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 > "LT" tire pressures on Expedition

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CapriRacer

Somewhere in the US

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Posted: 04/09/19 11:10am Link  |  Quote  |  Print  |  Notify Moderator

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

Visit my web site: www.BarrysTireTech.com

Ralph Cramden

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Posted: 04/09/19 11:31am Link  |  Quote  |  Print  |  Notify Moderator

.

* This post was edited 04/21/19 12:02pm by Ralph Cramden *

dodge guy

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Posted: 04/09/19 01:13pm Link  |  Quote  |  Print  |  Notify Moderator

“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.


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BenK

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Posted: 04/09/19 01:46pm Link  |  Quote  |  Print  |  Notify Moderator

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...


-Ben Picture of my rig
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Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
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ghostrider421

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Posted: 04/09/19 04:50pm Link  |  Quote  |  Print  |  Notify Moderator

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


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Grit dog

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Posted: 04/09/19 09:59pm Link  |  Quote  |  Print  |  Notify Moderator

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


"Yes Sir, Oct 10 1888, Those poor school children froze to death in their tracks. They did not even find them until Spring. Especially hard hit were the ones who had to trek uphill to school both ways, with no shoes." -Bert A.

CALandLIN

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Posted: 04/09/19 10:57pm Link  |  Quote  |  Print  |  Notify Moderator

Rustycamperpants wrote:

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...


To double check the installers figures you have to use the load capacity the OE tires provided at vehicle manufacturer recommended inflation pressures. Then find the chart for the replacement tires and compare the load capacity they are providing at the installers recommended inflation pressures. Industry standards require a minimum load capacity equal to what the OE tires were providing.

Ralph Cramden

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Posted: 04/10/19 04:24am Link  |  Quote  |  Print  |  Notify Moderator

.

* This post was edited 04/21/19 12:01pm by Ralph Cramden *

Grit dog

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Posted: 04/10/19 09:38am Link  |  Quote  |  Print  |  Notify Moderator

You’re spot on Ralph! Lol at the flubber tire.
If it makes you feel better there are still some PEs with common sense.

We re-engineered a design build project last year, replacing the prescribed 2 - bridges and temporary detour with one precast concrete arch structure and no detour construction. Saved about $4M. Without all 3 parties having common sense, owner, designer, contractor, it would have never happened and often doesn’t.
When I have a good designer that listens, we tend to make money. When I have a bookworm designer, we tend to burn money like it’s free!

Grit dog

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Posted: 04/10/19 09:41am Link  |  Quote  |  Print  |  Notify Moderator

So based on the discussion this far, there is a reason for yellow door stickers, min tire psi etc. and it’s fine. It cannot be expected that more than a certain % of the population want or can analyze things or even recognize hazards.
Hence the no bath tub sticker on your wife’s hair dryer and the no fingers sticker on your lawnmower.
The point is, if one knows wtf they are doing, they can get more out of their machines and their life.

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