"LT" tire pressures on Expedition

[Rustycamperpant]

I moved up from "Heavy Load" tires on my Expedition to real "LT" tires. Max air pressure on the new tires is 80#, max pressure on the heavy load tires was 50#. I always ran my other tires at max pressure when towing my TT.

I talked to the tire installer and asked him what they set the pressure at and he responded, "To whatever is specified on the door sticker". This will be in the 36 - 38# range.

What do you all do? I was thinking all along I should run much higher pressure on the LTs just like I did on the heavy load tires. Thanks in advance...

[Ralph_Cramden]

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[CapriRacer]

Truncating all the previous posts:

Groover wrote:
What you say makes a lot of sense to me as an engineer (though not a tire engineer). I would like to add that the rating on the side is a MAXIMUM pressure and a Maximum load so they need to be read in that context. Likewise, most wheels have a maximum pressure rating. If yours don't I would assume that it is no more than maximum pressure rating of the original tire. While I agree that wheels rarely fail I feel that there is a good reason behind the ratings.

One of the things that I believe causes confusion among consumers is that tire pressure vs weight capacity charts don't seem to be available for the tires we use. …..

They are available, but they are largely unneeded, because ALL light vehicles (cars, pickups, and the like) are required to have a vehicle tire placard which will list the original tire size and the specified pressure for that size - and all the tire maufacturers will tell you to use that.

The exception to that is when a different size is used, and that is a whole other level of complexity.

Groover wrote:
……. I can easily get them for the load range H tires on my motorhome but not for my pickup or any car. A while back I put high fuel economy tires on a Taurus and noticed that they were rated at 50psi instead of the 35psi on the original tires. That raised the questions in my mind of whether I had to use the higher pressure to get the advertised fuel economy benefits and were the wheels rated for it. I called customer service at Goodyear and they flat out refused to answer any questions and would only tell be to use the recommendations on the manufacture's sticker. …..

That's because if you used the same tire size, the vehicle tire placard IS their recommendation regardless of what the max pressure on the sidewall says - even for high fuel economy tires.

Groover wrote:
…... They also refused to discuss the pressure ratings of any specific tire but they did finally give me excerpts from a chart developed by that American Society of Automotive Engineers from who knows how many years ago. …….

Ah ….. Mmmmm. … SAE doesn't publish load tables. Tire Standardizing Organizations do and in the US it is The Tire and Rim Association and those tables are pretty much good forever - that is, they don't change over time.

Groover wrote:
……. When I pointed out that the chart had a lot lower pressure rating than the sidewall did for the fuel efficient tires at max load they said that going up to 10psi over was not a problem. …….

Yes, the load table is the load table for ALL the tire sizes listed in the table - even ones with higher max pressures.

Groover wrote:
…..Anyway, if you can help us find some data developed by engineers and testing instead of going by opinions I would appreciate it.

What kind of data did you have in mind?

[Groover]

CapriRacer wrote:
One of the reasons I love following these threads - even though I don't own a travel trailer - is posts like the one below:

falconbrother wrote:
I read whats on the tire and do that. My rule is: Do not exceed the manufacturer's specifications. People try to outsmart the engineer who designed things. I do what the engineer said do.

That's contradictory.

The engineer (That would be me!) says what is on the sidewall isn't a recommendation - that reading the sidewall isn't going to give you the answer.

And if you read my post further upstream correctly, you'll notice I didn't actually give a recommendation. I merely asked for additional information and made a statement about the relationship between P type tires and LT type tires.

What you say makes a lot of sense to me as an engineer (though not a tire engineer). I would like to add that the rating on the side is a MAXIMUM pressure and a Maximum load so they need to be read in that context. Likewise, most wheels have a maximum pressure rating. If yours don't I would assume that it is no more than maximum pressure rating of the original tire. While I agree that wheels rarely fail I feel that there is a good reason behind the ratings.

One of the things that I believe causes confusion among consumers is that tire pressure vs weight capacity charts don't seem to be available for the tires we use. I can easily get them for the load range H tires on my motorhome but not for my pickup or any car. A while back I put high fuel economy tires on a Taurus and noticed that they were rated at 50psi instead of the 35psi on the original tires. That raised the questions in my mind of whether I had to use the higher pressure to get the advertised fuel economy benefits and were the wheels rated for it. I called customer service at Goodyear and they flat out refused to answer any questions and would only tell be to use the recommendations on the manufacture's sticker. They also refused to discuss the pressure ratings of any specific tire but the did finally give me excerpts from a chart developed by that American Society of Automotive Engineers from who knows how many years ago. When I pointed out that the chart had a lot lower pressure rating than the sidewall did for the fuel efficient tires at max load they said that going up to 10psi over was not a problem.

Anyway, if you can help us find some data developed by engineers and testing instead of going by opinions I would appreciate it.

[CapriRacer]

One of the reasons I love following these threads - even though I don't own a travel trailer - is posts like the one below:

falconbrother wrote:
I read whats on the tire and do that. My rule is: Do not exceed the manufacturer's specifications. People try to outsmart the engineer who designed things. I do what the engineer said do.

That's contradictory.

The engineer (That would be me!) says what is on the sidewall isn't a recommendation - that reading the sidewall isn't going to give you the answer.

And if you read my post further upstream correctly, you'll notice I didn't actually give a recommendation. I merely asked for additional information and made a statement about the relationship between P type tires and LT type tires.

[Grit_dog]

falconbrother wrote:
I read whats on the tire and do that. My rule is: Do not exceed the manufacturer's specifications. People try to outsmart the engineer who designed things. I do what the engineer said do.

Since you're trying to oversimplify it for the rest of us whom you appear to perceive as uninformed or not knowledgeable, go back and read the OP's posts and tell the class how your answer above is even remotely correct or "what the engineer said do."

I'll let you figure out why I said what I said.

And fwiw, to all the "do what the engineer said" folks, yes it is generally a safe practice, if not used out of context like falconbother's statement above.
However, being an engineer and also dealing with multiple engineers on a daily basis (but being on the practical application side of my industry, not the theoretical side), I can say heartily that "engineering" is an ever changing blend of the theoretical solution, the practical solution, the politics, the cost, the liability involved with the particular solution and the human opinion or error aspect.
Remember, believe nothing you hear and only half what you see...and trust but verify.

[APT]

You will have to test a few, trial and error. It will be a compromise of bounce/firmness, control, and tire wear. When I had LT tires on my half ton pickup, I ran 40 psi all around unloaded, and 50psi loaded/towing. My 3/4 ton Suburban with OEM LT-E tires recommends 50psi front and 60 psi rear. It weighs about 600 pounds more than your Expy empty, but had higher capacity. I would start 40psi empty and 50psi towing. I bet that is close for your situation.

[JIMNLIN]

Rustycamperpants wrote:
Oh, one other thing, my tires ahave always been the same OEM size, 275/55R20.

Listen to what CapriRacer says. He is a actual tire engineer (Barry Smith) and not just someone who would like others to believe he knows more.

Also the tire tech who told you to pump those E tires to door placard 38 psi should know better.
A LT tire psi needs to be around 50 psi (at a minimum) to meet the P tires load capacity which the P tire comes at around 35 psi according to tire pressure charts.

I would think 60 -65psi would be a good place to start then add more or less if needed.
Be sure and have the high pressure rubber stems installed in the wheels. The same type comes OEM on 3/4 and one ton trucks work fine.

[Rustycamperpant]

The tire is not vehicle specific, it as no idea if it is on a truck or a car or what the use is. Im confident that the cross reference of the actual OEM load criteria and the tire pressure chart I acquired is acurate. The tire reads 80# max psi, there is no way I need that. At 80# psi the tire is good for 3,042# per tire. At 7,500 GVWR, I do not need 12,168# capacity. Thanks for all of your input though, Im feeling pretty good about my choice....

[falconbrother]

I read whats on the tire and do that. My rule is: Do not exceed the manufacturer's specifications. People try to outsmart the engineer who designed things. I do what the engineer said do.

[Rustycamperpant]

Oh, one other thing, my tires ahave always been the same OEM size, 275/55R20.

[Rustycamperpant]

Thanks everyone. Rest assured I take most of what I read on these forums with a grain of salt. I have a guide titled "Determining Air Pressure For A New Tire Size" chart used by tire installers. I am confident of my 50-55# number. some of you have reassured me, thanks.

OEM tires are Pirelli Scorpion STR tires with a load rating of 111 (2,403# @ 44psi). These tires were squishy even with my pop up. I went to extra load tires with a load rating of 117 @50# psi and that was a major improvement. I used two sets of the 117 rated extra load tires.

My new LT tires are 117-120 load rating and at 80psi are good for 3,085# apiece. According to my recently acquired tire pressure chart inflating the LT tires to 50-55psi will give me load capacity of 2,335# per tire, nearly equal to the OEM Pirelli tires at the full 44psi (2,339# apiece). My goal is to have a much less "squishy" tow.

I am taking my first trip of the season in two weeks and it is a three hour tow one way. I am excited to see the difference the LT tires make. Thank you everyone for your input, all opinions are welcome!

[Grit_dog]

Also, not scientific, but general industry liability assumption....Yes ALL mfgs look to shave costs to increase margins, AND recognize liability as a big part of the risk matrix when designing a component or an entire product.
Tires and wheels get abused to no end, by EVERYONE, intentionally or not. And they're one of a few major components of a vehicle, that if they fail, at speed, have a high likelyhood of the literal fiery crash. Add axles, springs, brakes and steering components into this. No one dies if the AC quits working at 80mph. Someone does if the tire quits working at 80 mph.
Based on this and my previous post, there is a large factor of safety built into tires and rims.
Something to think about.

[Grit_dog]

To the OP, you'll likely not get close to the loads that require max pressure on an E load tire. The beauty of heavier tires than needed on a lighter duty truck/tow rig, is having the headroom for anything you'll carry or haul, stiffer sidewalls and tougher tires in general and longer tread life than the same P or XL rated tire.
Remember, it's air that holds the vehicle up, not tires. Air pressure needed is a function of load. Run whatever pressures you need for the weight you're carrying. Want a little softer ride, stay on the low end of the needed pressure for the weight. Want a more solid, better handling ride, adjust up some from what is needed.
Door stickers are 1 size fits all guidelines and liability coverage for the mfgs against those who don't understand and are sue happy. That is all.

BTW, I also believe, within reason, that you cannot blow up a good rim or valve stem, or tire for that fact. This is not scientifically proven, but rather from many years of doing more with less when needed. I routinely run 55-60 psi in the rear tires of half tons with 44psi "max" tires when towing heavy. Freeway speeds, mountain passes, frost heave riddled highways, etc. it works.

[Ralph_Cramden]

Ductape wrote:

Ralph Cramden wrote:

Rustycamperpants wrote:

Ductape wrote:
What is the pressure rating for your wheels?

Thats a good question , I dont know. I have the stock 20" wheels on my truck. I used a air pressure guide for a tire installer and it looks like if I use 50 - 55# of pressure I should get all the capacity I need. (in the neighborhood of 2,335-2,360# per tire).

I also read that if I go above 60# I may blow out my valve stems. I think I will run at 50, maybe 55#. The stiffer sidewalls should make a nice difference.

Be careful what you read on forums, especially RV ones. You're not going to blow out a valve stem by airing up to 60 lbs, or even 120 lbs, nor will your factory OEM wheel grenade. The pressure rating of your OEM wheel, if it even has one, will be more than the pressure any tire requires that will physically fit on it along with a substantial margin for safety/ error. Don't inflict yourself with a case of Rv board OCD.

I usually ignore idiots of this sort, but the OP and anyone else interested in uprating tires would do well to educate themselves as to the facts about wheel pressure and load ratings.

I'll have no further comment, life's too short to debate with people who are willfully ignorant and choose to provide dangerous advice.

Go down to your local tire place and ask the owner if he blows out many valve stems or has OEM wheels blow apart when he seats beads. I'll refrain from returning the favor and calling you an idiot, as you've made it quite clear that you are. Thanks for having no further comment. Go pop open another Ensure.

[Ductape]

Ralph Cramden wrote:

Rustycamperpants wrote:

Ductape wrote:
What is the pressure rating for your wheels?

Thats a good question , I dont know. I have the stock 20" wheels on my truck. I used a air pressure guide for a tire installer and it looks like if I use 50 - 55# of pressure I should get all the capacity I need. (in the neighborhood of 2,335-2,360# per tire).

I also read that if I go above 60# I may blow out my valve stems. I think I will run at 50, maybe 55#. The stiffer sidewalls should make a nice difference.

Be careful what you read on forums, especially RV ones. You're not going to blow out a valve stem by airing up to 60 lbs, or even 120 lbs, nor will your factory OEM wheel grenade. The pressure rating of your OEM wheel, if it even has one, will be more than the pressure any tire requires that will physically fit on it along with a substantial margin for safety/ error. Don't inflict yourself with a case of Rv board OCD.

I usually ignore idiots of this sort, but the OP and anyone else interested in uprating tires would do well to educate themselves as to the facts about wheel pressure and load ratings.

I'll have no further comment, life's too short to debate with people who are willfully ignorant and choose to provide dangerous advice.