Tire pressure help

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Hi all, so I have a 2013 F150 and replaced the tires with a set of Cooper Discoverer ATP tires in 275 /70 R18 E Range tire (Since finding bigger tires in anything else is difficult)

I know E range have a different PSI requirement than the typical LT rated tires. I have mine aired up to around 48 PSI. Is that too much for daily driving? Ride does seem a little stiff and it takes bumps hard. I know it will have more feedback than an LT tire. I just want to make sure my tires last a long time!

p.s. Does anyone else have these? Are they a little loud on the road?
 
Originally Posted by Env1ous
Ride does seem a little stiff and it takes bumps hard.


Your answer is right there.

Drop 5 PSI and drive for a week to test.
 
Thanks for the quick reply! Will do. Rather ask people with experience. I looked on forums and got so many different answer. It was making my head spin!
 
Just a reminder; a load range E tire is standard for 3/4 ton trucks. With a 3/4 ton truck tire, it's going to be a a harder ride. Fill to the pressure on the door sticker.
 
Last edited:
Originally Posted by das_peikko
What does it say on the tire for the maximum? I always go 4 PSI below the maximum on the tire.


80PSI max. LOL Not going to 76. Don't need it that high. I just saw the max on it.
 
Originally Posted by gfh77665
Originally Posted by Env1ous
Ride does seem a little stiff and it takes bumps hard.

Your answer is right there.

Drop 5 PSI and drive for a week to test.

Agree....and also watch for any developing wear patterns....center wear = overinflated, edge wear (rear) underinflated. Expect a little edge wear on the fronts...but that'll be taken care of with rotation.
 
IIRC, the "proper" method for determining pressure is to use the load tables.

There's info about this on CapriRacer's site:
http://www.barrystiretech.com/

If you go to the load tables and see that your factory P-rated tires which were, for the sake of this example, 275/60R18s and spec'd 35psi, which results in a load rating of 2,403lbs, we then need to de-rate them by 10% to account for a P-rated tire on a truck/SUV, which results in a 2,185lb rating.

This is actually documented here:
https://www.toyotires.ca/sites/default/files/application_of_load_inflation_tables_20170203.pdf

So, you look at the load table for the LT tires, which is, for your size, down on page 23, and we see that for a 275/70R18 we need 40PSI to achieve roughly the same weight rating.

So, find your factory tires in the P-metric list, find their weight rating, derate them by 10%, and that will give you the the minimum value you need to shoot for when choosing a pressure for the LT tires.
 
Originally Posted by das_peikko
I always go 4 PSI below the maximum on the tire.


Why?
 
Originally Posted by RamFan
Originally Posted by das_peikko
I always go 4 PSI below the maximum on the tire.


Why?

Because that's what he was told by a "reliable source"
smirk2.gif


https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/5057191/tire-pressure

Just ignore him. He's trolling as usual.
 
Originally Posted by OVERKILL
IIRC, the "proper" method for determining pressure is to use the load tables.

There's info about this on CapriRacer's site:
http://www.barrystiretech.com/

If you go to the load tables and see that your factory P-rated tires which were, for the sake of this example, 275/60R18s and spec'd 35psi, which results in a load rating of 2,403lbs, we then need to de-rate them by 10% to account for a P-rated tire on a truck/SUV, which results in a 2,185lb rating.

This is actually documented here:
https://www.toyotires.ca/sites/default/files/application_of_load_inflation_tables_20170203.pdf

So, you look at the load table for the LT tires, which is, for your size, down on page 23, and we see that for a 275/70R18 we need 40PSI to achieve roughly the same weight rating.

So, find your factory tires in the P-metric list, find their weight rating, derate them by 10%, and that will give you the the minimum value you need to shoot for when choosing a pressure for the LT tires.


After looking. It says around 45psi. I think I am currently around 50. So I will decrease and see how 45psi feels and look at tire wear. I saw something called the calk test, to make sure the inflation looks good?
 
Originally Posted by das_peikko
What does it say on the tire for the maximum? I always go 4 PSI below the maximum on the tire.


Didn't you read the post?! They are Load Range E tires which means they have a 80PSI maximum pressure and you are recommending 76PSI?!

When I went to from P to an LT my tire shop (which referenced Toyo's inflation tables) recommended 45PSI front and rear.
 
Originally Posted by JohnnyJohnson
If you want a soft ride don't buy E rated tires.


Don't want a soft ride. But when I hit bumps my rear kicks out on me. So I was more so wondering if I had them over inflated and I do. So it does hit bumps a little stiffer than it should
 
Inflate them to recommended factory pressure if they are the correct tire size and load range. It seems the last set of E range tires on Ford pickup I owned was 51 psi front and 60 psi rear. That was a 1990 F-250 4x4 diesel. Your results may vary...
 
Originally Posted by Env1ous


Don't want a soft ride. But when I hit bumps my rear kicks out on me. So I was more so wondering if I had them over inflated and I do. So it does hit bumps a little stiffer than it should


ALL unloaded trucks do THAT ... ! Put 1000 lbs in the back ... that will fix it ! Or run the rear tires at even lower pressures ... when EMPTY.
 
I wanted to stay with LT tires for my 89 k1500 because that's whats on the door jam and wanted the Cooper AT3's and they only came in E rated or at least that's all my tire shop could get. When I first drove it off the lot I though it was somewhat ruff so when I got home I checked and they had put 50 lbs in them. After a couple thousand miles I decided to drop them down to 45 lbs and what a difference it made so I keep them there, much better on the back. I tried 40 lbs but that made it handle somewhat bad, like the steering was delayed.
 
Originally Posted by JohnnyJohnson
If you want a soft ride don't buy E rated tires.


That's right! Why would you want 3/4 ton truck tires on a 1/2 ton truck? You've already bought them and now you have to try and make it ride like an LT tire. My guess is that the door sticker says 35 psi. Don't go over 40 psi. Running those tires at the maximum pressure printed on the tires is dangerous.
 
Originally Posted by MParr
Originally Posted by JohnnyJohnson
If you want a soft ride don't buy E rated tires.


That's right! Why would you want 3/4 ton truck tires on a 1/2 ton truck? You've already bought them and now you have to try and make it ride like an LT tire. My guess is that the door sticker says 35 psi. Don't go over 40 psi. Running those tires at the maximum pressure printed on the tires is dangerous.


Because they dont have larger sizes in P rated tires. And if they do they are difficult to find. I don't want them to ride like an LT. But my KO2s weren't as rough or didn't kick out like these do. Same PSI so I just wanted to fine tune it
 
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