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Old 05-20-2015, 01:52 PM   #29
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Just my opinion: Airstream, Discount Tire, Costco and others recommend "maximum sidewall pressure" for trailer tires. For load range E tires, that's 80 psi.

I have ridden in our 2005 19' Bambi at highway speeds, with OEM GYMs inflated to 65 psi and Michelin XPS Ribs inflated to 80 psi; and I could tell no discernable difference in ride.

Our tires have been inflated to maximum sidewall pressure for 10 years -- no calculations necessary...
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Old 05-20-2015, 01:59 PM   #30
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Yes, that's the confusion I'm getting here, if I set mine to 80psi cold, then get 10% I'm now over max. But if I set to 73psi + 10% that'd be 80psi.
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Old 05-20-2015, 02:09 PM   #31
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Tire Pressures and Tire Temperature

Keep in mind however, that tires filled to max cold sidewall pressures are engineered to handle higher pressures generated by road use. So for all intents that max pressure rating is not your goal to meet when the tire heats up. It's a guide as to the load capacity of that tire at cold temperatures. Dependent upon air and road temps it is entirely feasible to run pressures that exceed max inflation. What you don't want is an overload situation where air pressure is insufficient to carry the load. That's why we get the blanket statements from Airstream and Tire retailers to use max sidewall pressure. That insulates them from liability somewhat since they have no idea of the load you will subject these tires to.

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Old 05-20-2015, 02:23 PM   #32
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Originally Posted by jcanavera View Post
That's why we get the blanket statements from Airstream and Tire retailers to use max sidewall pressure. That insulates them from liability somewhat since they have no idea of the load you will subject these tires to.
I assumed this much. It's pretty common.
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Old 05-20-2015, 03:05 PM   #33
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Quote:
Originally Posted by Phoenix View Post
Just my opinion: Airstream, Discount Tire, Costco and others recommend "maximum sidewall pressure" for trailer tires. For load range E tires, that's 80 psi.

I have ridden in our 2005 19' Bambi at highway speeds, with OEM GYMs inflated to 65 psi and Michelin XPS Ribs inflated to 80 psi; and I could tell no discernable difference in ride.
Why in Gods name would you do that? If a C rated GYM could run at 65 lbs. Why would you run an E rated tire any higher under the same load.

Get the trailer weighted and set the tires to the inflation chart not to the recommendation of someone that may not even be able to spell inflation.
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Old 05-20-2015, 06:41 PM   #34
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Re: Tire inflation pressures

HowieE, I assume the 65 psi inflation pressure that you reference is for a LR-D GYM. On your 34-foot, triple-axle Excella, the per-tire load is about 1,500 pounds.

I have a 19' Bambi that weighs 4,500 pounds on a single axle; so my per-tire load is about 2,250 pounds, which is 50% higher than the tire load on your Excella.

Note: Weights are approximate due to differing tongue weights and the unknown number of barbells and anvils we may both have hidden in our Airstreams.

In the first few years of ownership, three of six ST tires failed on our Bambi. The two GYMs were LR-D, inflated to 65 psi; and the LR-E Maxxis tire was inflated to 80 psi.

Four years ago, we switched to 16" wheels and LR-E LT tires, which are inflated to 80 psi; and in the past 25-30,000 miles since switching, we have had absolutely no tire problems.

For me, this is enough proof that ST tires are unsuitable for my Bambi, and 80 psi is the proper tire pressure (for LR-E tires).

I should note that we live in the desert southwest where summer temperatures often reach 118+. Others who travel in cooler climes and have lower per-tire loads may have better luck with ST tires and/or lower tire inflation pressures. However, the Airstream Tire Failure Poll would seem to indicate otherwise, with an approximate 50% failure rate reported for ST tires, 75% of which were inflated to the maximum sidewall pressure.
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Old 05-20-2015, 07:35 PM   #35
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How to weigh an Airstream

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Originally Posted by Re-Pete View Post
Can anyone post links to a thread/s on how to weight a TT (Airstream) including the individual tires? I've not done this before, and am a bit intimidated by the process.
Configure your Airstream as if you are going camping and if your area has a Farmers Coop call and ask if they have scales. If no Coop then call your local solid waste landfill who will have scales. Call ahead and ask if they can weigh your trailer and if so, pull your tow vehicle forward and off the scale leaving just the AS tires on the scale ramp. This will give you the actual weight adjusted for your hitch displacement. If your hitch/TV arrangement doesn't sit level, as mentioned in a previous comment, you may call your State's DEPARTMENT OF motor Vehicles and ask if you can weigh your AS at a DMV weigh station near you. If there is a nearby Airplane repair shop they should be able to weigh your AS for a fee.
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Old 05-20-2015, 08:31 PM   #36
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Configure your Airstream as if you are going camping and if your area has a Farmers Coop call and ask if they have scales. If no Coop then call your local solid waste landfill who will have scales. Call ahead and ask if they can weigh your trailer and if so, pull your tow vehicle forward and off the scale leaving just the AS tires on the scale ramp. This will give you the actual weight adjusted for your hitch displacement. If your hitch/TV arrangement doesn't sit level, as mentioned in a previous comment, you may call your State's DEPARTMENT OF motor Vehicles and ask if you can weigh your AS at a DMV weigh station near you. If there is a nearby Airplane repair shop they should be able to weigh your AS for a fee.
lol, or just go to any CAT scales at any one of the dozens of truck stops in the country.
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Old 05-20-2015, 08:48 PM   #37
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Quote:
Originally Posted by Phoenix View Post
HowieE, I assume the 65 psi inflation pressure that you reference is for a LR-D GYM. On your 34-foot, triple-axle Excella, the per-tire load is about 1,500 pounds.

I have a 19' Bambi that weighs 4,500 pounds on a single axle; so my per-tire load is about 2,250 pounds, which is 50% higher than the tire load on your Excella.
No actually the Michelin tires on my 8,900 lbs 34 are inflated to 45 lbs. and that is 5 lbs more that the chart calls for. I run then slightly high so if I have a flat I can run in and still have enough pressure in the tires to carry the load.

I am going to assume you are running 225 75 16 E and if that is the case your tire pressure should be 60 lbs for that weight. Since Michelin does not make a D rated tire and a C rated would be pushing is at 4,000 lbs.
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Old 05-20-2015, 09:00 PM   #38
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lol, or just go to any CAT scales at any one of the dozens of truck stops in the country.
Lol, that works too. I like options. Seems you have all the answers. You win the Internet for 5 minutes.
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Old 05-20-2015, 09:14 PM   #39
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My question is, can one determine the correct tire pressure based upon how arm the tire gets in use? It would seem to me, if the tire were under inflated, it would become much warmer, way to hot to touch. Correct inflation would result in the coolest running temperature.
Absolutely. This conversation is ongoing on this forum. I do not know your tire brand info but I have Michelin MS/2 16" and there is a chart for both the MS/2 and Rib. That chart, which I have posted several times is based on load per axle. Contrary to popular belief, the chart for the E rated 16" tires goes as low as 30 PSI up to 80 PSI for the max load. Temperature sensors can be used to dial in the best PSI. If tires are too low, the temperature rises quickly and stress is on the sidewall. Too much pressure for the load and the pressure is transferred to the tread and the radial tire footprint is misaligned. It is not good either way. I have never run tires at max PSI on any vehicle. It rides rough and violates manufacturer guidelines AND gives no leeway for the tire.

CAT Scales: In the "RV Handbook 4th Ed. by Dave Solberg, p.73, they provide a diagram for trailer weighing showing how to use CAT scales. "pull up until the truck front axle mirrors are past the end of the first scale plate. The rear axle and trailer jack should then align with the second plate while the trailer axle(s) are on the third plate. Small trailers may have to adjust position."
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Old 05-20-2015, 09:42 PM   #40
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I've had 16 " Michelin s on our 30' Classic for 2 years and about 10000 miless. I run 80 psi cold.
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Old 05-21-2015, 06:38 AM   #41
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CapriRacer, does this mean that if we run our Michelin 16" LTX tires on our Airstream at 60 psi, rather than the 80 psi maximum pressure indicated on the sidewall, that is a correct pressure if it passes your pressure test procedure?

That seems to be in conflict with another tire engineer who has recently cautioned here that any tire used on a multi-axle travel trailer with lowered pressure is more likely to experience tread separation from sideway scrubbing when turning the trailer, so we should always use the maximum sidewall indicated pressure.

Or are you suggesting we should always use the maximum sidewall indicated pressure, and then use your pressure test procedure to ensure it is enough? I suppose the two tire engineers would be in agreement then?

The correct tire pressure for our Airstream remains unclear to me.

cheryl
Cheryl,

I think Roger and I are on the same page. RARELY, will the final answer be significantly less than the maximum.

At the same time, I am recognizing that it is POSSIBLE that all the charts and calculations result in something LESS than the maximum and the test is a way to confirm.

I can understand why the correct pressure is unclear. What should have happened, didn't. That's why we are going through all this - to do what should have been done so that it is transparent to the end user.
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Old 05-21-2015, 12:10 PM   #42
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Thanks to all for the info

This has been very helpful, and I will do the cold/hot inflation test next week. As I carry a compressor in the back of my truck, I can make adjustments at anytime by simply starting up the generator also in the truck bed.

Thanks much for all the help.
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