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Old 10-25-2020, 07:01 PM   #43
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Originally Posted by RVPioneer View Post
The guy at NAPA must be related to the guy at Pro Tire.

Tire pressure gauges measure the air pressure above atmospheric pressure. At sea level that is 14.7psi, at 7000’ it is 11.3psi. Worst case, it’s off by 3.4psi.



Why do I find many gauges reading 5 to 10 psi wrong when compared to a certified gauge?
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Old 10-25-2020, 07:08 PM   #44
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Correct "RV Tire Pressure" is not rocket science. See post # 36.
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Old 10-25-2020, 07:13 PM   #45
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Originally Posted by TurboDaveTX View Post
snip


I have found that the pressure difference from gauge to gauge to be 10 to 15 pounds different.snip Agree

NAPA guy said that the digital gauges are calibrated at sea level so it is likely they would read 10-15 lbs low if you are at 7,000 or more ft. Do not agree


There have been many front tire failures on Anthems and may be in part the result of over inflation. Definitely do not agree

snip


Not sure what the answer is to where or how to find an accurate tire gauge, but my advice is not to rely on a digital gauge and get the best gauge you can find and have a TPMS installed. The NAPA traditional truck gauge seems to be closest to the reading on the TPMS. I use the TPMS to verify tire pressure with the gauge.

Why do you think your TPMS are accurate. In my TPM comparison test I found the numbers were off by a few psi
This data compares the two TPMS with my accurate hand gauge with the tires all set to 65.0 psi cold









Another comparison of some different sensors gave
The target pressure is 80.0 psi as reported by my handheld digital gauge.

Set A 1 reading of 78 psi, 5 readings of 79 psi
Set B 2 readings of 78, 2 readings of 79 and 2 readings of 80 psi

I also recorded the temperature.
Set A 4 readings of 66 F, one each of 64 and 68F
Set B 4 readings of 69 F and 2 readings of 68


I have covered this issue in detail in my blog. (sorry not allowed to tell you the link)
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Old 10-25-2020, 07:15 PM   #46
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Originally Posted by Johnontheroad View Post
I hardly ever have to adjust tire pressure, but when I do, I try to do it in the morning when temps are near 68F. And then I inflate to tire mfg rated specs based on measured tire load. Once set I forget about it, except keeping an eye for anomalies on my TPMS system.

So if it’s cold one morning and my tire pressure is below what I normally set it at I just ignore the delta difference. Once on the road the tire quickly heats up to the normal running pressure.



This is not the correct way to set and run pressure. You should NEVER depend on the road heating to get to your goal pressure. If you are doing that you are intentionally running underinflated. Not good.
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Old 10-25-2020, 07:16 PM   #47
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Originally Posted by brobox View Post
When I four corner weighed at NIRVC the Michelin chart showed my pressure 110 front 80 drive 90 tag loaded for travel. However the Valid TPMS monitor does not work in FL heat with the correct tire pressure



Get a different TPMS.
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Old 10-25-2020, 07:18 PM   #48
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Originally Posted by arnold931 View Post
This article is from TechnoRV. The author says Ambient Temp IS 70 degrees.
https://www.technorv.com/articles/am...tire-pressure/



Incorrect. I will notify him as such,
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Old 10-25-2020, 07:25 PM   #49
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Quote:
Originally Posted by RM Art View Post
Correct "RV Tire Pressure" is not rocket science. See post # 36.
If that were true, then manufacturers would not bother to print inflation tables. The pressure on the sidewall is the "Not to exceed" pressure when the tire is at ambient temperature.
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Old 10-25-2020, 07:34 PM   #50
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Originally Posted by Tireman9 View Post
Why do I find many gauges reading 5 to 10 psi wrong when compared to a certified gauge?
Not sure your question is relevant to my statement. But you’re the tire expert, so you should know why tire gauges give different readings.

My point was to show the difference one would see in tire pressure between sea level and 7000’. You should know that as well.
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Old 10-25-2020, 11:14 PM   #51
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Originally Posted by Tireman9 View Post
Paying more for a gauge does NOT mean it is more accurate. I have three $10 digital gauges that read to +/- 0.5 psi and all three match (+/- 0.5 psi) a ISO certified laboratory master gauge used in a tire test lab in Akron.
You can Learn more here. You will still need a dual foot gauge if you don't run extension hoses on your rear duals but this can be a good "Master Gauge.


NOTE I get no comission on this gauge. I bought mine and know they work better than most other gauges.
I've got the same digital gauge. They claim +/- 1 psi accuracy. I've got a new Milton truck gauge, dual foot. I checked both of them at a Michelin dealer's in Twin Falls a few months ago. 100 psi certified gauge checker it claimed. Milton read 92, Accutire read 98. The Accutire is now my standard to "calibrate" the rest of my gauges.
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Old 10-26-2020, 03:38 AM   #52
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Originally Posted by garysfb View Post
While there have been many threads about tires and tire pressures, I don't recall this point being discussed:

I was at NIRVC today to have new Michelins put on the front as well as an alignment, part of the repairs from my earlier blowout. Pro Tire did the work. I started talking to the tech about pressures as they relate to changing temperatures, especially driving north from Mississippi, or Texas for that matter, it was over 100 yesterday!!!

At any rate he said that according to Michelin the optimum ambient temp to set pressures was 70 degrees give or take 5, and you are good to go no matter the temp changes. I had thought that they should be set according to the AM temp, before the sun hits them, for whatever the temp is where you are.

As an example if I set them at home at 70 degrees and travel north where it's 50 degrees in the morning and pressures are down 5 lbs., I should add 5 lbs. NOT SO HE SAID. If you set them at 70 +/- 5 degrees you are good no matter how much colder it gets. This leaves me concerned about under inflated tires when driving up north. Especially since I'm traveling up to Charlotte, Michigan to have the chassis inspected before our 3 year warranty is up.

Can anybody shed any light on this?
I think I can shine a light on it.

Pressure advice is to prefent the tire from overheating, when driving the speed constantly , for wich the pressure is determined.
No part of rubber of tire may come above a critical temperature at wich the rubber hardens and beginning cracks are made. Those cracks tear further in time by mechanical forces, untill mayby only after 3 years that far that treath separates or tire blows. Then that once the conditions at wich tire overheated, is long forgotten.

The temperature of rubber is made by the balance between heating up and cooling down.

Cooling down is dependent on temperature, differences between rubber and in and outside tire gascompound.

Heating up by driving only, is dependend on heatproduction a cycle bij the bending of the rubber by deflecting and flexing back every cycle.
But also on the number of cycles a second the tire makes.

If you determine pressure for a certain speed and load on tire, it is for 65 degrF, some say 68, but 70 degrF also is that close that it wont give such difference in pressure, that it will be a problem.

When colder outside, the cold pressure( when temp in and outside the tire is the same) goes lower, wich gives more deflection of the tire, so more heatproduction a cicle, so a second at same speed.
But also the temperature/differences are larger between critical temp of rubber, and in and outside tire's air( or other gascompound), so cooling down is also better.
Within a certain range of outside temperature, the heating up and cooling down stays in balance, so rubber still wont overheat.
So for savety, you dont have to highen up the pressure to calculated advice. For fuelsaving and roadhandling you may do so.

When hot outside, the other way around, higher cold pressure, so lesser deflection, so heatproduction a second, but also lesser tempdifferences between critical rubbertemp and in and outside air, so lesser cooling down a second. Then you need the higher pressure , and never blead down to advice .
You may notice different roadhandling bya harder ride though, but savety first.

So the person at the tireshop was right to the conclusions this " pigheaded Dutch selfdeclared tirepressure-specialist" , so not a professional.

Once you determined the needed pressure with reserve, based on best,weighed axle-end loads in the loading you go on trip, second best Axle-loads, I can calculate a safe highest pressure with still acceptable comfort and gripp for you.

Then this is for 65 degr F outside temperature, cold measured.
I then can make a pressure/ temperature-list for those pressures, so you can look back, what the cold pressure should measure on a hot or cold day, but also, if you have tmps with external sensors, see what the inside tire temp is, because those sensors dont give the temp in tire, but something in between in and outside tire, so lower then real, so unreliable.

These lists then are a better indication then what your tmps gives, but still an indication, because you never can measure the pressure that accurate, and in my list , I assume no vollume-chanche when pressure chanches, wich it will practically be for a already pressurised tire.
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Old 10-26-2020, 05:01 AM   #53
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Originally Posted by Tireman9 View Post
Get a different TPMS.

I would LOVE to, it is a factory installed Valor, in dash system installed by Spartan built into the Valid digital dash. It is a POS. Internal sensors instead of SIMPLE screw on exterior sensors. And they do not have a temperature default range to work on really hot pavement. The are designed to work in the the text book range 74 degrees, not TX FL or NV. Did I mention it is a POS.
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Old 10-26-2020, 09:23 AM   #54
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If that were true, then manufacturers would not bother to print inflation tables. The pressure on the sidewall is the "Not to exceed" pressure when the tire is at ambient temperature.



Not quite. The Max Load number on the tire sidewall is just that. The maximum you should ever place on a tire. The pressure associated with that Max load is actually the MINIMUM pressure needed to support that stated max load.


If you run lower pressure then the load capacity is decreased.
Look at the charts and this will become clear.
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Old 10-26-2020, 09:25 AM   #55
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I would LOVE to, it is a factory installed Valor, in dash system installed by Spartan built into the Valid digital dash. It is a POS. Internal sensors instead of SIMPLE screw on exterior sensors. And they do not have a temperature default range to work on really hot pavement. The are designed to work in the the text book range 74 degrees, not TX FL or NV. Did I mention it is a POS.



What does Spartan say when you point out that their "Safety" device doesn't work at higher operating temperatures?
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Old 10-26-2020, 09:39 AM   #56
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Originally Posted by RVPioneer View Post
Not sure your question is relevant to my statement. But you’re the tire expert, so you should know why tire gauges give different readings.

My point was to show the difference one would see in tire pressure between sea level and 7000’. You should know that as well.



Not all gauges are accurate because they are a manufactured item which means there are variations in components. Different companies select different components.
Dial gauges can vary in their readings but better quality ones have an adjustment screw to allow calibration adjustment. No adjustment capability allowed the company to make a less expensive gauge.


Stick gauges are subject to wear and dirt than can affect their accuracy. Never seen a "stick" gauge that could be adjusted.


Digital gauges seem to be the most accurate. Not sure if they can be adjusted but my three Accutire gauges have have all tested within +/- 0.5 psi at 80.0 psi test level for the last 10 years. I did need to change the battery in one last year.
I figure the chance of all 3 going bad the same amount and the same direction at the same time is extremely small so I can do a self check by simply comparing the readings of the 3 gauges on my regulated fixture.
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