Michelin LTX M/S2 - Inflation Preferences

[BoldAdventure]

Please don't chop off my head. I know this has been discussed here and there with a lot of debates.

I am running the Michelin LTX M/S2 LT225/75R16 like many others, and for some time I was inflating to 70psi cold. And usually they'd heat up to 75psi.

I'm not sure how I arrived at 70psi, perhaps something I saw here on Airforums. I was reviewing the Inflation Tables (which I've attached here to this post) and decided to lower the pressure to 60psi. Which is still over the weight rating for my axles at 4380lbs. I wanted to experiment with getting a softer ride for the Airstream.

We drove 163 miles today from the middle of the Mojave Preserve in CA to Parker, Arizona. The tires warm all went to 67psi and maintained that pressure, I checked at several intervals.

The load table would seem to suggest I can run 50 psi. And the original Goodyears are suppose to be inflated to 50psi, as printed on the placecard on the side of my Airstream.

I just thought I'd throw this out there to get some opinions, negative or positive, doesn't matter. Do you run these tires based on the load tables, or do you just inflate to maximum? Share your thoughts.

I'm thinking about experimenting further, but I also want to minimize risk.

[AWCHIEF]

I inflate to manufactures recommendation.

[Al and Missy]

I have been running mine at 75 psi because at about 74 psi they have the same load carrying capacity as the original ST225/75-15s. Several on here have expressed the opinion that using the load tables that were intended for the standard use of the tire (light trucks) may not be appropriate on tandem axle trailers due to the twisting stresses placed on tires on tandem axle trailers when turning. That is why I have not gone below the pressure that results in the same load carrying capacity as the original tires.

By the way, the original tires were WAY overkill for my GVW (6300#). I don't know why Airstream used them instead of lower load range or smaller tires, but I chose tires with the same load capacity.

Your experience would seem to say that there is more pressure buildup and therefore more heating at 60 than at 70. If that pressure rise is typical, I'd be tempted to stay at 70.

Al

[dkottum]

I like 65-70 psi because many Airstreamers here are using it with no issues. My concern is also a soft ride for our Airstream balanced against any risk. I don't see any risk at these pressures, based on other and our own experience. I would like to run them a little less, but I don't see the experience here to back it up yet.

[Ted S.]

Originally Posted by AWCHIEF

I inflate to manufactures recommendation.

Which is what? I never understood that, looks like he has a whole chart of psi options. Are you saying to inflate until the tires are at your load capacity? Any saftey factor?

When I go to Michelins next year, I'm going with 80 psi...

[Wanderer2604]

I run the same tires on my 07 25' Classic at 65 psi cold.

[ROBERT CROSS]

Never mind..... these are on the Burb.
AS at 70psi

Bob

[dkottum]

Originally Posted by Ted S.

Which is what? I never understood that, looks like he has a whole chart of psi options. Are you saying to inflate until the tires are at your load capacity? Any saftey factor?

When I go to Michelins next year, I'm going with 80 psi...

Ted, I started with 80 psi as well, then began to be concerned about roughing up the Airstream. I noticed some people have loose hinges and cabinets, things getting knocked around and broken while some people do not.

Thinking of how much rougher our truck rides at maximum rather than normal reduced pressures, I decided to start looking at lower pressures for the Airstream's 16" Michelins.

[Hamish]

From a dkottum reference on 10-09-2014 to a 2013 discussion on the same topic. We run at 55psi with a 2014 EB 28 foot.

Originally Posted by dkottum

On 11-03-13 Andrew T. wrote:

We have the best results carrying the correct tire pressure for the load the tire is carrying. The attachment is the RV load inflation table from Goodyear's website.
Here are the pressures for a 225/75R x 16 LT:

80psi 2680 pounds,
65psi 2335 pounds,
50psi 1940 pounds,
45psi 1790 pounds,
40psi 1650 pounds,
35psi 1500 pounds.

To use this chart you really should weigh your combination connected & loaded for travel on a sectioned scale.

For example the last Eddie Bauer I weighed with a customer was 6700 pounds on the axles (motor cycle inside) or 1675 pounds per tire. Generally I will add 10% to that number for variences in side to side load and the possibility that the scale is out a little so 1850 pounds per tire. Using the chart you could call it at 47 PSI but we went with 50 psi. 50 PSI has several advantages over 80 PSI; a smoother ride for the Airstream, shorter stopping distances espessially when wet and more even tread wear.

Some trailers & fifthwheels with corners are built with 225 Marathons right at their limit just over 10,000 pounds on tandem axles. In those cases we use the 225/75R x 16" LT with 80 psi.

From 1971 - 1984 a factory option on a new Airstream was Michelin 7:00 x 15" load range "C" tires. There were thousands of Airstreams built with these and tire trouble was very rare. I know many would say those trailers were lighter but actually many were not. The brochure weights in those days did not include options and everything was an option. By the time you added awnings, ac, double pane windows 2 door fridge etc. they weighed about the same as the new ones. Generaly 70's units tow a little easier because they are narrower and little more aerodynamic.

Years ago we could buy 225/75 x 16 Michelins in load range C which was a better match for most Airstream's but they are no longer available.

I know this is confusing and it is always easier to assume that bigger and heavier and more pressure has to be better but everthing has its compromizes.

Andrew T
__________________
Andrew Thomson
Can-Am RV Centre | #1 Airstream Dealer in Customer Satisfaction Worldwide | Your Full-Service RV Dealer

London, Ontario

S&K

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[BoldAdventure]

Originally Posted by Al and Missy

I have been running mine at 75 psi because at about 74 psi they have the same load carrying capacity as the original ST225/75-15s. Several on here have expressed the opinion that using the load tables that were intended for the standard use of the tire (light trucks) may not be appropriate on tandem axle trailers due to the twisting stresses placed on tires on tandem axle trailers when turning. That is why I have not gone below the pressure that results in the same load carrying capacity as the original tires.

By the way, the original tires were WAY overkill for my GVW (6300#). I don't know why Airstream used them instead of lower load range or smaller tires, but I chose tires with the same load capacity.

Your experience would seem to say that there is more pressure buildup and therefore more heating at 60 than at 70. If that pressure rise is typical, I'd be tempted to stay at 70.

Al

Yes, these are some of the thoughts I had too about the intended use in relation.

As for pressure buildup; does anyone know what is the proper "cold" temperature. It was in the mid 50's this morning when I set this pressure, and then by the time we got here it's 80.

70 has certainly worked out, just been curious about this topic for reasons stated above. Good discussion so far. Lots to ponder.

[Al and Missy]

Originally Posted by BoldAdventure

Yes, these are some of the thoughts I had too about the intended use in relation.

As for pressure buildup; does anyone know what is the proper "cold" temperature. It was in the mid 50's this morning when I set this pressure, and then by the time we got here it's 80.

70 has certainly worked out, just been curious about this topic for reasons stated above. Good discussion so far. Lots to ponder.

Good point. The 30 degree rise in ambient will change the "cold" temperature. When did the rise from 60 to 67 occur, and what was the outside temp at that point? If you dont have a TPMS you may not know that. I typically see about 79-80 from 75 when driving but I havent had much ambient change.

Al

[dkottum]

We have often left home in Minnesota in freezing temps, heading south and encounter much warmer weather in a few days. This affects tire pressures but I quit worrying about it until I am in more stable day-to-day travel weather, then I may adjust pressures accordingly. But I often wonder if too much is made of a few pounds one way or the other.

[paulken]

I have had my tires almost 2 years and for the last year and half I have been running 60 psi. I have not checked the psi. when warm, I usually check the temp at the hub and tire. With 6000 miles I have not seen any wear problems on the tires.

From what I am reading here I could drop down to 55 psi without any worry.

[BoldAdventure]

Originally Posted by dkottum

We have often left home in Minnesota in freezing temps, heading south and encounter much warmer weather in a few days. This affects tire pressures but I quit worrying about it until I am in more stable day-to-day travel weather, then I may adjust pressures accordingly. But I often wonder if too much is made of a few pounds one way or the other.

I thought I read somewhere from Tireman6 or whatever his name is, that a tire's PSI shouldn't increase more than 5-8psi. If it's increasing by 10 or more psi then it's underinflated, overinflated or overloaded. At least, this has been the measure I've been using in my head all this time. I could be totally wrong.

Kind of the reason for this thread.

[dkottum]

Bold, I remember that 10% advisory as well. I don't think he was considering changes in ambient temperatures as we are talking about, maybe starting the day at 25 degrees outside and 75 degrees the next day.

The 10% change advisory in stable ambient temps as a potential problem certainly sounds reasonable.

[Ted S.]

Let's not forget about elevation change. I mean why not just trash our entire Saturday night taking about trailer tires.

So when I left Boston, my tires were where they needed to be, but 9000' higher on the Big Horns....

[Alphonse]

Here is Tireman9's blog. His recommendation is fill it to the sidewall spec.
RV Tire Safety: "Interply Shear" and other Techno Babble

By the way, CapriRacer, another tire engineer, who posts here from time to time gives the same advice.

Here is a very good thread where both these gents weighed in on Cold Inflation Pressure (CIP). Thread was started by Tireman9 and CapriRacer also pipes in with a very good point.
http://www.airforums.com/forums/f438...re-140122.html

[dkottum]

I like to consider the tire engineers input into these discussions, and safety is paramount, but I don't think they are as concerned about a stiff ride roughing up my Airstream as I am.

So I've taken that and other Airstreamers' experience as all good advice and decided on 65-70 psi as something we can use, still thinking of a little less.

[TheDuke]

For the best tire life, mileage, wear and over all performance, you should always run the max pressure listed on the sidewall. Tires that are underinflated run at hotter temps than tires that are inflated to max pressures. Many tires that blow out have usually been underinflated at some time in their life. Yes, you may notice a slight degradation in the ride, however you will have less sway and a better overall experience with your tire. For the best overall tire performance have nitrogen installed at max pressure. LT tires can even be inflated 10% over the sidewall max pressure per manufacturer specs for heavy hauling. I have never done so, because I never overload a tire, and I have never had any trouble.

[BoldAdventure]

Originally Posted by TheDuke

For the best tire life, mileage, wear and over all performance, you should always run the max pressure listed on the sidewall. Tires that are underinflated run at hotter temps than tires that are inflated to max pressures. Many tires that blow out have usually been underinflated at some time in their life. Yes, you may notice a slight degradation in the ride, however you will have less sway and a better overall experience with your tire. For the best overall tire performance have nitrogen installed at max pressure. LT tires can even be inflated 10% over the sidewall max pressure per manufacturer specs for heavy hauling. I have never done so, because I never overload a tire, and I have never had any trouble.

If this is true, why then are manufacturers putting vehicles on lots with under inflated tires?

There seems to be no consensus or standard.