Michelin LTX M/S2 - Inflation Preferences

[CapriRacer]

Originally Posted by dznf0g

Do you need to account for ambient temperature rise when noting percent rise throughout the day? As well as sun load side of trailer? .......

Yes, you need to account for any change in ambient conditions - morning vs afternoon, sea level vs mountains, etc.

[Wayne&Sam]

This is getting a bit obsessive, bordering on the nitrogen discussion.

A dog peed on my left front tire. Do I need to adjust the tire pressure in that tire to compensate for it?

[Alphonse]

Originally Posted by Wayne&Sam

This is getting a bit obsessive, bordering on the nitrogen discussion.

A dog peed on my left front tire. Do I need to adjust the tire pressure in that tire to compensate for it?

You posted, you must like it!

[BlackAces]

When using replacement tires that do not conform to the inflation pressures or inflation pressure charts for the OE tires, you need to go to the trailer's certification label/tire placard and determine how much load capacity was provided by the OE tires recommended inflation pressures shown on the labeling. Then, using the inflation chart for the replacement tires, determine the inflation pressure needed to provide, as a minimum, the load capacity the OE tires provided. Tire industry standards, under normal circumstances, will never recommend less.

[switz]

That would make sense if Airstream used different tries for different weight trailers. They install the cheapest tire out there, the GoodYear Marathon ST225/75R15D rated 2,540 pounds @ 65 psi and 28.3" in diameter. Those tires are installed on the heaviest load trailer, the 20' Flying Cloud with a 5,000 load rated axle and GVW as well as trailers with much lower axle loads like the 25/26/27/28 models using the same 3,800 pound rated axles.

The 20' model trailer would have a theoretical tire loading of 2,500 pounds per tire (less the tongue weight). The 25' models with a GVW of 7,300 pounds spread over four tires would have a theoretical tire load of 1,825 pounds (less the tongue weight).

So the cost savings of Airstream stocking one 15" tire out weighs what might be the advantage to a more appropriate rated tire based upon the load.

The RV industry uses the cheapest possible tire since their concern is only to get the trailer to the dealership lot. They often install older ties on new trailers. Our 2014 31' Classic (with 5,000 pound rated axles) had a 13 month old GYM installed on the line.

Unfortunately, Airstream sources the cheapest parts even though their products command premium prices. Examples are the plastic cabinet latches and the electrical outlets.

I read enough here starting in September 2012 on the tire issues associated with the GYM ST tires. That information plus personal experience with both a tandem motorcycle trailer and a single axle motorcycle trailer convinced me that I would need to replace the OEM ST tires with better quality ones.

Obviously, Airstream is thinking so as well since they installed the 16" Michelin LT225/75R16/E LTX M/S2 tires on the 27FB Eddie Bauer with a 7,800 pound GVW (that GVW exceeded the two 3,800 pound axle ratings). I saw these tires in October of 2012 along with the SenDel T03-66655T wheels for sale at the factory with a display just after the door when entering the Service center. They were recommended for the recent 25' and longer trailers.

Starting in 2015, the Classic 31' trailers come standard with the 16" tire and wheels captioned above.

I have used Michelin tires for nearly 50 years with no blow outs. I swapped out the OEM tires for Michelins as soon as any new vehicle was mine which usually resulted in better handling and ride. The switch to both the 15" and the 16" Michelins made perfect sense to me.

In my case, the 15" Michelin LTX (P) 235/75R15 XL tires have a higher load capacity (derated to 1,985 pounds) than the 14" GYM ST215/75R14C tires (1,870 pounds) that they replaced on the 23D and the 16" tires have a higher load rating (2,680 pounds) than the 15" GYM ST225/75R15D tires (2,540 pounds) they replaced. The replacement tires were mounted onto 15" SenDel T03-56545T wheels and 16" SenDel T03-66655T wheels which have the same visual appearance.

[sunahara]

Has anyone heard or tried the new Michelin Defender LTX? It has a higher load carrying capacity

[tjdonahoe]

Originally Posted by sunahara

Has anyone heard or tried the new Michelin Defender LTX? It has a higher load carrying capacity

Better look again,,

[Tireman9]

Comments on a few different topics seen in this thread. In no particular order.

"Cold Tire" or Cold Inflation Temperature does not mean you need to put your tires in the fridg. What is actually meant is not warmed up by either being driven on or exposed to direct heat source such as Sunlight. You want tires to be at Ambient temperature.
Definition: The ambient temperature is a non-specific phrase used to describe the outside temperature.
If you drive more than a couple miles then the tires have started to warm up and are not "at ambient". In general tire pressure will change by 2% fir each change in temperature of 10F. Does this mean you can't check your pressure if you drive 3.5 miles? Of course not. It just means the best time to check and set pressure in the most accurate manner is when the tires are at the same temperature as the surrounding air.

Minimum inflation pressure is what the tire needs to carry the load on that individual tire. The only accurate way to know that is to get a scale weight for each tire position. i.e. RF, LF, RR etc. If all you can do is learn the total load on an axle then you need to include a minimum margin of 3 - 5 % to compensate for side to side unbalance. PLUS If all you can do is learn the total load on all axles then you need also to include a minimum margin of 3 - 5 % to compensate for axle to axle unbalance.
This unbalance is based on measurements done with individual scaled under individual tires where it has been discovered that fewer than 2% of all RVs are found to have 50/50 weight split either axle to axle or side to side.

Special Conditions and consideration for multi-axle trailers. Every time you turn a corner, not just when backing into a tight campsite, you are placing significantly higher internal shear forces on your tire belts which are trying to tear the tire apart. If you Google "Interply Shear RV Tires" you can learn the technical background for these forces that can be 24% higher on your RV than if identical tires with identical loads and inflations were used on a motorhome.

Cold Inflation Pressure would refer to your personal goal based on knowing your personal tire loading plus appropriate margins. Just because the guy parked next to you has selected 63.5 psi for his RV does not mean that 63.5 psi is the CIP you should use. After all does he have more bowling balls in his collection than you do?

At a minimum you need to confirm your tires are not overloaded at CIP. This means getting on a scale and applying the unbalance factors if you can only get axle loading.

I would suggest that once you know the loads on your tires you add a minimum of 10% to the minimum inflation to establish your personal CIP, and if you want to get the best life out of your tires you should run the inflation molded on the tire sidewall to lower the Interply Shear forces on your tires.

Remember never exceed the max inflation or load rating of your wheels. You can check my profile homepage for info on my RVTireSafety blog that has over 200 posts on RV tires for more details.

[JamuJoe]

"So another question for this thread. When off-roading, I use my Staun tire deflators and take the truck down to 20psi. Nice, smooth ride. I would think this technique would work on the Airstream as well, since we are not on pavement, and traveling at very low speeds. Thoughts?"

I air down for off-road travel (2014 Jeep GC w/ air suspension) when I need the additional traction of a wider footprint in loose rock or sand (works well for snow as well). I wouldn't air down my Airstream tires (FC23FB upgraded to 15" Michelin LTX) from the 50psi that I carry, as I wouldn't want to sacrifice even an inch of clearance when off road. We've taken the trailer into some pretty rough places with no ill effects, save the microwave rattling loose.

If only the Airstream had an adjustable air suspension like the Jeep.

Safe Travels,
Jamu Joe

[BoldAdventure]

Originally Posted by JamuJoe

"So another question for this thread. When off-roading, I use my Staun tire deflators and take the truck down to 20psi. Nice, smooth ride. I would think this technique would work on the Airstream as well, since we are not on pavement, and traveling at very low speeds. Thoughts?"

I air down for off-road travel (2014 Jeep GC w/ air suspension) when I need the additional traction of a wider footprint in loose rock or sand (works well for snow as well). I wouldn't air down my Airstream tires (FC23FB upgraded to 15" Michelin LTX) from the 50psi that I carry, as I wouldn't want to sacrifice even an inch of clearance when off road. We've taken the trailer into some pretty rough places with no ill effects, save the microwave rattling loose.

If only the Airstream had an adjustable air suspension like the Jeep.

Safe Travels,
Jamu Joe

I do the same, usually 18psi on mine. I think if you run 80psi taking it down to 50 might work.

[Tireman9]

Originally Posted by dznf0g

From prior posts in other threads, ambient temp is about 1 psi difference for every 10* change...but I don't recall the discussion relative to pressure rise (10% max) with any reference to ambients. I do recall that pavement temp was not considered significant with a rolling tire and airflow around it.

Sorry you are working from a publication of passenger tire pressure change. The actual change is about 2% for each change of 10F of the tire internal temperature.
I published the math proof on my blog.

Ambient change will affect the rate of heat build or drop as heat energy flows from hot (usually the tire) to cooler (usually the surrounding air.

The only time to get a meaningful tire pressure is when the tire is at ambient. This basically means after the tire has been stopped for a couple of hours and not in direct sunlight. It will take about 2 hours for a tire to reach Ambient as rubber is an insulator so heat flows out slowly and the area of concern is internal to the tire structure which can be 1/2" deep inside the tire shoulder area.