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Old 04-21-2012, 07:30 AM   #15
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My trailer is 3500lb on a single axle. On the highway the pressures increase 6lbs. When bouncing down back roads the pressures will go up 2lbs. I assume the sidewall flex and friction is the cause of the increase.
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Old 04-21-2012, 09:46 AM   #16
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Until recently I owned a class-B, built on a Chevy 3500 chassis. When towing, it was not unusual for tire pressures to increase 15% or so (above 80 psi cold), before they'd stabilize. Going too fast on a hot day, they'd approach 20% over, and I'd have to back off to silence that annoying alarm.
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Old 04-21-2012, 10:19 AM   #17
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Not really. Regular air is about 80% nitrogen already. Plus, nitrogen and oxygen both expand/contract similarly with changes in temperature. Boyle's Law is the same for all gases or mixtures of gases.

The benefits of using pure nitrogen really are limited to longer tire life because the rubber inside the tire doesn't oxidize. However, since the rubber on the outside of the tire continues to oxidize, it's not much help there, either. Save your money and use regular air.
Yep...just a way for some of the BB tire stores to get paid for the free mount/balance you just got on your new tires.

Dryness is the only real benefit, I do use a dryer on our home compressor.

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Old 04-21-2012, 11:54 AM   #18
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[QUOTE=barts;1136529]For those that don't remember high school physics:
n = #moles/QUOTE]

Bart, I have trouble remembering high school. Moles? Won't they die if someone puts pure nitrogen in the tires?

Thanks for the tableógives me a good idea of how much pressure increase to expect. Is that tire temp or air temp? I guess tire temp because you have to go to Venus to get temps like 170˚ómore like 400˚ there.

I notice that after sunriseóan hour or so, the tires on the sunny side increase in pressure 2-3 psi if the covers are off.

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Old 04-21-2012, 12:52 PM   #19
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It's not just good sense, it's the law. Boyle's Law in this instance.
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Old 04-21-2012, 01:35 PM   #20
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Some reasons that (dry) nitrogen works well in tires are:

Nitrogen leaks through rubber less quickly than oxygen, apparently, so tires inflated with pure nitrogen will lose pressure more slowly than those filled with air. That said, I'd guess this is mostly not an issue for us trailering types, as we're careful about tire pressures already.

Water vapor will increase in pressure more quickly than dry air or nitrogen.n Unless special air driers are installed, the usual compressor/tank setup will deliver air saturated with water vapor; having dry gas inside helps reduce the pressure swings.

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Old 04-21-2012, 01:36 PM   #21
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Stan, if your cold tire pressure is measured at 50F, then the tire temperature that corresponds to 77 psi is 130F.

I have a single axle with about 2400lbs per tire, and I usually see a 10 psi increase from cold morning to 65 MPH in the afternoon. I think your pressure increase is a little higher than I would like to see. I'd check to see if you have a tight bearing or a draggy brake.
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Old 04-21-2012, 02:37 PM   #22
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Tire temperature

Barts, I think that you said keep the tire temperature below 160 - 170 degrees.
Maybe I should get a temp meter to go with the pressure gage.
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Old 04-22-2012, 01:14 AM   #23
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One of the those $20 infrared gizmos comes in hand for evaluating tire & hub temps.

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Old 05-20-2012, 02:59 PM   #24
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my tire gauge reads 50 psi on maxis M8008 radial (steel belted) ST225/75R15. 25ft AS Excella. Tire decal says max PSI inflation 80PSI. Person I bought TT from says 60 PSI inflation. HELP. Live in NC summer heat Eldin 89 AS Excella 25 ft.
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Old 05-20-2012, 03:42 PM   #25
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I have pressure and temperature sensors in my truck and trailer tires. The sensors are mounted on giant hose clamps on the inside rims, so you do not see them from the outside. The temperature varies greatly, and affects the pressure. The pressure that you mentioned sounds a bit high. I can get into the mid 70s on the rear tires of my 2500HD when I tow my 31ft. When my trailer tires reach 73 or so I start to worry, unless all four are showing the same thing.

Typically, I see a tire temperature of 35F above ambient. On a hot day this can definitely climb up there. Is the pavement new? Really black pavement is hotter than concrete, for example. The sunny side of the trailer is often up by 10 degrees. When it rains, it can bring down the tire temperature 20-30 degrees in a matter of a few miles. Speed brings up the temperature, of course. I often stay around 65MPH.

Temperature is often a better leading indicator of a problem than pressure. If one tire has a higher temperature than the others it is typically a sign of a mechanical problem, such as bearings, brakes dragging or a structural problem with a tire that is a few hundred miles away from popping.
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Old 05-20-2012, 04:03 PM   #26
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Quote:
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my tire gauge reads 50 psi on maxis M8008 radial (steel belted) ST225/75R15. 25ft AS Excella. Tire decal says max PSI inflation 80PSI. Person I bought TT from says 60 PSI inflation. HELP. Live in NC summer heat Eldin 89 AS Excella 25 ft.
Simple answer, go with what the trailer's owner's manual says for tire pressure. If you don't have and can't get the manual, then you can take the previous owner's word for it.

As long as that number is lower than the maximum pressure listed on the tires, anyway. Never exceed the pressure listed on the tires.
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Old 05-20-2012, 05:56 PM   #27
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Hotter tire "close to popping" - maybe not.

Quote:
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If one tire has a higher temperature than the others it is typically a sign of a mechanical problem, such as bearings, brakes dragging or a structural problem with a tire that is a few hundred miles away from popping.
Well, maybe, sometimes. I monitor my tire and hub temps at EVERY stop. The right rear tire on my tow vehicle ('08 GMC 2500/Duramax/Allison) always runs about ten to twelve degrees higher than any other tire on the truck. It has done that since the truck was new. Has done so for 60,000+ miles. Tire rotation doesn't solve it. Meticulous tire pressure checking (plus the TPMS readout) tell me it's not cold pressure related. And (I check, as mentioned), it's not hub / bearing temperature, either. And though I haven't scaled the truck and trailer from side to side, I load pretty carefully, so that the loads are very similar left to right. It's also not brake drag - the pads look identical left to right, and if they were dragging, I'd get hub temperature increase. First time I discovered it, I thought it was sun side / shade side differences. Not so.

Only thing I can think of is that since due to road crown, this is the "low" side of the truck, there is some weight transfer to that side, and since the rear tires carry more of the load, the right rear gets most of the low side "extra loading" and so more hysteresis effects from sidewall flex, etc. - outside of that, it's a mystery.

But it's not a tire with a structural problem that's about to pop.

BTW, the day I bought the truck, the salesman told me he'd seen a lot of them with this OEM tire (Bridgestone Duravis), and that "I'd really like them." ... of course, I thought that was a bunch of salesman malarkey, but at least insofar as durability is concerned, he wasn't fooling. I measured my tread depth earlier this week, and at 60,xxx miles, they still have half of their tread depth remaining ... and have always seemed to have reasonable wet and dry traction and also do o.k. in deep snow.
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Old 05-20-2012, 05:56 PM   #28
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The problem is that the owners manual was written for the original tires and the tires on the trailer could be a different rating.
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