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Old 04-09-2015, 08:18 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, 09:52 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, 10:00 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, 06:27 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, 07:50 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, 08:40 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, 06:34 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, 08:02 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, 08:31 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, 09:17 AM   #38
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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.
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, 09:31 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, 09:38 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 10F 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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Old 04-13-2015, 09:45 AM   #41
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I assume you meant your TT tires are LT225/75R16 LR-E. Are your TV tires LT275/65R18 LR-E ?
Yes, those are the sizes, but of course I have no way to measure the moisture content of the air in the tires, and it's just air, not pure nitrogen.

But after reading your next to last post, I will again state my concern....my hotter running tow vehicle tires have less pressure gain than my cooler running travel trailer tires. Seems contradictory to me, but as I read what you guys are saying, my IR temp gage is the culprit, and should not be believed?
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Old 04-14-2015, 06:10 AM   #42
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...But after reading your next to last post, I will again state my concern....my hotter running tow vehicle tires have less pressure gain than my cooler running travel trailer tires.......
Steve,

The problem here is that you think that a tire with a higher temperature IN ONE SPOT is hotter everywhere - and that is not true. There can be significant temperature differences around the tire and because they are caused by different things, they can be different between different tires even though they are operating in the same environment.

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..... Seems contradictory to me, but as I read what you guys are saying, my IR temp gage is the culprit, and should not be believed?
No, it is likely reading what the temperature is in that one spot - and the same spot on a different tire may be different.

Try this as an experiment. Take IR readings at the tread center, tread shoulder, mid-sidewall,, rim edge and wheel center. Do it for all 8 tires. Did you get the same values? Are they consistent?

Prediction: You already know the tread surfaces are different, but I'll bet that as you move down the tire, they will get closer, and the wheel centers will also be different.

Please note: you should do this as quickly as possible as soon as you come to a stop so everything doesn't have a chance to cool down. It might be good to have an assistant write while you call out the numbers.

Oh and let us know the results. It will be educational for many who visit this website.
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