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#4485006 - 08/10/17 06:41 PM Proper inflation pressure?
buck91 Offline


Registered: 04/17/12
Posts: 2449
Loc: West Michigan
So help me decide the proper pressure here. Last year I switched to LT285/70r17 (Load E) tires on my F150 which originally came with P-metrics. Discount Tire has the pressure on the invoice spec'd at 44psi and I have been running that for the past 6k miles. Tread wear looks pretty good, a little bit of should wear up front but I think thats from some hot freeway ramps.

Anyways, factory door sticker lists:
GAWR front 3750lbs
GAWR rear 3850lbs
Tires 235/75r17 108S (load rating) 38psi

I switched to Falken AT3W tires in LT285/70r17 Load E (121/123) with the load table attached in the pic below. If I am reading this correctly, at 35psi these tires will still be exceeding my factory load requirements. Therefore, 35psi would be the proper inflationary pressure (since LT tires aren't rated to run below 35psi)?


_________________________
2011 F150 4x4 5.0L
1996 Mustang GT 5spd/ragtop

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#4485012 - 08/10/17 06:44 PM Re: Proper inflation pressure? [Re: buck91]
4WD Offline


Registered: 09/21/10
Posts: 6390
Loc: Texas
At 40 psi would they still carry all the truck will?

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#4485024 - 08/10/17 06:53 PM Re: Proper inflation pressure? [Re: 4WD]
buck91 Offline


Registered: 04/17/12
Posts: 2449
Loc: West Michigan
Well, at 35psi they are rated at about 2100lbs per tire or 4200lbs per axle... which is greater than the GAWR on either end.
_________________________
2011 F150 4x4 5.0L
1996 Mustang GT 5spd/ragtop

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#4485039 - 08/10/17 07:02 PM Re: Proper inflation pressure? [Re: buck91]
4WD Offline


Registered: 09/21/10
Posts: 6390
Loc: Texas
Might try 40 - I've run a number of 285's over the years and they can wear in the center ...


Edited by 4WD (08/10/17 07:03 PM)

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#4485044 - 08/10/17 07:09 PM Re: Proper inflation pressure? [Re: buck91]
Blkstanger Offline


Registered: 08/13/11
Posts: 1948
Loc: Lakeside, CA
40psi would be a good place to start. See how they wear and feel on the road.
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#4485052 - 08/10/17 07:13 PM Re: Proper inflation pressure? [Re: buck91]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
I think anywhere between 35-40 will be great.

Might get .1% better gas mileage at 40.
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#4485055 - 08/10/17 07:14 PM Re: Proper inflation pressure? [Re: 4WD]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
Originally Posted By: 4WD
Might try 40 - I've run a number of 285's over the years and they can wear in the center ...


Interesting?!!

I would not consider 40 to be "over-inflated" at all?!?
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#4485059 - 08/10/17 07:16 PM Re: Proper inflation pressure? [Re: buck91]
fdcg27 Online   content


Registered: 09/25/09
Posts: 15702
Loc: OH
Curious as to why you'd put LTs on a half ton intended for P tires.
Harsher ride for sure but probably longer life.
To get that longer life you probably need to run the higher pressures that these tires typically call for in those applications where they are OEM.
What does Ford, not some universal tire guide, recommend for the F250 and F350 that would come with LT tires?
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#4485062 - 08/10/17 07:16 PM Re: Proper inflation pressure? [Re: buck91]
bubbatime Offline


Registered: 03/18/08
Posts: 5627
Loc: South Florida
35 PSI is dangerously low, and is endangering you and others on the road. They run dangerously hot at lower pressures. Most info I've seen is that you need to run them AT LEAST 50-55 pounds to stay on the safe side.

Load range E tires on a 2011 F150? Not sure why you chose those tires. I would have definitely went a different direction.


https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&ved=0ahUKEwjl3ayK8c3VAhWHVyYKHWjECcUQFghgMAc&url=http%3A%2F%2Fwww.toyotires.ca%2Fsites%2Fdefault%2Ffiles%2Fimce%2FReplacing%2520Tires%2520on%2520Light%2520Trucks.pdf&usg=AFQjCNFQnGyQPgK6hseaI9fyYTOVoQKxzg

http://www.barrystiretech.com/pmetricvsltmetric.html

http://www.tirereview.com/tire-types-and-load-capacity/

And this table from discount tire is EXCELLENT. Scroll down to load range E.

https://forum.ih8mud.com/attachments/discount-tire-load-inflation-tables-pdf.394359/
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#4485090 - 08/10/17 07:54 PM Re: Proper inflation pressure? [Re: buck91]
CapriRacer Online   content


Registered: 02/22/03
Posts: 3370
Loc: Somewhere in the US
Originally Posted By: buck91
So help me decide the proper pressure here. Last year I switched to LT285/70r17 (Load E) tires on my F150 which originally came with P-metrics. Discount Tire has the pressure on the invoice spec'd at 44psi and I have been running that for the past 6k miles. Tread wear looks pretty good, a little bit of should wear up front but I think thats from some hot freeway ramps.

Anyways, factory door sticker lists:
GAWR front 3750lbs
GAWR rear 3850lbs
Tires 235/75r17 108S (load rating) 38psi

I switched to Falken AT3W tires in LT285/70r17 Load E (121/123) with the load table attached in the pic below. If I am reading this correctly, at 35psi these tires will still be exceeding my factory load requirements. Therefore, 35psi would be the proper inflationary pressure (since LT tires aren't rated to run below 35psi)?

[image deleted]


The proper way to do this is to match the load carrying capacity.

But first, let's check a few things: According to Tire Guides - a publication that catalogs what the vehicle tire placards say 9and a few other things), a 2011 ford F-150 4X4 with P235/75R17 108S's takes 35 psi (the 38 psi doesn't make sense to me, but 35 psi does, so please check that!) I'm going to assume there was a reading error made, so I'm going with 35 psi.

At 35 psi a P235/75R17 108S carries 2205 #, but since it is on a pickup, it needs to be derated by 1.1 = 2005#.

In order to carry the same load, an LT285/70R17 needs to use [drumroll] ...... well, less than 35 psi. And since I think 35 psi is the lowest pressure an LT tire should use, 35 psi is what I think this the right answer (plus, it's the same as the placard, so the spring rates will be very close.
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Visit my web site: www.BarrysTireTech.com

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#4485237 - 08/10/17 10:58 PM Re: Proper inflation pressure? [Re: buck91]
OVERKILL Offline


Registered: 04/28/08
Posts: 36464
Loc: Ontario, Canada
This might help:



Which was from This thread.

Basically the same question you had, and the OP there was asking for somebody who had the C-spec LT tire equipped F-150 to post their placard, which is what I've copied above.
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#4485291 - 08/11/17 12:28 AM Re: Proper inflation pressure? [Re: buck91]
buck91 Offline


Registered: 04/17/12
Posts: 2449
Loc: West Michigan
Thank you overkill, that is very helpful. No, 38psi is not an error. I still believe if I am reading the load chart correctly that 35psi on the LT's would be good but I will try the oe spec of 40 for a while first.
_________________________
2011 F150 4x4 5.0L
1996 Mustang GT 5spd/ragtop

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#4485394 - 08/11/17 07:23 AM Re: Proper inflation pressure? [Re: bubbatime]
zeng Offline


Registered: 09/01/15
Posts: 2188
Loc: Malaysia
Originally Posted By: buck91
So help me decide the proper pressure here. Last year I switched to LT285/70r17 (Load E) tires on my F150 which originally came with P-metrics. Discount Tire has the pressure on the invoice spec'd at 44psi and I have been running that for the past 6k miles. Tread wear looks pretty good, a little bit of should wear up front but I think thats from some hot freeway ramps.

Anyways, factory door sticker lists:
GAWR front 3750lbs
GAWR rear 3850lbs
Tires 235/75r17 108S (load rating) 38psi

I switched to Falken AT3W tires in LT285/70r17 Load E (121/123) with the load table attached in the pic below. If I am reading this correctly, at 35psi these tires will still be exceeding my factory load requirements. Therefore, 35psi would be the proper inflationary pressure (since LT tires aren't rated to run below 35psi)?



This appears logical, BUT this chart disregards tire load index 121 and tire load range E being tire properties .....
in this context , tire pressure recommendation of 35 psi is anappropriate.


Originally Posted By: bubbatime
And this table from discount tire is EXCELLENT. Scroll down to load range E.
https://forum.ih8mud.com/attachments/discount-tire-load-inflation-tables-pdf.394359/


According to this Tire Discount chart having regards of Load Index 121 and load range E, the proper pressure shall be about 42 psi minimum ..... the 44 psi recommended is appropriate as it is above Minimum 42 psi.
40 psi in under-inflation!

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#4485573 - 08/11/17 10:15 AM Re: Proper inflation pressure? [Re: zeng]
CapriRacer Online   content


Registered: 02/22/03
Posts: 3370
Loc: Somewhere in the US
Originally Posted By: zeng
....... According to this Tire Discount chart having regards of Load Index 121 and load range E, the proper pressure shall be about 42 psi minimum ..... the 44 psi recommended is appropriate as it is above Minimum 42 psi.
40 psi in under-inflation!


There is something very strange about those charts.

Load carrying capacity varies by size and inflation pressure, but NOT by Load Range. So there shouldn't be separate charts for the different Load Ranges. I don't know where they came up with those charts, but I have never seen load carrying capacity expressed in that way - and I suspect it is wrong.
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Visit my web site: www.BarrysTireTech.com

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#4485920 - 08/11/17 05:01 PM Re: Proper inflation pressure? [Re: buck91]
userfriendly Offline


Registered: 06/03/03
Posts: 2630
Loc: LaFinDuMonde
I use that size and 285/75/16s on 1500 & 3500 pickup trucks all the time. Preferably on 9 inch wide wheels so the centers don't wear. Ten inch wide would be better yet. Inflation on the 1500s is 35psi and 50 to 65psi on the HDs depending on the load.
The last set of 285/75/16s came off a taco Tacoma, I traded a 6.5x55 Tikka for. They went on an 06 3500 Dmax, 16X8" wheels.
Later, 285/70/17 Duratrac on 17X9" steel pro-comp wheels went on that truck @ 65psi.

People clue challenged about off-road ask the same question on every thread that mentions LT tires on half ton trucks;
"Why did you do that?" Typically by the same members who posted the same question 50 x already.

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