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Old 04-05-2015, 03:15 PM   #21
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I have been told by tire "experts" if your hot tire pressure increases more than 10%, you started with too low pressure when the tires were cool.

However, we've all heard the definition of an "expert".
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Old 04-05-2015, 04:28 PM   #22
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Steve, I always heard the same thing, but my AS Michelins will gain 8-9 psi whether I run them at 65 psi or 80psi. No they are not overloaded either. About 1900 lbs per tire
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Old 04-05-2015, 04:33 PM   #23
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Originally Posted by Andy R View Post
I recently found this website (Polo.com Vinatage Airstream Page) for One-Of-A-Kind Ralph Lauren Airstreams. Each vintage Airstream trailer is offered at $150,000. Proceed to be donated to charity!

Adirondak Caravel - Sold for $150,000
Main Page - Features Page - More Pictures


Nautical Bambi - Sold for $150,000
Main Page - Features Page - More Pictures


Utility/Surplus Airstream - For Sale $150,000
Main Page - Features Page - More Pictures


Western Bambi - For Sale $150,000
Main Page - Features Page - More Pictures


I really like what they have done. I think these units are works of art! That a way to go Ralph Lauren!
Doug,
TPMS measured at the stem area will be considerably cooler than the shoulder area rubber. That is the hottest part of the tire that we can measure. A probe sticking into the rubber is the most accurate, but that is destructive.
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Old 04-05-2015, 04:59 PM   #24
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Not sure what in the world happened when I tried quoting Doug ' s text on my phone????
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Old 04-06-2015, 01:27 AM   #25
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If I remember right there was a thread here written by a guy who worked for one of the big tire firms and retired? I think he said when you get above 140°F you better be pulling into a dealership as it was getting ready to fail.

A friend who runs motorhomes was checking his temps with IR thermometer and checked the temps on a friend's rig with him. He told the friend one tire was getting ready to fail, owner kicked it and said it was OK and 75 miles down the road it came apart.

On new tires I check at 50 miles, 100 miles to get an idea of how things are progressing and all are within 3°. The tires I got from Tredit were made in Taiwan? I did 3400 miles trip on them. I can't tell any wear difference in any of them and they still have the bumps on them on the outer edges with I think 6000 on them now.

I also carry my own 120V compressor I got from sears with a wet sump pump and put Mobil 1 synthetic in it. It weighs about 40 lbs I guess and I have a 25 ft hose on it. Before I hit the road coming home I check pressures cold and adjust as needed.

I figure if they did not want 80 in them they wouldn't put 80 on them. That is what my TV calls for so I have 80 in everything cold.
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Old 04-06-2015, 07:48 AM   #26
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Originally Posted by dznf0g View Post
Doug,
TPMS measured at the stem area will be considerably cooler than the shoulder area rubber. That is the hottest part of the tire that we can measure. A probe sticking into the rubber is the most accurate, but that is destructive.
Thanks Rich - I will try to remember not to stick any probes into the sidewalls..... Your comment on the temp differential seems to make sense though. Thanks for your thoughts.
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Old 04-07-2015, 11:40 AM   #27
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Sounds like some inaccurate recollections and misunderstood information.

If Hummer is talking about me ( Retired Tire Engineer ) I doubt I ever said 140°F indicated immanent failure. Now maybe I answered a specific question and said something like 140° above ambient was way too high.

BUT this also raises the problem/question of what temperature you are talking about.
Tire surface temperature as read by an cheep IR hand gun or internal air temperature and measured by an internal TPMS or inflation pressure air in the valve stem measured by an external TPM or rubber temperature internal tot he tire structure when measured with a needle probe.

My internal TPM give me hotter temps than my external TPM by about 5 to 8°F. The TPMS give temp range of 10 to 15° hotter than ambient unless things like rain or wet road are involved.

No single simple answer.

The use of a probe MAY be destructive but not if you have been properly trained. This is how we get the most meaningful temperature on race tires but if you are not careful you can turn a $400 tire into scrap if you do it wrong.
I have a number of posts on both Temperature and Infrared on my blog with comparison test data if you are interested.
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Old 04-09-2015, 07:07 AM   #28
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Just like Roger, I want to emphasize that the internal temperature of a tire is the important value and you can NOT measure it. What IF thermometers read is the EXTERNAL temperature and that may have a lot to do with the road surface temp. It is not uncommon for road surfaces to reach 120°F. Then again, they could be well below freezing!

The most reliable way to get a handle of where you are is by pressure buildup. Anything less than 10% is good - and anything over 15% needs to be dealt with immediately. Please note: 10% is NOT a target!! It is an upper limit.

So those folks who have IF devices, try to correlate the pressure buildup to the reading you get from the tread surface. I'm sure it will be highly variable and weather related.
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Old 04-09-2015, 07:18 AM   #29
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CapriRacer,

Please explain something to me if you will. With my rig I get more than 10% pressure increase in my trailer tires, and less than 10% pressure built in my tow vehicle tires. Yet, with an IR thermometer my trailer tires (225/75X16E Michelin @ 70psi cold) run cooler than my TV tires (276/65R18 Michelin @ 70psi cold), by about 10 degrees.

Per scales, truck is 4600+,- front and rear, and trailer tires, 8500/6.

Why?
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Old 04-09-2015, 08:52 AM   #30
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CapriRacer,

Please explain something to me if you will. With my rig I get more than 10% pressure increase in my trailer tires, and less than 10% pressure built in my tow vehicle tires. Yet, with an IR thermometer my trailer tires (225/75X16E Michelin @ 70psi cold) run cooler than my TV tires (276/65R18 Michelin @ 70psi cold), by about 10 degrees.

Per scales, truck is 4600+,- front and rear, and trailer tires, 8500/6.

Why?
VERY GOOD QUESTION!, Steve. I have noted the same thing....or at least similar.
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Old 04-09-2015, 09:00 AM   #31
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When I picked up my first trailer back in 2007, a 19' Bambi, the original owner told me he had been running the GYM's at 50psi (for 3 years) for a softer ride. On the way home, I filled them to 65psi and went on my way.

A few months later while traveling the interstate fully loaded, one of the tires started to deflate. It hat busted the seal loose at the rim and started losing air. The dealer who replaced said the sidewalls had become soft and unable to support the weight because they had been run a too low of pressure and were over flexed.

So my advice is to run your tires at or near their intended pressure unless you want to risk having your tires fail.
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Old 04-12-2015, 05:27 AM   #32
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CapriRacer,

Please explain something to me if you will. With my rig I get more than 10% pressure increase in my trailer tires, and less than 10% pressure built in my tow vehicle tires. Yet, with an IR thermometer my trailer tires (225/75X16E Michelin @ 70psi cold) run cooler than my TV tires (276/65R18 Michelin @ 70psi cold), by about 10 degrees.

Per scales, truck is 4600+,- front and rear, and trailer tires, 8500/6.

Why?
As I have said before, I think you will find that the correlation between IR readings at the tread surface and the pressure buildup are NOT very good. The temperature of the tread surface is highly dependent on the surface temperature of the road. With the tow vehicle having a wider tread than the trailer tires, it will pickup more road surface temperature.
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Old 04-12-2015, 06:50 AM   #33
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I agree with Capri. I have never been able to make any definitive analyses with the IF relative to pressure rise and casing temp. The IR is good for noting any significant deviation among the four tires which may require attention, but that's about it. And you still have to account for sun exposure.

But back to Steve's question: Why do we see a greater AS tire pressure rise when compared to TV? I mind the 85% rule and run at 80psi (last year), have 1900# on the tires (give or take). The truck has more weight, runs at a lower pressure (per placard), is an LT. Truck gains 4 - 6psi. Trailer 7 - 9psi.

Is it airflow???????
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Old 04-12-2015, 07:40 AM   #34
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Originally Posted by CapriRacer View Post
As I have said before, I think you will find that the correlation between IR readings at the tread surface and the pressure buildup are NOT very good. The temperature of the tread surface is highly dependent on the surface temperature of the road. With the tow vehicle having a wider tread than the trailer tires, it will pickup more road surface temperature.
Not saying you're wrong, but not sure I accept this, and here's my reasoning.....Yes the truck tires are wider, but they run on the same temperature surface, and because they are wider, they also have more area to dissipate the heat.

Now if you had said the truck tires are doing more work, as in absorbing the torque from the power train, and steering the rig down the road????, I'd buy that. However, that explains only the higher temps in the truck tires, but provides no explanation for the larger pressure rise in the trailer tires.
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Old 04-13-2015, 05:34 AM   #35
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Not saying you're wrong, but not sure I accept this, and here's my reasoning.....Yes the truck tires are wider, but they run on the same temperature surface, and because they are wider, they also have more area to dissipate the heat.

Now if you had said the truck tires are doing more work, as in absorbing the torque from the power train, and steering the rig down the road????, I'd buy that. However, that explains only the higher temps in the truck tires, but provides no explanation for the larger pressure rise in the trailer tires.

If we start with the idea that the pressure buildups are different to begin with, then all we are looking for is an explanation for the reversal in tread surface temp.
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Old 04-13-2015, 07:02 AM   #36
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If we start with the idea that the pressure buildups are different to begin with, then all we are looking for is an explanation for the reversal in tread surface temp.
Is not "pressure buildup" a result of heat?

That's basically my point of not understanding. Why does a tire that gets hotter, not gain as much pressure, and vise versa.

You continue to make statements like the one above that goes on assumptions that I have not seen proven, and make no logical sense. Why would we assume "that the pressure buildups are different to begin with"?
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Old 04-13-2015, 07:31 AM   #37
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Steve, I'll throw this out as a possibility only...cause I don't know.

I can only deduce that the higher pressure buildup is a function of the airflow in and around the wheel well.

As Capri, has said, tread temp isn't a great indicator of the air volume actual temp inside the tire. My understanding is that the wheel is the greatest heat sink for the air to transfer heat. My suspicion that there just isn't as much airflow around the AS wheels as the truck. It's "dirtier" air that is blocked by the truck and ASes are low to the ground with less airflow under the trailer.

Just a theory, since I can conceive of no other.
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Old 04-13-2015, 08:17 AM   #38
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As I have said before, I think you will find that the correlation between IR readings at the tread surface and the pressure buildup are NOT very good. The temperature of the tread surface is highly dependent on the surface temperature of the road. With the tow vehicle having a wider tread than the trailer tires, it will pickup more road surface temperature.
As the other tire engineer on RV forums I agree with Capri. I have run direct comparison test of IR vs internal TPM va External TPM vs Race tire needle temperature probe. IR is least reliable followed by external TPM then internal TPM
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Old 04-13-2015, 08:31 AM   #39
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RE question on temperature increase.

Many seem to think the primary source of heat energy is from transfer from road surface to the tire. In fact the primary source of heat as measured in the laboratory is heat generated at the belt edges due to the rubber flexing. This heat then conducts though the rubber (a poor conductor by the way) to both the inner air chamber and outer tire surface.
The contained air is warmed from the hotter tire shoulder area and heat is taken away by the wheel and relatively cooler sidewall. BUT the metal wheel is a much better conductor of heat so most of the heat is transferred out through the wheel to the outside air.

Not the heat that goes out from the belt area gets to the surface where it either transferes to outside air in the base of the slots and grooves or must continue through the solid rubber (insulator) of the tread and shoulder blocks & ribs.

As you can see this is a very complex heat generation and flow situation.

One thing that has not been accounted for is the heat generation properties of the different rubber compounds.

TV tires have been designed with cooler running compounds to help deliver better MPG. This is expensive. TT have a primary goal of being low cost so the compounds used have not been optimized for low heat generation.

It is also probably true that for a given size the TT tires have higher load which means more deflection which means more heat.

To do a valid comparison one would need identical tires under identical loading on both TV & TT filled with air (% moisture) from the same compressor.
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Old 04-13-2015, 08:38 AM   #40
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CapriRacer,

Please explain something to me if you will. With my rig I get more than 10% pressure increase in my trailer tires, and less than 10% pressure built in my tow vehicle tires. Yet, with an IR thermometer my trailer tires (225/75X16E Michelin @ 70psi cold) run cooler than my TV tires (276/65R18 Michelin @ 70psi cold), by about 10 degrees.

Per scales, truck is 4600+,- front and rear, and trailer tires, 8500/6.

Why?
Pressure increased by about 2% for each increase of 10°F NUT this is based on dry gas. Are you sure the moisture content in all tires is the same?

It would also help to know the actual tire size and design. I assume you meant your TT tires are LT225/75R16 LR-E. Are your TV tires LT275/65R18 LR-E ?
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