Just bought a set of Cooper Discovery AT3's (275/70/18 E rated). After I got home I thought they looked a little soft. I checked the PSI and they were all at 35. This after drving at highway speeds for a couple hours. I thought that was a little low for an E rated tire. I have run E rated before and never had them lower then 45psi. I called Discount Tire where I just bought them and the salesman told me that the truck called for 35psi and it doesn't matter what the rating is. This dosen't sound right to me. Any opinions?

 

You can run them at 35 PSI and not have any problems if you don't do any hauling/towing etc IMO. I have the STT's (E Rated) and run 40 in mine. It really just comes down to how much towing/hauling you do and personal preference.

 

At this point I'm not towing or hauling anything with any weight so I'm really under utilizing these tires, but 33/35 psi made the tires look low. I'm more worried about uneven wear. I aired them up to 40psi cold and they look better and I didn't really sacrifice any ride quality. Guess I'll stay at that PSI and just keep a watchfull eye on the tread.

 

45 should be your minimum. As far as Discount tire saying for the truck it is 35 no matter what tire, they are idiots. If that were true, why for F150s that come with LR E tires is the recommended 50. Or with LR C 40 or 45. I can never understand how a company that even on their website state running too low is dangerous can have their people come out with such stupid comments.
35 is definitely too low, even for an unloaded F150. The tire does not even have half it's load carrying ability at that pressure, which is far below the GAWR or even unloaded weight of the front axle.

 

I agree with Kingfish 35 psi is way too low on a LT tire.

 

I've always run E rated tires at 45psi or higher. I have them at 40 now. I might give it a coouple weeks and bump them up to 45. If the ride quality doesn't change I'll go with what I've always gone with in the past.
Like I said, it didn't sound right to me.

 

Unless those tires have a max pressure of 65, 40 is still too low. The truck weighs in at around 5400lbs at least, with most of that in the front. At 40, those tires at best handle have their max weight or around 1800 lbs. Which is probably right at what the front of the truck weighs in at. Ad any load or passengers, and you are over that weight.
PS - Vehicle that come with a LR E max 80 psi tires will have their TPMS fault set at 46 psi. Since this is a vehicle that normally does not come with LR E (only the 8200lbs GVWRs do), you have a little leeway, but I would not leave it at 40.

 

I don't have "E"s but the door sticker is only good for the stock tires or equal. I agree that your pressure is too low, look on the tire and it will tell you what the MAX pressure is and stay below that.

Mine have a 44psi max and I run them around 38-40. I always stay under max because heat will raise the pressure if you are running air, nitrogen........I don't know.

 

That's not a completely accurate explanation because the max pressure on the side of the tire is based on a cold (non-opeating) pressure. The manufacturer understands this. In other words, you tire has a max of 44 psi. If you fill it to 44 cold and it raises to 52 hot going down the freeway, that's A-OK. If you're loading a particular tire up to its max weight capability, you need to have it pumped up to that max pressure.

Nitrogen pressure will not vary with temperature. That's the so called 'benefit' of using it, but it's pretty impractical in a daily driven environment. Pretty much a sales gimmick.

 

The MAX PSI on a load range E tire is 80. I'm certainly not running these tires just below that. No need. Even when i drove an F350 I ran those tires at around 55 unless I was towing a 8000lb boat. And at 55 psi the truck rode like a tank. I'm going to play with these tire on the F150, but will probably settle with 45. That is the PSI I have been running for the last 20K miles on the Goodyear Silent Armours, and they look like they are new.

 

I forget that alot of people drive their truck around empty, I use mine for work. It always has about 500 lbs in it minimum, so that is why my tires are just under the max pressure. You guys are right, if I was running empty then I'd probably drop my pressure a smidge too. My bad.

Also had a friend that had a warrentee turned down because of over pressuer, his were inflated to max at cold. When they checked them hot he was like 7lbs over.

When I had my 3/4 ton it called for 80 psi too, I ran them at around 65 most of the time but pumped them up for a load.

Anyhoo I still think 35 is way too low, that would probably make them wear on the outside more than the center. I think you are on the right track to air them up a tad......and the tire store guy is wrong. IMHO

 

The max psi on an E tire varies from tire to tire. My E rated Wrangler MT/R-K's are 60.

 

I just put Nitto Terra Grapplers LT 275/70-18 LR E on my truck. Nitto recommended 42psi front and rear when I emailed their tech department. I will use that as my minimum.

 

I run 45 in my Michelin LT265-70/17E's. Truck rides a little firmer but it's an FX4 Screw. I like the road feel

 

Get hold of Cooper and tell them what tire you have and what you have it on and they will give you the proper PSI for your application.
http://us.coopertire.com/Contact-Us.aspx