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Old 10-10-2012, 07:34 AM   #43
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Originally Posted by rp709 View Post
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.
I am going to disagree with this.

Given that there have been so many tire failures with 15" tires, my standard recommendation is to go up in load carrying capacity. I think it is wishful thinking that using a Load Range E tire at Load Range D pressures is somehow better.

And given that so many folks don't really know what the individual tire loads are (many think in terms of axle load) - AND - that the table should be used whith a safety margin added (something most folks don't know) - AND - there isn't any harm done by using the higher pressures, I can't say with a straight face that anyone should use less than the max pressure listed on the sidewall.
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Old 10-10-2012, 08:12 AM   #44
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I replaced my 15" GYM Marathon ST (max recommended pressure on my Airstream tire pressure tag is 65#) with the same Michelin tires and 16" wheels used by Airstream on the Eddie Bauer model.

Unsure of the correct pressure to use, I looked at the tire pressure tag on a 25' Eddie Bauer model at the dealership, same trailer size as my Flying Cloud. It said correct tire pressure is 80#, so that is what I inflate my Michelin LTX tires to.

This may not apply to every Airstream ever built, but it would appear Airstream is recommending using the maximum pressure printed on the tire in this case. However, you must ensure the wheels are also rated for the pressure you use.

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Old 10-10-2012, 09:26 AM   #45
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Michelin LTX Pressure

Doug K -

Thanks for reporting on the Airstream recommended pressure on the Eddie Bauer for the Michelin LTX. Since I switched to the 16" Michelin LTX on my 27FB Safari I've been wondering what pressure to run. Based on the recommendation of my tire shop I've been running at 75 lbs, which seems okay. I'll now consider taking it up another 5 pounds.
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Old 10-10-2012, 10:00 AM   #46
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Recommended trailer tire inflation pressure from several sources:

"Always inflate trailer tires to the maximum inflation indicated on the sidewall." -- Discount Tire

"I would strongly recommend you put in the maximum tire pressure listed on your trailer tires." -- eTrailer.com (expert's reply to question on trailer tire inflation pressure)

"Most trailer tires should be run at their maximum inflation pressure. Consult the maximum pressure rating on the sidewall of the tire, and inflate your tires to this amount when the tires are cold." -- Haulmark Trailers

"Most trailer tire manufacturers recommend adjusting the air pressure to the maximum pounds per square inch (PSI) listed on the sidewall of the tire." -- Cedar Rapids Tire (Internet tire sales)

"Maintain pressure at the maximum PSI recommended on the tire’s sidewall for cool running, load-carrying ability and lowest rolling resistance." -- West Marine

"...check inflation prior to going on the road. It’s marked on your tire." -- BoatUS

" It's a common practice for RV owners to lower tire pressure in their search for a smoother ride. This is not only dangerous, it's relatively ineffective, as the difference in ride quality is not significant." -- Goodyear

==============

For more "maximum sidewall inflation pressure" recommendations, just search the Internet.

Note: Airstream also recommends using the maximum sidewall inflation pressure.
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Old 10-10-2012, 10:14 AM   #47
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Quote:
Originally Posted by Morgan guy View Post
I have a 2007 AS Classic 27'. It has a GVWR of 9000 lbs. I havve 4 Maxxis load range E tires rated at a capacity of 2830 lbs/ 80 Psi, for a total load of 11,320 lbs. With an excess capacity of 2,320 lbs, I would like to run a lower air pressure than 80 lbs to give a softer ride to the trailer. Does anyone know how the pressure adjustment affects the load capacity, in other words, what can I safely lower the pressure. The label on the trailer says 65 lbs but doesn't reference what load range of tire.
The chart at this weblink should give you what you are looking for.
https://www.maxxis.com/Repository/Files/m8008load.pdf
I use load range E tires inflated to 60 psi, due to max 65 psi inflation limit on my wheels. I have had no problems, yet. I have towed about 10,000 miles on these tires in the last 18 months in mostly cool weather. But, my Safari's GVRW is 7,400 lbs.
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Old 10-10-2012, 12:20 PM   #48
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The chart at this weblink should give you what you are looking for.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

https://www.maxxis.com/Repository/Files/m8008load.pdf.
This post is not directed at A W Warn. He just happened to post the link.

Please read carefully what the title of the chart says:

"TIRE LOAD LIMITS (LBS) AT VARIOUS COLD INFLATION PRESSURES (PSI)"

It says nothing about, nor does it equate to, recommended pressure at a given load. The purpose of this chart to define the absolute maximum load you can carry at a given pressure. If you are at or close to that load, you are driving on the edge of safety.

If you want the recommended pressure look at the quotes in post #46 or research your own. Those of you who feel that you are saving your trailer from damage, keep in mind that is what the suspension system is designed for. I personally am not willing to go any closer than absolutely necessary to the safety limit of anything in order to protect my trailer from something that has not be proved as a problem,
especially when there are so many arguments for using the max inflation pressure. Keep in mind that these maximum inflation values are "cold" and take into account the extreme conditions they may encounter in use. Yes, bumpy roads can cause damage to the trailer, but those same bumpy roads will also cause more flexing of the tire at lower pressures, so your chance of a catastrophic tire failure are also increased. I will choose the possible minor shock damage. If you experience anything worse than minor, you are driving too fast for the road condition.

Ken
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Old 10-10-2012, 04:04 PM   #49
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one other factor is traction. the tire will bulge in the center if overinflated. it will leave a narrow skid mark and take longer to stop in severe applications. under-inflated tires will ride on the edges and also take longer to stop. pick your poison.

it seems that with trailer tires failing so often forces people to pick the portion of tire performance they feel comfortable.
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Old 10-11-2012, 03:42 PM   #50
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high pressure

When tires get hot the pressure builds in them. This puts more strain on the sidewalls leading to failure. If the tire is always inflated to the maximum, then it will be under greater strain all the time, especially when temperatures rise. If the tire is inflated to less than the maximum, there is a greater margin before the tire is over stressed. If the lower inflation pressure does not lead to excessive heat (which is also a function of the load on the tire) then there is a clearly greater safety margin. The maximum pressure on the sidewall is necessary only to carry the rated load. Why are there inflation and load tables? Just a thought?
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Old 10-11-2012, 04:02 PM   #51
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When tires get hot the pressure builds in them. This puts more strain on the sidewalls leading to failure. If the tire is always inflated to the maximum, then it will be under greater strain all the time, especially when temperatures rise. If the tire is inflated to less than the maximum, there is a greater margin before the tire is over stressed. If the lower inflation pressure does not lead to excessive heat (which is also a function of the load on the tire) then there is a clearly greater safety margin. The maximum pressure on the sidewall is necessary only to carry the rated load. Why are there inflation and load tables? Just a thought?
Your logic is interesting.

Tire temperature builds when tire walls flex. Tire walls flex more when pressure is lower. If inflated to the max cold air pressure, the tire will not flex as much, they won't heat up as much, and the pressure won't increase as much. Generally tires don't fail because they pop like an over inflated balloon. Generally, aside from road hazards, tires fail because they overheat from insufficient pressure. This higher temperature causes a breakdown of the materials they are constructed with. These weakened tires will eventually come apart or rupture.

There are inflation and load tables so you can tell how much load a tire can support at a given pressure. As far as trailer tires are concerned, it is my strong belief that the tables are not intended to be used backward.

Ken
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Old 10-11-2012, 06:07 PM   #52
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I have decided there is no good answer out there for the tables, so I am looking at this another way.

Baseline: 30' Classic, Michelin LTX M/S LTs, 16" with right at 8000# on the axles, so 2000lbs on each tire (roughly)

I was running at 65#, but it always bothered me that I would see a 7 - 9# rise in tire pressure and the very same tire on the TV would see a 4# rise. This is what I have observed in virtually all the company vehicles I have driven since TPMS has been in the cars.

I also began looking at tire temps with the infrared between the lugs at the edges and center.

Here is what I have found so far:

65psi = 7 - 9# rise in pressure; temps 45 - 50* above ambient and within 1 - 3* across the tread. Very consistent on all 4 tires.

70psi = EXACTLY the same results!!!!

I only have one more trip this fall, before winterizing, so I will jump to 80psi and re-measure.

I can think of no reason why I should not see the same kind of temp rise as the TV.

BTW; it is my observation that the temp readings on the outside of the carcase indicate only about 1/2 of the temp rise on the interior of the tire....where it matters. A 9psi rise indicates a 90* rise over ambient...both by my observations over time and backed up by TireRack.com......1psi=10* change in temp.
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Old 10-11-2012, 06:35 PM   #53
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Mamimum sidewall pressure =

A] Lowest probability of having tires torn off the rim in ordinary trailer maneuvers.

B] And lowest probability of internal tire damage due to greatest resistance by the sidewall.

What goes for cars, etc, is not the same for trailers.

The pleasure of regular vehicle enthusiast forum reading is the opportunity to modify practice, not just buy the latest & greatest gizmo for the vehicle. In this case it is the attention of CapriRacer on these forums, and the blog of Tireman9 on the Net: two tire engineers giving background for advice in light of RV tire problems across the spectrum of type. Their thread on RV.net gives all sorts of info (and linked here; see "Revised Tire Thread" from earlier this year).

.
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Old 10-12-2012, 09:10 AM   #54
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temp rise

Good info on temperature rise observed. For some reason trailer tires seem to heat up faster than tv tires. Maybe this is why there are ST trailer tires in the first place--to resist this with stiffer sidewalls etc. I would like to know where the '65 mph' rating came from and why it stands today?
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Old 10-12-2012, 09:19 AM   #55
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Originally Posted by rp709 View Post
Good info on temperature rise observed. For some reason trailer tires seem to heat up faster than tv tires. Maybe this is why there are ST trailer tires in the first place--to resist this with stiffer sidewalls etc. I would like to know where the '65 mph' rating came from and why it stands today?
I have noted this as well, but there is no logical reason for it, on a straight road, other than load vs. pressure. Airflow around the tire could be less than a TV, but I don't think enough to make as drastic difference as 4psi rise in TV and 9psi rise in AS. We'll see what 80psi does.

BTW, I saw the same or very similar rise in my GYMs, before the LT swap.
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Old 10-12-2012, 04:03 PM   #56
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Michelin's response to my inquiry

October 12, 2012


Hello,


Thank you for your email. We welcome the opportunity to serve you.

In regards to the email you sent stating:

---------------------------------------------------------------------
I do not find a ST rated Michelin tire, nor do I find any recommendation for using LT tires on a RV travel trailer on this website.
What Michelin tire is recommended for a RV travel trailer?
Does Michelin warranty LT tires used for RV trailers?
---------------------------------------------------------------------

ST (Special Trailer) tires are constructed with heavier materials in the casing as compared to passenger rated tires giving the ST tires more strength and load carrying capacity. ST tires also have a stiffer sidewall and flex less making them more compatible with the trailerís suspension system.

We do not recommend using passenger tires on trailers that specify ST tires. If the trailer manufacturer calls for ST tires, it is important to replace with ST tires in order to maintain the load requirement.

Unfortunately, we do not have anything that is equivalent to an ST rated tire.

We appreciate your business and thank you for choosing Michelin.

If we can assist you further, please respond to this email or call us at 1-800-642-4354 (toll free) between 8:00AM and 8:00PM Eastern Time Monday through Friday or between 8:30AM and 4:30PM Eastern Time on Saturday.

Sincerely,

Consumer Care Department
Certified Michelin Product Expert

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