My thinking on this is that the Cooper rep I spoke with is told to recommend this so they are covered for liability reasons. I wasn't paying attention at the beginning of the phone message, but the call was probably taped.
And I know it shouldn't matter, but it wasn't a guy that I was talking to. And I know its wrong, but whenever a woman picks up the line when I make a call like that this my confidence goes way down. I'm thinking about calling tomorrow and trying for someone else.

 

I doubt it is for liability as it could cause much greater harm than you think. Suppose the recommended pressure was 50, and you put on a set of P series tires, with a max pressure of 44. There is a possibility of having a blowout while putting air in the tire, while you are right next to it. Definite good chance of injury.
I am glad you are using some common sense and ignoring what they said.

 

Like I said earlier, this isn't the first time I've run an E rated tire on a 4X4. Its just the first time I've been told (now twice) by someone that should know that I can have 33 psi and be safe. All I had to do was look at them and see something was wrong.
Despite that they are a very smooth and quiet tire. I wouldn't hesitate to by another set again.

After I give the Cooper reps one more chance I might call another manufacturer to see what they say. I'll be sure to post what I hear.

 

Oh my god no one has a clue about this... Ford Determines your proper tire pressure no matter what tire you are running... they test and come up with the tire pressure that is best suited for your truck... The number on the sidewall is only the Max that tire can hold it has nothing to do with what it should have in it... just do not exceed that number... here is the explination from tirerack...

Maximum Inflation Pressure

A tire's maximum inflation pressure is the highest "cold" inflation pressure that the tire is designed to contain. However the tire's maximum inflation pressure should only be used when called for on the vehicle's tire placard or in the vehicle's owners manual. It is also important to remember that the vehicle's recommended tire inflation pressure is always to be measured and set when the tire is "cold." Cold conditions are defined as early in the morning before the day's ambient temperature, sun's radiant heat or the heat generated while driving have caused the tire pressure to temporarily increase.

For the reasons indicated above, It is also normal to experience "hot" tire pressures that are up to 5 to 6 psi above the tire's recommended "cold" pressure during the day if the vehicle is parked in the sun or has been extensively driven. Therefore, if the vehicle's recommended "cold" inflation pressures correspond with the tire's maximum inflation pressure, it will often appear that too much tire pressure is present. However, this extra "hot" tire pressure is temporary and should NOT be bled off to return the tire pressure to within the maximum inflation pressure value branded on the tire. If the "cold" tire pressure was correctly set initially, the temporary "hot" tire pressure will have returned to the tire's maximum inflation pressure when next measured in "cold" conditions.

A tire's "maximum inflation pressure" may be different that the assigned tire pressure used to rate the tire's "maximum load." For example, while a P-metric sized standard load tire's maximum load is rated at 35 psi, many P-metric sized standard load performance and touring tires are designed to contain up to 44 psi (and are branded on their sidewalls accordingly). This additional range of inflation pressure (in this case, between 36 and 44 psi) has been provided to accommodate any unique handling, high speed and/or rolling resistance requirements determined by the tire and vehicle manufacturers. These unique tire pressures will be identified on the vehicle placard in the vehicle's owner's manual.

The tire's maximum inflation pressure is indicated in relatively small-sized print branded near the tire's bead (adjacent to the wheel) indicating the appropriate value. Because tires are global products, their maximum inflation pressure is branded on the tire in kilopascals (kPa) and pounds per square inch (psi). These values can also be found in the industry's tire load & inflation charts.

 

I have read absolutely everything ever written by everybody who what's every discussed tire pressure on the I tire World Wide Web and nobody has answered the question that most people are asking. Okay I'm exaggerating but wow how hard is it to get a straight answer from the manufactures? Thank god for you guys who are probably not experts but at least have tried different pressures and have an opinion as to what is safe. I wrote Hankook tonight the following to see what they have to say.

I have a 2013 F150 XLT Super crew with a 5.5 ft bed. The tires from the factory failed 3 times in 8 months driving on gravel roads. I bought a set of Dynapro ATM P275/65R18 and so far I love them. The question that most of us are asking is " what is the minimum tire pressure"? The max is easy you put it right on the sidewall. The factory pressure is for a completely different tire and I'm sure 35 PSI is too low for this tire.. Sidewalls flex too much, heat builds up to much and the outside treads wears out much quicker than the inside. I realize that there is not a single pressure that works for every situation (i.e. load) but there is a minimum pressure for every tire regardless of load and that's what we want to know.

 

Old thread but everyone keeps asking the same questions. Most of the newer P rated tires in the 20" size are 44 psi max on the sidewall. I've been running 36 to 38 psi cold for everyday use. Best compromise for ride and fuel mileage. This is in regard to my P rated Toyo's...weight of the truck and any suspension changes will have an effect also on the tires "sweet" spot. Minimum psi for a P rated truck tire unloaded would be 34 to 35 psi...for an LT tire 40 psi would be the minimum..these are just my opinions and the pressures I've used in my trucks over the last 40+ years.

 

Thank you PawPaw. Actually 45 PSI is what I've chosen to try for awhile and see how they wear.

 

What is the max pressure stamped on the sidewall?

 

80 psi

 

And you say those are P rated tires and not LT ?

 

No I didn't say either but they are LT

 

So this is what I got back from Hankook:

Hi Michael Murphy,

Tire pressure is tied to the load it is hauling. If a tire has nothing loaded on it, it can have zero air. 35 PSI would be the proper air pressure for a 2013 Ford F150 XLT with P275/65R18 on it.

Best regards,

I don't know but the tire looks low at 35 PSI to me.

 

What exact tires to you have now? I thought I saw Hankook Dynapro P275x65x18 or maybe I misunderstood.

 

No you are correct PawPaw. And this reply was from Hankook. I'm going to run at 45 for awhile but at 35 the tires "felt" good just don't look good.

 

Those are load range "E" LT tires, and I would run them at 50.