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Proper inflation pressure? #4485006
08/10/17 06:41 PM
08/10/17 06:41 PM
Joined: Apr 2012
Posts: 2,590
West Michigan
buck91 Offline OP
buck91  Offline OP
Joined: Apr 2012
Posts: 2,590
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
Re: Proper inflation pressure? [Re: buck91] #4485012
08/10/17 06:44 PM
08/10/17 06:44 PM
Joined: Sep 2010
Posts: 7,009
Texas
4WD Offline
4WD  Offline
Joined: Sep 2010
Posts: 7,009
Texas
At 40 psi would they still carry all the truck will?

Re: Proper inflation pressure? [Re: 4WD] #4485024
08/10/17 06:53 PM
08/10/17 06:53 PM
Joined: Apr 2012
Posts: 2,590
West Michigan
buck91 Offline OP
buck91  Offline OP
Joined: Apr 2012
Posts: 2,590
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
Re: Proper inflation pressure? [Re: buck91] #4485039
08/10/17 07:02 PM
08/10/17 07:02 PM
Joined: Sep 2010
Posts: 7,009
Texas
4WD Offline
4WD  Offline
Joined: Sep 2010
Posts: 7,009
Texas
Might try 40 - I've run a number of 285's over the years and they can wear in the center ...

Last edited by 4WD; 08/10/17 07:03 PM.
Re: Proper inflation pressure? [Re: buck91] #4485044
08/10/17 07:09 PM
08/10/17 07:09 PM
Joined: Aug 2011
Posts: 2,026
Lakeside, CA
Blkstanger Offline
Blkstanger  Offline
Joined: Aug 2011
Posts: 2,026
Lakeside, CA
40psi would be a good place to start. See how they wear and feel on the road.


99 Jeep WJ 4.7 190,000 Maxlife 10w30, Fram Ultra.
Re: Proper inflation pressure? [Re: buck91] #4485052
08/10/17 07:13 PM
08/10/17 07:13 PM
Joined: Dec 2016
Posts: 6,262
Waco, TX
Linctex Offline
Linctex  Offline
Joined: Dec 2016
Posts: 6,262
Waco, TX
I think anywhere between 35-40 will be great.

Might get .1% better gas mileage at 40.


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: Proper inflation pressure? [Re: 4WD] #4485055
08/10/17 07:14 PM
08/10/17 07:14 PM
Joined: Dec 2016
Posts: 6,262
Waco, TX
Linctex Offline
Linctex  Offline
Joined: Dec 2016
Posts: 6,262
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?!?


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: Proper inflation pressure? [Re: buck91] #4485059
08/10/17 07:16 PM
08/10/17 07:16 PM
Joined: Sep 2009
Posts: 16,026
OH
fdcg27 Offline
fdcg27  Offline
Joined: Sep 2009
Posts: 16,026
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?


17 Forester 18K VME 0W-20
12 Accord LX 92K PP 5W-20
09 Forester 95K M1HM 10W-30
01 Focus ZX3 118K PP 5W-20
96 Accord LX 104K T5 10W-30
95 318i
Re: Proper inflation pressure? [Re: buck91] #4485062
08/10/17 07:16 PM
08/10/17 07:16 PM
Joined: Mar 2008
Posts: 5,841
South Florida
bubbatime Offline
bubbatime  Offline
Joined: Mar 2008
Posts: 5,841
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/


17 Chrysler Pacifica Mobil 1 5W30
13 Yamaha XT250 Valv MC 10W40
12 Suzuki S40 Rotella 15W40
10 Acura TSX 2.4 PZL Plat 5W30
06 GMC Sierra Nextgen 10W30


Re: Proper inflation pressure? [Re: buck91] #4485090
08/10/17 07:54 PM
08/10/17 07:54 PM
Joined: Feb 2003
Posts: 3,422
Somewhere in the US
CapriRacer Offline
CapriRacer  Offline
Joined: Feb 2003
Posts: 3,422
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.


CapriRacer

Visit my web site: www.BarrysTireTech.com
Re: Proper inflation pressure? [Re: buck91] #4485237
08/10/17 10:58 PM
08/10/17 10:58 PM
Joined: Apr 2008
Posts: 37,187
Ontario, Canada
OVERKILL Offline
OVERKILL  Offline
Joined: Apr 2008
Posts: 37,187
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.


2018 RAM 1500 Big Horn EcoDiesel
2016 Grand Cherokee SRT
Re: Proper inflation pressure? [Re: buck91] #4485291
08/11/17 12:28 AM
08/11/17 12:28 AM
Joined: Apr 2012
Posts: 2,590
West Michigan
buck91 Offline OP
buck91  Offline OP
Joined: Apr 2012
Posts: 2,590
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
Re: Proper inflation pressure? [Re: bubbatime] #4485394
08/11/17 07:23 AM
08/11/17 07:23 AM
Joined: Sep 2015
Posts: 2,260
Malaysia
zeng Offline
zeng  Offline
Joined: Sep 2015
Posts: 2,260
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!

Re: Proper inflation pressure? [Re: zeng] #4485573
08/11/17 10:15 AM
08/11/17 10:15 AM
Joined: Feb 2003
Posts: 3,422
Somewhere in the US
CapriRacer Offline
CapriRacer  Offline
Joined: Feb 2003
Posts: 3,422
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.


CapriRacer

Visit my web site: www.BarrysTireTech.com
Re: Proper inflation pressure? [Re: buck91] #4485920
08/11/17 05:01 PM
08/11/17 05:01 PM
Joined: Jun 2003
Posts: 2,695
BC, Canada
userfriendly Offline
userfriendly  Offline
Joined: Jun 2003
Posts: 2,695
BC, Canada
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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