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Recommended Tire Pressure

Yahoo Message Number: 71874
I'm replacing all eight tires on my 2004 Allure Newport (40' with tag axle). The new tires will be the same as the old: TOYO M111z 12R/22.5.
Here's the question: What do I tell the tire dealer to inflate the to?
My SMARTire (which is still working) shows the two front tires to be at about 100 psi when cold, then they go to about 110 when hot. Similarly, the rear duals start out at 90 and get to about 100 when hot. Does that square with the experience of other CC owners?

Thanks in advance for your input.

Jim Mercer
Albuquerque

2004 Allure Newport, 31070

PS- Is there any sense in trying to "refuel" the SMARTire sending units at the same time? Manual says they are good for 7 yrs or 90,000 miles and are nonreplaceable. I've about decided to just get a Tire-Stem Cap model when the SMARTire craps out unless someone has a better idea.

Re: Recommended Tire Pressure

Reply #1 –
Yahoo Message Number: 71877
Jim This is a topic that has been beat to death. According to FMCA, the proper tire pressures are suggested to be set according to the Weight/Pressure tables by the tire manufacturer. It therefore a necessity to weigh the coach at all the wheels with your typical loads. The manufacturers , obviously , build a safety factor into their numbers in theses charts, but most people will add 5 to 10 PSI into the pressures, because they may change the weight they carry. I personally add 5 PSI to the figure from the chart. This is a good time to see how close one is to the weight carrying capacity of each axle. The COLD pressure is the only pressure to be concerned about as this is the basis of the manufacturers recommendation. The subsequent pressure when hot is not of consequence, as that is figured into the manufacturers tables. The coach manufacturers usually put recommended pressures on the labels of the coaches , higher than required , to cover their a_ _ , because of the Firestone/Ford lawsuits. You will hear all sorts of other opinions, but this is certainly, the consensus from this forum.

Ron Baran 09 Magna 7025

Re: Recommended Tire Pressure

Reply #2 –
Yahoo Message Number: 71881
Another thing to remember, "cold" means the tires must be at rest for several hours and out of the direct sunlight. For example, if your tire pressure should be 100#, then they should be at that pressure no matter the atmospheric temperature whether in Fargo ND at 60 degrees or Yuma AZ at 95 degrees.

Jim E

Re: Recommended Tire Pressure

Reply #3 –
Yahoo Message Number: 71884
I'm not sure I agree with your comment Jim. As I understand it, if 100 PSI is the ideal pressure, then you set the tire(s) to 100 PSI at around 70 degrees air temperature with the tires at rest at that temp for a number of hours.
Pressure changes by about 2 PSI for every 10 degrees, either up or down. As at Fargo ND at 60 degrees ambiant you'd set the tires to 68 PSI. In Yuma AZ at 95 degrees, you'd set them to 105 PSI.
So you set them correctly once and don't fiddle every time the air temperature is different.

Lee
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Lee Zaborowski

07 Intrigue 12153, Cat C-13

Re: Recommended Tire Pressure

Reply #4 –
Yahoo Message Number: 71888
Jim, cold refers to temp before driving.

Lee with all due respect .....setting your tire pressure at 68 psi would not be recommended with load factor, let's say on the front axle. 22.5 on a 8 or 9 inch wide tire. At least this is how I read your Fargo sentence.

AL

Re: Recommended Tire Pressure

Reply #5 –
Yahoo Message Number: 71889
Lee,

That's what I used to think. In fact, I had a chart, that I downloaded from the internet, showing minimum pressures at different temperatures. If I remember correctly, the standard temperature was 69 degrees. The lowest temperature on the chart was about 60 degrees and stated to never lower your tire pressure below that corresponding pressure. The highest temperature was something above 100 degrees. Again, if i recall correctly, the pressure differential was less than 10# from 60 to 100 degrees.
Following this subject on several forms, it became more confusing to me so i sent an email to a tire manufacturer, Bridgestone if I recall correctly, asking them for clarification. There response was as I stated in my previous post. The tire load limit charts from all the tire manufactures web sites do not specify temperatures except they should be cold. They do not define cold. That's why I asked Bridgestone for clarification.

Jim E

Re: Recommended Tire Pressure

Reply #7 –
Yahoo Message Number: 71893
Quote from: James"

Lee,

Check your math. I think you had fat fingers when you said set the PSI to 68 degrees. Never, never 68.
Lyle Wetherholt
04 Intrigue 11740

Re: Recommended Tire Pressure

Reply #8 –
Yahoo Message Number: 71895
Jim, there are so many variables, one PSI number does not apply to all circumstance. The only rule I worry about is not exceeding the max PSI for the rim at cool (69 F, 70 F, whatever . . .a toss up).
One guideline I believe in and many use is to determine your best PSI at 70 F, then add 10 PSI as a safety margin, as long as you don't exceed the maximum rim PSI. My ideal front PSI is 95, I run 105.My rims are good for 125 PSI.
For your comfort Jim, then if you go 10 PSI over the ideal at 70 F, you'd have to get down to 20F to get down to you recommend ideal PSI.

Lee

Re: Recommended Tire Pressure

Reply #9 –
Yahoo Message Number: 71898
Lee, I think you meant to say minus 60 degrees in Fargo ND. At that temp your numbers seem roughly correct.
Actually, I get 74 PSI for the proper tire temp in Fargo.

Jim

2005 Inspire #51225

From: "Lee Zaborowski"

Sent: Thursday, June 16, 2011 3:48 PM To: Country-Coach-Owners@yahoogroups.com Subject: Re: [Country-Coach-Owners] Re: Recommended Tire Pressure

Jim, there are so many variables, one PSI number does not apply to all circumstance. The only rule I worry about is not exceeding the max PSI for the rim at cool (69 F, 70 F, whatever . . .a toss up).
One guideline I believe in and many use is to determine your best PSI at 70 F, then add 10 PSI as a safety margin, as long as you don't exceed the maximum rim PSI. My ideal front PSI is 95, I run 105.My rims are good for 125 PSI.
For your comfort Jim, then if you go 10 PSI over the ideal at 70 F, you'd have to get down to 20F to get down to you recommend ideal PSI.

Lee

Re: Recommended Tire Pressure

Reply #10 –
Yahoo Message Number: 71899
Gees folks, the 68 was a typo.

Here is the drill -

70 F - 100 PSI
60 F - 98 PSI
50 F - 96 PSI
40 F - 94 PSI
30 F - 92 PSI
20 F - 90 PSI
10 F - 88 PSI
0 F - 86 PSI
-10 F - 84 PSI
-20 F - 82 PSI
-30 F - 80 PSI
-40 F - 78 PSI
-50 F - 76 PSI
-60 F - 74 PSI

So Jim you are correct. And yes, warm that tire at -60F back to +70F and indeed the pressure will again be 100 PSI.
Its the Ideal Gas Law (PV=nRT). More correctly the PSI change for 10 F change is closer to 1.8 PSI, but for our needs, 2 PSI is close enough.

Lee

Re: Recommended Tire Pressure

Reply #11 –
Yahoo Message Number: 71900
Lee, .just think how we could turn on you........ if we did'nt like you

AL

Re: Recommended Tire Pressure

Reply #12 –
Yahoo Message Number: 71902
Lee,

We have a misunderstanding here. The second paragraph, of my post, explains my belief about tire pressures. "Following this subject on several forms, it became more confusing to me so i sent an email to a tire manufacturer, Bridgestone if I recall correctly, asking them for clarification. There response was as I stated in my previous post. The tire/load charts from all the tire manufactures web sites do not specify temperatures except they should be cold. They do not define cold. That's why I asked Bridgestone for clarification." If your tire/load chart specifies 100#, then that is what it should be no matter atmospheric temperature providing the tires have not been driven on for several hours and are not subjected to the warming sun.
I'm not discussing about increasing the pressure above that specified in the tire/ load chart. Adding 5 or 10 pounds for safety reason is a personal decision and has nothing to do with manufacture recommendations. I don't know of any tire manufacturer that recommends a 5 or 10 pound increase over the tire/ load chart. You said many people use that as a "guideline". Where did this "guideline" originate? I'm not suggesting you should not do this, just pointing out it is not addressed by manufacturers.

Jim E

Re: Recommended Tire Pressure

Reply #14 –
Yahoo Message Number: 71907
Jim, I do not mean to be argumentative. If I came off that way I apologize.
The only thing I questioned was the assertion that one should change the 'at rest' tire pressure every time the air temperate changed. IMHO, that is flat out wrong.

Then there was my 68PSI-98PSI kerfuffle.
The Bridgestone information is accurate as far as it goes . . . inflate to the recommend pressure for the load. But, there is nothing wrong with a higher pressure as long as you do not exceed the rim and tire upper limitations. It it my understanding that this is a common trucker trick.
As to the 10 PSI safety margin, I suggest you go back to Post #2 in this thread by Ron Baran, which makes my case.

Lee

Re: Recommended Tire Pressure

Reply #15 –
Yahoo Message Number: 71912
I never once said to change the pressure with temperature changes. What I said was, the pressure should be what the load inflation tables indicate. Temperature is not a factor. Only that they should be "cold". "Cold" is defined as the temperature after the tire has been at rest for 3 or 4 hours and not warmed by the sun. That would be atmospheric temperature. Now, having said that, it stands to reason that if you start in Fargo, at 60 degrees, with 100 pounds and add 5 or 10 pounds as a safety factor, then arrive in Yuma, at 95 degrees, you will probably be over inflated.

I was not involved in the 68psi-98psi kerfulle.
I believe the Bridgestone information is 100% correct. Adding 5 or 10 pounds is a non issue. They do not recommend it nor disagree.
I went back to post #2 and found nothing that is contrary to what i have been saying from the beginning. There is no case involved. I have never said you shouldn't inflate 5 or 10 pounds over what the load inflation tables indicate. What I think is, over inflation affects ride quality all though I have never found this to be true. Therefore it is a non issue with me. I do in fact add a couple of "margin" pounds. I also check my tire pressure every day, when traveling, if the sun has not warmed them.

Jim E

Re: Recommended Tire Pressure

Reply #16 –
Yahoo Message Number: 71933
A few comments on this subject. People who first pose the question of what tire pressure to use are often new to RV's and/or heavy vehicles and apparently never really considered the subject before although what pressure to use applies to autos as well maybe less critical because of a less possible range of loads.

What is your object is in choosing a pressure? Are you going for maximum mileage? Best ride? Best handling? What type of road surface do you usually drive on? Speed? I'd guess most of us are interested in a reasonable compromise workable pressure that works Summer or Winter regardless of where we might be based.

Fine tuning is OK but all this talk about tire manufacturers' tables fails to note except in one post the qualification that applies to them:

"That's what I used to think. In fact, I had a chart, that I downloaded >>> from the internet, showing minimum pressures at different temperatures."

The key word here is "minimum".

Weighing your coach is good to encourage good distribution and avoiding being over weight limit specs. Beyond that don't exceed the placard limits which are probably based on max weights, rim and tire limits. Assuming your weights are within range I'd guess that for most choosing a pressure above the tire manufacturer's minimum for that weight and less than the coach placard which I think are generally maximums - but closer toward the coach placard than the tires manufacturer's minimums. If this gives you reasonable handling and ride for your usual surface without abnormal tire wear or wear patterns forget about all this fine tuning and use it. Just be sure your pressures are equal when initially checking while "cold" across each axle. If you have a TPMS (Tire Pressure Monitoring System) that works be aware of changes especially between axle mates.

Jim M

'02 Intrigue #11410 ISL 400

Re: Recommended Tire Pressure

Reply #17 –
Yahoo Message Number: 71940
These posts are always fun, and search usually will find all of the times it's been reviewed before (on many sites, not just ours - it's like oil, always good for a lot of dialog:)!)

My way:

-4 corner weight

-Mfg Chart for my tire

-Add 5 PSI for contigency and weather fluctuations -Check wear, tweak if needed (never needed so far) -Maintain

This in my vast experience (two RV's, two sets of tires:)!), is always way below the Max CYA of the Mfg Plate in the RV. It usually provides the best ride comfort, and control. I did go up another 5 PSI on the little Bounder's F53 chassis, as the the front weight was way below the minimum weight range on the chart. With the extra 5 PSI, they were still very soft (I think 70 PSI, on the 19" Goodyear G670's.) I bumped this to 75 PSI, good ride, good handling, wear was not a problem.
I think the key word in Jim's and others updates is 'think'. Stay within the safety guidelines, but 'think' things over for your application.

Go set them, maintain them where needed, and go have some fun...
Best to all,
Smitty

04 Allure 31017
04 Allure Sold to a nice new owner! Now enjoying a 07 Magna Rembrandt 45' ISX600 #6775
"We're ONDROAD for THEJRNY!" (Toad and Coach license plates, say Hi if you see us!)
 

Re: Recommended Tire Pressure

Reply #18 –
Yahoo Message Number: 71945
I found the last two posts from Jim M and Smitty refreshing and good comments to enhance tire care.
Personally, I tend to get wound up on this topic as I've observed that some folks: (1) do not understand very well the dynamics and effects of ambient temperature or heat build-up while driving, on pressure and :(2) the reversibility of pressure in that the tire will return to the original pressure when the tire is at the original temperature.

So, I get adamant about some concepts.
The negative outcome to a poor understanding of gas law dynamics is then, is as the temperature is different day by day, some folks are regularly adding or removing air.
Generally (assuming no leaks and you should constantly monitor for that), you might add air 1-2 times a year. That's it.

Lee
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Lee Zaborowski

07 Intrigue 12153, Cat C-13