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Old 08-03-2015, 08:09 PM   #1
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Tire pressure on 10 ply LT rated?

I recently upgraded my P series tires with a max inflation of 55psi to Toyo LT tires with a max inflation of 80psi. Now when towing I run at max PSI and even with my heavy TT the F150 tows very steady. Unladen however it's quite a bit more bouncy than with the old P tires. What inflation do folks typically run on these tires when not towing? How bout inflation for best MPG? 80 psi doesnt seem to be the best for mileage either.

My mileage kind of tanked with the tire swap, easily 2mpg overall lost when not towing. Seems about the same towing.

IIRC the tire shop initially inflated to 55psi but I could see some roll marks on the tires from cornering.

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Old 08-03-2015, 08:22 PM   #2
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Your mpg prob went down because they are heavier tires. When not towing, I run my d rated at 45 and 60 when towing.

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Old 08-03-2015, 09:20 PM   #3
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You shouldn't run E rated tires at 80psi on a 1/2 ton. You only need what the tire needs for the load. When I ran E tires on my 2010 F150, Discount Tire said 45psi was all that's needed to handle the F150 RAWR of 4050 lbs. I ran them at 35 psi when empty. Ride suffered some but not bad. Running those tires at 80psi on a light weight truck will wear the centers out prematurely. You need to look up the inflation tables for your specific tire and use those numbers. There's a reason why 3/4 ton trucks have two different psi ratings. One is for a load and the other is running empty. You door placard should tell you the empty psi for your truck. JMO but I wouldn't run any more than 50psi in the tires when towing. Also chance are your stock rims aren't even rated for 80 psi.

FWIW my 2500 says 80 psi for max load. That's 6200lbs on the RAWR. Why would you need 80 psi for a lighter load of 4000lbs? Just saying. Adjust your psi accordingly.
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Old 08-03-2015, 11:18 PM   #4
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I found the Toyo specs and they show I should be in that 50psi range. I do however find the truck feels alot more stable with the tires aired up to max. I tow with right close to 4000 on the rear axle in an area known for pretty stout side winds. Next go round I'll try the 50psi in the gorge and see how it goes. The truck will sure ride smoother at lower pressures. I had no idea they posted inflation tables for loads. Thanks for that info. I guess I learn something new every now and then.
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2014 F150 Supercrew 4x4 3.5L EB 3:31 axle
1999 F350 Supercab V10 4x4 3.73 LS
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Old 08-04-2015, 12:14 AM   #5
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I will be heading through the Gorge on Friday. Going to be spending 11 days in NE Oregon. I get to test out my new Equalizer hitch. I kind of hope there is some good wind when I travel through just to see how the hitch does compared to the old Eazlift.

As far as your tires go, if your more comfortable at max psi, then run it there. Just remember that they won't wear as good. But it was mentioned earlier, make sure your wheels are rated to handle 80 psi.

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Old 08-04-2015, 02:36 AM   #6
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P tires and LT tires are two different animals. Toyo actually has an excellent article on determining air pressures between different types of tires, including when you change out the original equipment P tires to a LT tire.

Please note their warning on page 11 (copied below), and how LT tires require higher psi to carry the equivalent load of a P tire.


WARNING! Please note that size for size, LT metric tires require higher air pressures to carry equivalent loads of P-metric tires and that any failure to adjust air pressure to achieve the vehicle’s load requirements will result in tire fatigue and eventual tire failure due to excessive heat build up. Due to the higher PSI requirements of LT metric tires they may not be suitable for replacing O.E. P-metric tires because of the ride harshness that results from higher PSI requirements.
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Old 08-04-2015, 04:12 AM   #7
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While your tires will be rated for more weight check to see if your rims can carry the same.
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Old 08-04-2015, 05:46 AM   #8
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Good info from Toyo Tires Thanks Wmtire
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Old 08-04-2015, 08:37 AM   #9
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The truck in my signature came from the factory with E rated tires. The door sticker says to run 55 in the front and 60 in the rear.
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Old 08-04-2015, 09:23 AM   #10
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I will give a copy of text I used for different fora and topics, and saved so I dont have to write it again and again.
For you the weights must be determined as accurate a possible for the 2 situations , towing and not towing. These weights are the most tricky parts in determining the needed pressure. But If you only give the tires specifications I can also make a Pressure/loadcapacity list for them with use of my extra save formula , the american lists lead to to much loadcapacity for the pressure.

Tirepressure advice is all about load on tire and speed ( and sometimes about alighnment - camber angle).

So if you can give details of car and tires , I can calculate an advice pressure with some reserve for things like, pressure-loss in time, unequall loading R/L, incidental extra load, misreadings of pressure scales,and misyudging of weight, etc.

This is from tires next and can be read from sidewall:
Maximum load or loadindex.
Kind of tire to determine the AT-pressure/pressure needed for the maximum load up to maximum speed of tire, or if lower 160km/99m/h/reference-pressure, wich is not the maximum pressure of tire.
Maximum speed of tire, most given as letter ( Q=160km/99m/h,N=140km/86m/h fi)

If you have offroad or tires looking like that , with large profile blocs that cover a part of sidewall, also mention, they are allowed lesser deflection then a normal road tire, then the tire maker used to determine the maximum load (to my conclusion the case for the Bridgestone tires on Ford Explorer in the Ford/Firestone affaire).

If you cant find all of it give sises of tire and Loadkind, then I will google for it.

From car next and mostly can be found on same plate as the original pressure advices:
GAWR and GVWR ( Gross Axle/Vehicle Weight Rating)
But best would be to determine the real weights in your use on seperate tires or estimate it as acurate as possible, by weighing per wheel(pair) or axle.
Maximum speed , you dont go over for even a minute in your use, eventually different for different situations, for instance when towing or fully loaded.

This apart from trafic regulations, if you drive faster then allowed give that speed. Nature punnisches with tire-failure, police only with a penalty.

Give all that and I will calculate and give a picture of one of my filled in spreadsheets in my answer.

If other then original tires, indead as is already answered other advice is needed, a stiffer tire ( fi C-load instead of P-tire) needs a higher pressure for the same load, or the other way around, has lower loadcapacity for the same pressure.

Greatings from a Dutch pigheaded self-declared tire-pressure-specialist.

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pressure, tire

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