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Old 07-25-2010, 11:02 PM   #29
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Now, add the http://www.carlisletire.com/product_...are_safety.pdf
into this discussion. Page 2 says to always inflate ST tires to sidewall maximum or warranty is voided.
What about long-haul trucks? Does anyone reasonably think they change air pressure settings (based on altitude) after each mandatory rest break?
During the past month I have driven from 700' above sea level to over 9,000' without changing tire pressure. The 5er tires started with 80psi and right now, at West Yellowstone read 79psi (TPMS). It will be interesting to see the readings when we return to 700'.
IMO everyone is over-thinking tire pressure. REMEMBER_ all tire pressure charts reflect the minimum acceptable tire pressure for the corresponding load!
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Old 07-26-2010, 08:39 AM   #30
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Quote:
Also, a 4% or 5% change in pressure at 35# is not the same as that percentage change at 100#.
Thus the +5 psi idea- it is enough to cover most altitude and temperature variations.

Tire manufacturers know that temperatures vary dramatically in different climates, and at different times of the day. A 30-35 degree swing is typical from early morning to late afternoon, and then there is winter vs summer to consider as well. One has to assume that these dramatic differences are accommodated in the pressure recommendations in the charts. But then, we all know that assumptions can be dangerous!
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Old 07-26-2010, 02:05 PM   #31
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Originally Posted by Flagelpater View Post
Tireman9 Do you care to elaborate on my Over-inflation question? Also, again, Thank You for your very informative reply. This Forum is Great!
Over inflation has a number of negatives. Some more pronounced than others depending on how much overinflated you are as well as various vehicle factors but they include:
Hard Ride
Faster center tread wear
Increased chance of Impact (such as pot hole) damage, up to and including rapid air loss.
Faster degradation of suspension components
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Old 07-26-2010, 03:00 PM   #32
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I really don’t want to be argumentative but I firmly believe that the chart is incorrect in recommending that you overinflate your tires when the ambient is over 65F. You have provided a chart with no source or other information to act as a backup for it being valid. Asking for a reference to prove the negative (which is impossible), that 65 F is not what is meant by “cold” by the tire companies.
In my earlier post (7-24-2010 12:02 PM) I provided a direct quote from The Tire & Rim Association.
"The inflation pressure taken with the tire at prevailing atmospheric temperatures and do not include any inflation build-up due to vehicle operation."
Others have provided a quote from NHTSA
NHTSA uses the loads & inflations as published in T&RA for the test conditions that tires are required to pass before they can be sold for highway use in the US.
You seem to think that NHTSA regs do not apply to other than passenger but they cover all tires that are sold for use on public highways so RV tires are included.
If T&RA isn’t enough here is the definition from JATMA “Inflation Pressure: The pressure taken with the tyre at the prevailing atmospheric temperature, not including any inflation pressure build-up due to tyre usage”
Seems pretty clear to me that the current atmospheric temperature is the "cold" temperature used by the 25+ tire manufactures that subscribe to the published industry standards for load & inflation.

I want to make it clear that the numbers in your chart probably do represent the change in inflation you might see as you heat up a tire but that is not the same thing as setting your tire pressure to a higher pressure than the "cold" inflation because the ambient is hotter than 65 F.

Are you saying that your calculations are correct and the tire companies of the world are all wrong?

If my tires needed its Max inflation for the load and I happened to be in Phoenix one morning when it is 110 degrees you would have me increase my inflation pressure to 20 psi above the max stamped on the tire. Is this what you are advocating?

I certainly am not willing to make such a recommendation and I have 40 years of tire design and a couple of patents under my belt.

Personally I would not accept something published somewhere without proper source citation. Just because someone did the math for pressure change due to temperature does not mean they are correct in telling you that you need to ignore recognized, published industry standards.

Your chart says "The general rule of thumb is to inflate a tire to a proportionately higher starting value when the ambient tire/temperature is hotter than 65 degrees and to the recommended Cold Inflation Pressure value at temperatures below 65 degrees F."

Can you find this information that supports the idea that prevailing atmospheric temperature is 65F on any web site or document published by Michelin, Bridgestone, Goodyear, Toyo, Firestone, Maxxis, Yokohama, General, Perelli, or a site like Tire Rack or any car manufacturer site?
Jim
If you haven’t guessed, Tire inflation is a hot button for me.
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Old 07-26-2010, 03:09 PM   #33
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WOW, this thread is overwhelming. And I have taught a tire safety seminar and I thought I knew a bit about tire pressures. Much of my tire information came from two Michelin engineers when I sat at a table with them and we spread charts and tables all over a big table. We sipped coffee and had a long talk that continued the next day.

It was those two engineers who told me to add 5 psi to the chart and I believed them. My present motorhome was weighed by wheel position three times the first year I owned it and I have weighed it at least once a year since then.

The Michelin chart shows I should have 105 psi in the front tires for my weights. So I like to run 110 psi. A couple of months ago I left the south with 110 psi in the tires according to both my expensive tire pressure gauge and my tire monitor system. I have worked my way to Michigan with 9 overnight stops. Each morning before hitting the road I check the pressures and it has varied from 107 psi to 111 psi depending on the temperature and elevation. Since the chart says I should have 105 psi I have been safe to hit the road every morning. If I had left the south with 105 psi I would have to add or release some psi every morning.

By adding 5 psi I probably won't need to touch the tire pressures when I leave Michigan in October when it is much colder. I had much rather run +5 psi than -5 psi and be unsafe.
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Old 07-26-2010, 05:49 PM   #34
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Tireman9,

Quotes.

"If my tires needed its Max inflation for the load and I happened to be in Phoenix one morning when it is 110 degrees you would have me increase my inflation pressure to 20 psi above the max stamped on the tire. Is this what you are advocating?"

Where did I make such a statement? In this example, if you set your tire pressure in Fargo ND @ 65F they would be over inflated in Phoenix at 110F.

"You seem to think that NHTSA regs do not apply to other than passenger but they cover all tires that are sold for use on public highways so RV tires are included."

Where did I say that?

"The inflation pressure taken with the tire at prevailing atmospheric temperatures and do not include any inflation build-up due to vehicle operation."

Did you leave something out of this sentence? Is it taken out of context. The sentence is incomplete or something.

"Personally I would not accept something published somewhere without proper source citation. Just because someone did the math for pressure change due to temperature does not mean they are correct in telling you that you need to ignore recognized, published industry standards."

I have not seen anything that disagrees with this chart except your statements.

"The inflation pressure taken with the tire at prevailing atmospheric temperatures and do not include any inflation build-up due to vehicle operation."

I agree. The chart does not contradict this. Pressure build-up due to atmospheric temperature increases is not "vehicle operation".

"Can you find this information that supports the idea that prevailing atmospheric temperature is 65F on any web site or document published by Michelin, Bridgestone, Goodyear, Toyo, Firestone, Maxxis, Yokohama, General, Perelli, or a site like Tire Rack or any car manufacturer site?"

I assume you mean "cold" not "prevailing atmospheric temperature" is 65F. I can't find anything from any manufacturer that defines cold except as I have stated before, "first thing in the morning", "not driven for several hours", etc.

On several occasions you refer to "prevailing atmospheric temperature is 65F". To me, prevailing atmospheric temperature is whatever the temperature is at that moment in time.

By the way, you did not address my hypothetical situation of tire pressures in Yuma and Fargo.



Jim
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Old 07-27-2010, 01:50 PM   #35
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I have invited Pairajays to join me in PM as we try to resolve our differences off this thred as I think we are just confusing others.
Hopefully we can clear up our different interpritations. if we do, we will report back here.
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Old 07-27-2010, 02:35 PM   #36
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Sounds like a good plan Tireman9, but it's been interesting and informative. Seems there's just never a black and white "easy" answer to many of these technical things.

Good job keeping the disagreement on topic though.

Thanks to both of you for your insights.
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Old 07-27-2010, 02:46 PM   #37
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Tireman9 I will echo Ricko's comments. I do enjoy the technical stuff, although, I too do not want to overcomplicate any task. Reading the discourse turns ON a lot of lights for me. Please don't leave me in the dark!
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