psi for big tires
Senior User
Joined: Apr 2004
Posts: 245
Likes: 0
From: Homer, Alaska
Here is what I do when I get new tires...
I mark a line of chalk down the entire width of the tire (the part that actually touches the pavement) on all 4 tires, and then drive down the road. Get back out and check to see where the chalk has worn away. If it is wearing off first in the center of the tread, your tire pressure is too high. If it is too low, then the chalk will wear off on the outside of the tires first. You want a uniform wear pattern in the chalk, and at that point you know your tire pressure is optimal.
Of course, you'd want to do it again if you were hauling a heavy load, or if it wasn't far, just remember what PSI your tires are at, add 10-15 and do your haul, then get back to your old PSI.
I mark a line of chalk down the entire width of the tire (the part that actually touches the pavement) on all 4 tires, and then drive down the road. Get back out and check to see where the chalk has worn away. If it is wearing off first in the center of the tread, your tire pressure is too high. If it is too low, then the chalk will wear off on the outside of the tires first. You want a uniform wear pattern in the chalk, and at that point you know your tire pressure is optimal.
Of course, you'd want to do it again if you were hauling a heavy load, or if it wasn't far, just remember what PSI your tires are at, add 10-15 and do your haul, then get back to your old PSI.
Posting Guru
Joined: Nov 2002
Posts: 2,440
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From: Ventura County, CA
Originally Posted by rmartin11
I just put 315 75r 16 under my 02 f350sd. the air pressure was set at the tire dealer at 65 psi, but the tire says max of 50 psi. What do you guys run on your big tires?
Just for curiosity's sake, call the tire dealer and ask them why they set it at 65 instead of the recommended 50psi. Then, if you don't mind, let us know what pearls of wisdom they emparted in so doing. Their logic is mind-baffling!
Thanks,
DS
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Posting Guru
Joined: Feb 2003
Posts: 2,221
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From: Dallas
Originally Posted by cwb
That's a good question. When are you going to ask about the big tires? 
Always a quick one...
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Senior User
Joined: Sep 2003
Posts: 117
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From: Jackson, TN
Originally Posted by rmartin11
I just put 315 75r 16 under my 02 f350sd. the air pressure was set at the tire dealer at 65 psi, but the tire says max of 50 psi. What do you guys run on your big tires?
Elder User
Joined: Feb 2003
Posts: 881
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From: NJ ... the garbage state
I definatly wouldnt air them higher then manufacturers reccomendation. If you go to tire manufacturers website, it will tell you the maximum payload of the tire, and thats at the max psi. If your lighter then that, you can lower the psi a bit to try to improve ride. The chalk method dictates one of the best ways to easily tell how your tires will wear, as opposed to waiting 10,000 miles and seeing what part is wearing out first.
Post Fiend
Joined: Aug 2002
Posts: 5,324
Likes: 1
From: Denton,TX
I do the same thing psdtenn does. I run mine between 40-45 when unloaded and inflate to max when towing or hauling. The tire dealer probably read the pressure from the sticker inside your door jamb instead of looking at the tire. I had some idiot at a quick lube place inflate my rear tires to 80 PSI one time doing the exact same thing. The next time my oil needed to be changed I started doing it myself!
