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Old 10-04-2012, 04:41 AM   #29
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Tire temperatures

dzhf0g - and anyone else who is interested,

There is an old rule of thumb that comes from the days before infared thermometers. It has a lot of experience behind it - and some good science, too!

The inflation pressure build up is a good indicator of the operating temperature of the internals of the tire - from the ideal gas law.

if you are experiencing less than a 10% build up, then that is good. If you are getting 10% to 15%, that needs to be monitored and possibly addressed. Anything over 15% needs to be addressed by increasing the load carrying capacity of the tire - by going larger in tire size or by using more inflation pressure. (OK, you could also slow down!!)

That is not a guarrantee that a tire won't fail, but it is a good indicator if you are overstressing your tires.
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Old 10-04-2012, 07:24 AM   #30
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dzhf0g - and anyone else who is interested,

There is an old rule of thumb that comes from the days before infared thermometers. It has a lot of experience behind it - and some good science, too!

The inflation pressure build up is a good indicator of the operating temperature of the internals of the tire - from the ideal gas law.

if you are experiencing less than a 10% build up, then that is good. If you are getting 10% to 15%, that needs to be monitored and possibly addressed. Anything over 15% needs to be addressed by increasing the load carrying capacity of the tire - by going larger in tire size or by using more inflation pressure. (OK, you could also slow down!!)

That is not a guarrantee that a tire won't fail, but it is a good indicator if you are overstressing your tires.

I understand that, but I'm also looking for temp cross reference. Also, I'm not too sure that the old rule of thumb is too accurate in modern tires (auto). It is absolutely common and normal to see (using TPMS) a modern car or truck with a recommended inflation pressure of, say 30 psi, rise 4 psi during a highway drive in very moderate temps at 65 mph. No load, other than driver. So I think the 10 and 15% figures may be out dated. I have noted this on many cars and trucks I drive for my work. The rise is pretty consistent at 15% with just me in the vehicle....no load....at recommended door jamb pressures.
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Old 10-04-2012, 08:57 AM   #31
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I just finished a 3000 mile trip on my 4 year old GYM's, D-rated, that included about 30 miles of washboard dirt roads. Inflated to just under 60psi, I was getting readings just over 100 degrees with my IR thermometer, checking the sidewalls, each time I checked. A bit cooler than my TV. Sounds like I may drop to 55psi without concern. I'm happy.
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Old 10-04-2012, 10:47 AM   #32
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I just finished a 3000 mile trip on my 4 year old GYM's, D-rated, that included about 30 miles of washboard dirt roads. Inflated to just under 60psi, I was getting readings just over 100 degrees with my IR thermometer, checking the sidewalls, each time I checked. A bit cooler than my TV. Sounds like I may drop to 55psi without concern. I'm happy.
Robert, while there seems to be a lack of definitive information from tire manufacturers relative to tire temperatures, I don't think sidewall temps are the place to be making decisions. I believe you want to be taking readings between the tread blocks (or in the tread recesses, if you prefer) at the inside edge, outside edge, and center. IMO, most temp related failures, on street tires, result in belt separation, not sidewall failure. If those failures are temperature related and not a construction quality issue, I want to know the temps there.
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Old 10-04-2012, 11:55 AM   #33
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If someone is measuring tire temperatures to adjust inflation pressure, sidewall flex is what generates the heat that precedes blowouts. So, measuring the sidewalls would be justified.

However, I'm not sure running on underinflated tires to see if they heat up too much is the best way to determine the optimum tire pressure. It seems like you could possibly damage your tires before adding more air, which is kind of self-defeating.

It would seem more logical to weigh each wheel and then adjust pressure to the tire manufacturer's tire inflation charts. Or, just use the maximum sidewall pressure like Costco, Discount Tire and many others recommend for trailers.

As a side note, approximately 31% of all tires in the tire failure poll failed from blowouts, and 21% failed for tread separation.

FYI, we are still running the maximum pressure printed on the sidewalls of our Michelin XPS Ribs (225/75x16), which is 80 psi, with no apparent ill side-effects.
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Old 10-04-2012, 11:57 AM   #34
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I think that belt separation is found through a visual inspection as you check the temps. Monitoring sidewall temps to get a baseline, and then watching for any change, should indicate if anything is amiss. I'll check this weekend to see if there is any significant difference between tread, carcass, and sidewall temps.
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Old 10-04-2012, 12:39 PM   #35
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If someone is measuring tire temperatures to adjust inflation pressure, sidewall flex is what generates the heat that precedes blowouts. So, measuring the sidewalls would be justified.

However, I'm not sure running on underinflated tires to see if they heat up too much is the best way to determine the optimum tire pressure. It seems like you could possibly damage your tires before adding more air, which is kind of self-defeating.

It would seem more logical to weigh each wheel and then adjust pressure to the tire manufacturer's tire inflation charts. Or, just use the maximum sidewall pressure like Costco, Discount Tire and many others recommend for trailers.

As a side note, approximately 31% of all tires in the tire failure poll failed from blowouts, and 21% failed for tread separation.

FYI, we are still running the maximum pressure printed on the sidewalls of our Michelin XPS Ribs (225/75x16), which is 80 psi, with no apparent ill side-effects.
Good points, but I would not trust your poll figures. The average lay person cannot tell the cause of the blowout when they look at a shredded tire. I suspect that many of those blowout numbers were the result of belt/tread issues, not necessarily sidewall blowouts.

I think, and think only, that an elevated sidewall temp will be reflected in an even higher tread carcass temperature variation, due to squirm of the contact patch, in addition to high heat at the sidewall "bulge" at the very edge of the tread/sidewall interface. I don't believe sidewall temps any further toward the wheel tell you much, due to the wheel acting as a heat sink, and braking heat being applied to the wheel and transferred to the bead and sidewall.
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Old 10-04-2012, 12:41 PM   #36
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I think that belt separation is found through a visual inspection as you check the temps. Monitoring sidewall temps to get a baseline, and then watching for any change, should indicate if anything is amiss. I'll check this weekend to see if there is any significant difference between tread, carcass, and sidewall temps.
I will too. Leaving tomorrow.

I'll ask again. Has anyone found any credible expert websites with temperature discussions....except racing sites?
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Old 10-04-2012, 02:34 PM   #37
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Dznf0g, I'm not sure whether I can tell whether a tire failure is a blowout or tread separation, either (see photo of our GYM failure). However, does it really make any difference? It seems we are splitting hairs when a tire looks like this.




I am dumbfounded why some continue to try and justify running GYMs, when 55% of Airstreams reported tire failures with them. I am also puzzled why some insist on running less than sidewall maximum pressure when nearly all tire stores recommend it for trailer applications. The Airstream factory even recommends the maximum pressure printed on sidewalls.

I continue posting on tire threads hoping to help others avoid the inevitable GYM blowout/tread separation, and often-reported damage to their Airstreams. However, for many, this is a lost cause; and apparently, something that must be learned from personal experience.

Perhaps, I should just be satisfied that I have fixed my own tire worries, and let others figure this out for themselves.

For me, if a GYM run at any pressure ends up looking like the photo above, and Michelin XPS Ribs at 80 psi look like the photo below, I'll run the Michelins:



On a side note, while the Airstream Tire Failure Poll has faults, have you seen any other data on this or other sites that is similar? I have found only anecdotal accounts, which provide no numbers, whatsoever. And, the results in the Airstream Tire Failure Poll are sufficient for me to decide to never buy another GYM.
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Old 10-04-2012, 02:49 PM   #38
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Phoenix, nope......but that's not my position on any of the posts I have made here. My only comment was that when a tire looks like yours (sorry btw) it is very difficult to determine whether it was a sidewall blowout or a tread related blow out, therefore the poll responder kinda just picks one of the choices.

I run 16" LTs. I don't like any of the odds with any brand ST.

I'm just trying to find the best pressure for my particular load when there seems to be a total lack of definitive expert sources. (lots of opinions though!) You and I do disagree on the max sidewall pressure thing with a lesser load than associated with that sidewall marking.
That's been dragged around enough. I have my opinion and you have yours. That's not bad....just different.
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Old 10-05-2012, 07:25 AM   #39
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A couple of thoughts

First, is that trying to figure out the cause of a tire failure is difficult. It's especially difficult when the tire is damaged AFTER the failure takes place - like between the time the failure is noted and when the vehicle stops. Much of the evidence needed has gone missing. I know, because it is what I do for a living.

So I would expect that the average joe would have even more difficulty - and based on my experience, more often wrong than right.

An example is in another thread where someone reports sudden blowouts on trailer tires. Since the driver doesn't feel anything as a trailer tire deflates, how can one know? (and I hope people will not take offense. I am merely pointing out the difficulty about being certain of something one is not in a position to know directly.)

The second thought is about the "Airstream Tire Failure Poll". I am really interested, but can't seem to find it. Anyone got a link?
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Old 10-05-2012, 08:50 AM   #40
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http://www.airforums.com/forums/f438...oll-76867.html
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Old 10-05-2012, 11:53 AM   #41
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Thank you so much. Very interesting.
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Old 10-09-2012, 03:05 PM   #42
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Morgan Guy, check the Maxxis website. There you will find the load ratings at different air pressure. The idea that you should inflate to the maximum side wall psi listing is simply false. If you have E rated tires, you can inflate them to a D rating of 65 psi and have a good margin on your Airstream. An E rated tire inflated to 65 psi is a much stronger tire than a D rated tire inflated the same. You made a good choice and should inflate to reflect your load plus a safety margin.
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