"LT" tire pressures on Expedition

Ralph Cramden wrote:

Grit dog wrote:
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.

That's a good one.


BTW, did anyone mention nitrogen in this thread? Now off to pump up my tire and see if I can blow the valve stem out of it.

Don't say the N word unless you want 10 pages out of this thread.
BTW I got $20 for anyone who will bite, that you don't blow a valve stem out! Lol

Only time I worry about rim pressure, is when they are those funky 16.5 split rims.

You are re-engineering part of the suspension by changing tire class and size

The door label info is for the tire class and size listed on that label. If changing (re-engineering) the tire class and size, you need to know and understand a bit more

Tires do much more than just carry weight. That ‘squishiness’ mentioned is, IMHO, more to do with how the vehicle engineers designed in ‘ride quality’...not towing metrics

Ask what the ‘new’ tires OEM specifications for wheel rim width range is...vs...what your actual rim width is. Make sure you have the ‘bead to bead’ width, as that is what most OEM tire specifications use

Narrower is more for ‘ride quality’ and the wider is more for ‘handling’ performance. All of my after market wheel rim width is at or a bit wider than tire spec and is the way I like it....ride quality is not on my ‘have to have list’ and is at the bottom of my ‘Nice to have list’

Barry is one of the tire engineers on this forum...listen to him. Some of the other advice is border line dangerous, but the advice on these freebie forums are worth the price paid...

“E” rayed tires are too much for a 1/2 ton. They are unecesaary and heavy. Most it would need are “C” rated tires. Running tires severely under inflated is not good for longevity or handling.

.

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?

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.

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.

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.

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.