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Old 07-26-2014, 02:59 PM   #1
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Default LT Tire pressure

A question for those with HD payload and LT tires. What pressure are you running? My 2012 came with LT245/75/R17 Load Range E. Max inflation from the sidewall is 80PSI.

The truck is my daily driver (25 mile per day, largely highway) and hauls our 5'r. It sees about 35% of it's miles when towing.

Door sticker suggest 55 on front and 60 on rear. Earlier in the season I had aired them up to 70 all round. That seemed to do well, especially considering I had some longer trips to run with the 5'r. Last weekend I dropped them back to 55/60 and this past week I noticed a drop in MPG, about 1.5 over my normal commute. Not a huge deal, but hey fuel is expensive...

So, what is everyone running with similar setups?
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Old 07-26-2014, 05:49 PM   #2
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I have Michelin XLT AT 20's on mine and was running 50F/60R in mine and getting about 16.9 mpg commuting to/from work. Now, I have then 65F/70R and am getting 17.5mpg commuting to/from work. Little rougher ride but hey it's just me and it is a truck. 70F/80R when hauling the 5er.
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Old 07-26-2014, 05:56 PM   #3
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HD payload and stock tires. I keep it at 60lbs for commuting in all 4 tires. Hard to say, but I think it's about 1 more mpg than when I kept 50 lbs in all 4. It all added up and those 10 more lbs does not effect the ride at all. I check the tires every 30 to 60 days.
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Old 07-26-2014, 06:55 PM   #4
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I'm going to run 70 all round for a week and see how it goes. I'll air up to 80 when pulling the 5'r in the rear.
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Old 07-26-2014, 07:42 PM   #5
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Per the door sticker, (55/60 psi) 80 is overinflation but I'd just worry about traction on gravel or wet pavement. I've always run mine at 55/60 and a recent 3,000 mi trip yielded 19 real MPG.
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Old 07-26-2014, 08:06 PM   #6
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60 psi hauling and daily
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Old 07-26-2014, 08:49 PM   #7
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On the first trip pulling our 5er I ran them at 63 and 68. Going to a rally next weekend I'm going to run them at 70 and 75. Still experimenting.
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Old 07-26-2014, 09:55 PM   #8
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Quote:
Originally Posted by ecobeest View Post
My 2012 came with LT245/75/R17 Load Range E. Max inflation from the sidewall is 80PSI.
TRA = Tire and Rim Assn. That's a bunch of engineers hired by the auto and tire industries to test and publish the results of their tests as to proper tire inflation for the load on the tire.

Ignore what Jim and Susie are running, and go by the TRA load/inflation table for your size tire. That means you must weigh the wet and loaded rig on a CAT scale to get the weights on the front and rear axles of the truck. Then weigh it again when not towing and get the weights on the front and rear axles of the truck.

Divide the weight on the axles by 2 to get the approximate weight on each tire. Then apply the load inflation table, using the PSI for the next higher weight.

The TRA tables are hard to find for cars and light trucks. Most tire manufacturers now just say to go by the vehicle manufacturer's weight limits. But if you look hard enough, you can find the TRA tables. Here's one source:
http://toyotires.com/sites/default/f...-LT_102913.pdf

Scroll down to page 23 of 28 and look for LT245/75R17E on single axles (not duals). That's page A12 of the full document, but Toyo didn't publish the whole document.

Here's what you'll find as the load/inflation table for that size tire:

LT245/75R17
PSI . max weight
__ . ___________
35 . 1770 pounds
40 . 1945
45 . 2110
50 . 2270 (max for load range C)
55 . 2430
60 . 2595
65 . 2775 (max for load range D)
70 . 2900
75 . 3050
80 . 3195 (max for load range E)

Example:
Your truck weighs 3300 pounds on the front axle and 4680 on the rear axle. So that's 1,650 on each front tire and 2340 on each rear tire. So for that load, you need 35 PSI in the front tires and 55 PSI in the rear tires. If I had those weights, I'd probably add 5 PSI and make it 40 front/60 rear. More PSI than that and you'll wear out the center of the tire tread prematurely, plus have a harsher ride with no benefit to the higher PSI.


Apply the same logic to the unloaded weights of your truck. Don't go below 35 PSI, but there's no need for more PSI than the TRA table calls for.

As you can see, Ford put plenty of tire weight capacity on the F-150s with HD Payload package. The GVW for the above example is 7,980 and the GVWR of the F-150 with HD payload pkg is 8,200. And the above example is a real-world 2012 F-150 EcoBoost SuperCrew 4x2 towing an 8,000-pound fifth wheel RV.
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Last edited by smokeywren; 07-26-2014 at 10:08 PM.
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Old 07-27-2014, 10:21 AM   #9
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Here's my suggestion:

1 Drive to a flat area. This can be your driveway or the street in front of your house. Just make sure there aren't a lot of cracks, bumps or pot holes in the ground.
2 Draw a thick, straight line across the width of the tire.
3 Drive the car forward at least one-full car length.
4 Inspect the chalk on the ground and on the tire. A tire with the proper air pressure should press the chalk line evenly across the ground. This means you'll see the entire chalk line imprinted on the ground. An over-inflated tire will bulge and only the center of the line will touch the ground. You'll only see a small portion of line if this is the case. If you're tire is under inflated, you'll see only the sides of the lines since the middle of the tire is not making contact with the ground.
5 Adjust your tire's air pressure according to the chalk test results.
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Old 07-27-2014, 03:26 PM   #10
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Quote:
Originally Posted by Norotso View Post
5 Adjust your tire's air pressure according to the chalk test results.

Yep, that's the way we had to do it way back when. That will get you within the ballpark of the correct inflation for the load. But the TRA load/inflation tables makes it much easier and more accurate.
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Old 07-27-2014, 03:26 PM
 
 
 
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