 07:45 PM   #2
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I don't know exactly what the cold base line is, I think 67-68 degree. As temperatures go up the psi go down for the cold psi check.

You should have a sticker somewhere in your coach, probably near the drivers seat on the wall, that has the recommended psi for front and back based on the weight of the vehicle.

My recommended pressures are 85 rear and 95 front. I run mine about 10psi over. I do this to make sure they are not under inflated.


Last August I had to install a new TPMS sensor so I went to the trouble of setting all the pressures. This reestablished the baselines for each sensor. Last month prior to a trip in May all the pressures were right where I sent them 9 months earlier.
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Old 06-26-2015, 07:56 PM   #3
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Your tire pressure will depend on the weight of your coach and the tires you have on it.

Get the 4 corner weight of your coach fully loaded including people and then find the inflation chart for your tires.

My opinion of having a dealer check your tire pressure is not very high. Usually they have the low person on the pay grade doing the checking. Tire pressure should be checked every morning before they are warmed up.

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Old 06-26-2015, 08:52 PM   #4
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We would have to have the coach weight front and rear minimum Plus the type and size tires that you have to suggest an air pressure.
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Old 06-26-2015, 09:13 PM   #5
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sounds like you have a pressure sensor for your tires set the pressure one morning with out moving the coach then check before each drive with your monitor only. the tire pressure will be higher on the side towards the sun but all should be within a few lbs of each other don't fett small changes in you tires as you drive the pressures will equalize. if you go to a higher elevation and stay there for an extended time you might want to change the pressures. sounds like you drive to some where to set the pressures by the time you get there your tires are hot so your cold pressure is way off.
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Old 06-26-2015, 09:41 PM   #6
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Originally Posted by jacwjames View Post
I don't know exactly what the cold base line is, I think 67-68 degree. As temperatures go up the psi go down for the cold psi check.

You should have a sticker somewhere in your coach, probably near the drivers seat on the wall, that has the recommended psi for front and back based on the weight of the vehicle.

My recommended pressures are 85 rear and 95 front. I run mine about 10psi over. I do this to make sure they are not under inflated.


Last August I had to install a new TPMS sensor so I went to the trouble of setting all the pressures. This reestablished the baselines for each sensor. Last month prior to a trip in May all the pressures were right where I sent them 9 months earlier.

Almost.

There is no "baseline" temperature. This is a common misunderstanding left over from Chem lab where certain experiments were to be run at "Lab Standard"

For tires 'Cold" inflation means when the tires are at ambient temperature and not warmed by being in direct Sunlight and are not warmed by being driven more than a mile of 2 (5 is too much).

The tire inflation sticker has the inflation the RV company provides based on their guess on how much "stuff" you will be carrying. While this might be OK for a starting point it may not the real correct number.


jafran304 is correct about needing to know the actual load on each tire position. Just axle load is not always good enough as very few RVs have 50/50 side to side weight distribution. being out of balance by 1,999# is not unusual.

Now until you can learn your actual individual tire position loads you can get an axle reading at many large truck stops on the Interstate. With the numbers you get there you should assume you are no better than 47/53% so use the 53% figure to look up the proper inflation.

Here is a blog post showing the steps in a real life example. There a number of posts with "Weight" "Load" and "Inflation" as labels. I suggest you review them.
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Old 06-26-2015, 09:49 PM   #7
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Quote:
Originally Posted by JOC1212 View Post

We have a 2000 40' Country Coach Intrigue.

We always start each trip by driving 5 miles to Les Schwab to get the tires checked while the tires are still cold.

I've discovered that all the Les Schwab dealers don't set the "cold tire pressure" at the same PSI.

I discovered this by having Les Schwab dealer in Oregon install a new TPMS (Pressure Pro with the new Pulse Display). The TPMS works off a "Baseline tire pressure" which is the PSI when the sensors are installed. The alarms are then triggered if the PSI or temp changes 25% from the baseline PSI. This is the factory default.

We had the dealer in Oregon check the PSI in all 6 tires after driving about 1.5 blocks. Once on I-5 the high pressure alarm went off showing a PSI of 127. Mean while the coach rode like a board with no shocks.

So, here is my question- what should the cold pressure (baseline) be?
What should it be once underway at freeway speeds.

I know that this is dependent on the ambient air temperature and roadway temperature.

I'm looking for some guidelines here not exact measurements just some ideas what others are seeing.

By the way, my local Les Schwab dealer told me this morning that my cold PSI should be between 100-110 PSI.

Thanks for your thoughts.

25% pressure loss is too much. If you don't start looking for a place to pull off before that you have a good chance of doing damage to your tires.

My TPM are set to warn at 10% below the minimum cold pressure needed to carry the load. My system also has a "rapid air loss" feature which means if I loose more than 3 psi from the higher hot pressure in less than a few minutes I will get a warning.

Example My cold is 70 My low warning is 62. My normal hot pressure is bout 79. If my hot drops to 75 in just a couple of minutes or so I will get a warning. This allows me to monitor the pressure loss while the co driver and I look for a safe place to pull over. Hopefully the rate of air loss from the puncture will only be a few psi per minute so I might have 5 minutes to find a safe place to pull over and may not have dropped the hot pressure to below 65 so other than the nail hole I probably have not damaged my tire.
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Old 06-26-2015, 10:20 PM   #8
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Bottom line is you should learn to check your tire pressure yourself instead of depending on Les Schwab. And check your tire pressure every morning before leaving at campground either with your monitors or a tire gauge.

You are responsible for your own family safety, not Les Schwab
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Old 06-26-2015, 11:02 PM   #9
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I will concur with the statements about letting a tire dealer check your tire pressures. Last week I had Fletcher's Tire in Mesa, AZ install 6 new Hankook AH11's on my Fleetwood Fiesta Class A. I asked them what they set the pressures at, at they told me "they always set them at 100 psi." Well, that is my personal max, as the placard in the RV states 80, so I have always allowed an extra 10 lbs. or so since I never have had the RV weighed, yet. And, it's always easier to let air out than put it back in.

Anyway, getting back to the story, after I paid and did a quick walk-around, I noticed one valve stem cap was missing. I pointed it out, and it got replaced. By the time I got back to my storage facility, 5 miles away, two more were missing, and a third one was about to fall off.

I stopped by the storage place today to do some preparation for a 3700 mile trip coming up soon, and noticed a tire that seemed a little low. Out came the pressure gauge, and the 6 tires showed readings of 73, 58, 90, 70, 18 and 72. Went home and got the air compressor, topped them all up to 90, and by the time I was done, the 18 psi tire was back down to 78 (from 90), and the 58 psi one was back down to 84 (also from 90). I tightened the valve stem down in the core three quarters of a turn in both of them, and will see what readings I come up with tomorrow.

Real pleasant 2 hour experience, in 114 degree heat, with RV's parked so close together that you have to lay on your side to even get the side compartment doors open to get an extension cord to run your 80 lb. compressor off your generator!! All this after giving Fletcher Tire $2047 last week.

Okay, I'll quiet down, now.
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Old 06-27-2015, 12:52 AM   #10
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I got a new set of Michelin 295/80R22.5 XZA2 and had my coach weighted at the FMCA Rally in Albany,Or (4 corner wt) and I'm over wt in the rear by 1150lbs and under in the front by 730lbs. They said to moved some heavy stuff from the rear bay to the front bay to get a better wt. reading. With a combined wt of 33,620lbs FR 6,405lbs-FL 6,065lbs RR 10,195lbs-LR 10,955lbs I have to run 105 PSI in the front and 100 PSI in the rear. They give you a print out of your coach wt's and the air pressure to run. This is the only way to get a true wt reading and know what PSI to run, money well spent. Must be the new steel and brass radiator to be over on the LR and not the way the wife packed the coach
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I run the TST tire pressure system on the coach and toad works great.
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Old 06-27-2015, 12:53 AM   #11
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Class A tire pressures

Our coach runs at max gross weight all the time. Based on corner weights from Jan '14, I run 110psi front, 95psi rear. My tires also seem to gain a fair bit of pressure at highway speeds. I've set my upper limit triggers at 130psi front and 115psi rear. After a while at highway speed my fronts are holding at about 128 lbs and the rears at 108-110 lbs. Tire temps seem moderate; I don't know why my pressures increase as they do. My low triggers are set at -10psi (100 front and 85 rear).



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Old 06-27-2015, 08:35 AM   #12
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Our coach runs at max gross weight all the time. Based on corner weights from Jan '14, I run 110psi front, 95psi rear. My tires also seem to gain a fair bit of pressure at highway speeds. I've set my upper limit triggers at 130psi front and 115psi rear. After a while at highway speed my fronts are holding at about 128 lbs and the rears at 108-110 lbs. Tire temps seem moderate; I don't know why my pressures increase as they do. My low triggers are set at -10psi (100 front and 85 rear).
Fulltiming since '12 2002 DSDP 40, FL, Cat 3126
You say your temperatures are "moderate" Could you provide some numbers? It would if you could also give the approximate ambient at the time of day you are giving us the tire temperature.

If the air used to inflate your tires came from a shop that did proper maintenance on their air compressor the air should be dry enough to have the pressure increase due to temperature to be in the 2 or 3 % for 10F increase. However if the tires were inflated using "wet air" that you can get when the shop forgets to drain their tank or there is a malfunction in the air dryer then you could have a lot of moisture in the tire air which could result in a greater increase in pressure.

Next time you have access to air you might try pulling the valve core from one of the duals for maybe 5 to 8 seconds. Do you get drops of water spitting out? or does frost form on the end of the valve? If so you need to try and get the air changed in your tires.

Now I know an "air change" sounds like some scam to help lighten your wallet but what we are trying to do is to remove excess moisture from your tires. You can't just pull a valve core and let all the air out as the tire would deflate and probably de-seat from the wheel which could damage the tire. The suspension needs to be supported. It is also not a good idea to completely de-flate your tires more than 50% as when inflating a tire from zero psi is not a good idea and for large tires (19.5 & larger) it's considered unsafe to inflate tires from zero outside a Safety cage.

I don't think that too much moisture in your tires is really a safety issue but the moisture can boost the hot pressure making it difficult to properly monitor hot inflation. Moisture could result is corrosion of the wheel and excess moisture is not good for the tire structure as it is possible for the high pressure to drive water molecules into the tire structure which might result in corrosion of the steel body or belt plies.

Before you start the "Air Change" lets confirm you really have the problem. Let me know the numbers and I will be happy to work with you.
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Old 06-27-2015, 11:05 AM   #13
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Quote:
Originally Posted by JOC1212 View Post

We have a 2000 40' Country Coach Intrigue.

We always start each trip by driving 5 miles to Les Schwab to get the tires checked while the tires are still cold.

I've discovered that all the Les Schwab dealers don't set the "cold tire pressure" at the same PSI.

I discovered this by having Les Schwab dealer in Oregon install a new TPMS (Pressure Pro with the new Pulse Display). The TPMS works off a "Baseline tire pressure" which is the PSI when the sensors are installed. The alarms are then triggered if the PSI or temp changes 25% from the baseline PSI. This is the factory default.

We had the dealer in Oregon check the PSI in all 6 tires after driving about 1.5 blocks. Once on I-5 the high pressure alarm went off showing a PSI of 127. Mean while the coach rode like a board with no shocks.

So, here is my question- what should the cold pressure (baseline) be?
What should it be once underway at freeway speeds.

I know that this is dependent on the ambient air temperature and roadway temperature.

I'm looking for some guidelines here not exact measurements just some ideas what others are seeing.

By the way, my local Les Schwab dealer told me this morning that my cold PSI should be between 100-110 PSI.

Thanks for your thoughts.

I know that some TPMS set the "baseline" pressure for each tire based on the pressure in the tires when first installed. Others I believe allow you to "set" the baseline pressure through controls on the TPM display. Suggest you read the instructions and learn the procedure for your unit.

Lot of guessing here but it seems the baseline pressure may not be set correctly or is set too low.

Really need the numbers from you and others with similar problems before informed advice can be offered.
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Old 06-27-2015, 11:11 AM   #14
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I installed my Hawkshead TMPS and am very happen with it. My cold ambient air pressure front is 100 psi and 95 rear. After driving 20 minutes starting ambient temp is 68and tire temp increases to 85 and the tire psi front to 115 and reared to 110. All tires increase consistent amount. So 17 degrees increase shud be approx 8 psi increase but mine is double that? My buddy purchased the same TMPS and is tire pressure increase are consistent with mine. I'm not concerned as my increases are consistent for each tire. But are you saying that I have excessive moisture in my tires?
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