Tire pressure
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Cross-Country
Joined: Oct 2008
Posts: 61
Likes: 4
Tire pressure
I have 315/70/17 D load range BFG A/T's on my 99.5' V10 ext. Cab F250.
I'm running them at 40psi right now. Admittedly, I've never owned a vehicle this heavy. I Don't tow or haul anything heavy.
What do you gun think I should be running in my tires.
I'm running them at 40psi right now. Admittedly, I've never owned a vehicle this heavy. I Don't tow or haul anything heavy.
What do you gun think I should be running in my tires.
Hotshot
Joined: Aug 2006
Posts: 17,400
Likes: 319
From: Whittier, CA
First of all, I am honor bound to tell you that you should have load range E tires on your Superduty.
Your load range D tires may have a load rating equal to, or even higher than a stock 17"-E tire. Lets assume that they do, and they are 3,195#. But the LR-E tire does that at 80 PSI and the LR-D tire does that at 65 PSI. Some quick math can tell you what pressure to run.
Your door pillar has the recommended inflation for the stock 17" tire. Lets say it is 70# out of the tire maximum rating of 80#. You would then be running the tire at 7/8 of maximum, which is a factor of 0.88.
Then some simple math can tell us what pressure to run on a 65 PSI rated tire to carry the same load as the 80 PSI tire. The formula would be 65 * 0.88 = 57.2. Thus, to equal the capacity of the stock tire, run the LR-D tire at 57 PSI.
I'm making a lot of assumptions in the above, so change the values to suit your truck and your tire. Change the values in the formula to fit your equipment. Hopefully you get the idea.
Or you could forget all that math and do the "chalk test". Google it. But personally I don't think the chalk test offers much help with stiff highway or all-terrain tires.
Your load range D tires may have a load rating equal to, or even higher than a stock 17"-E tire. Lets assume that they do, and they are 3,195#. But the LR-E tire does that at 80 PSI and the LR-D tire does that at 65 PSI. Some quick math can tell you what pressure to run.
Your door pillar has the recommended inflation for the stock 17" tire. Lets say it is 70# out of the tire maximum rating of 80#. You would then be running the tire at 7/8 of maximum, which is a factor of 0.88.
Then some simple math can tell us what pressure to run on a 65 PSI rated tire to carry the same load as the 80 PSI tire. The formula would be 65 * 0.88 = 57.2. Thus, to equal the capacity of the stock tire, run the LR-D tire at 57 PSI.
I'm making a lot of assumptions in the above, so change the values to suit your truck and your tire. Change the values in the formula to fit your equipment. Hopefully you get the idea.
Or you could forget all that math and do the "chalk test". Google it. But personally I don't think the chalk test offers much help with stiff highway or all-terrain tires.
Hotshot
Joined: Aug 2006
Posts: 17,400
Likes: 319
From: Whittier, CA
50 * 0.88 = 44 PSI.
If you are running empty all the time, the 40 you were running before might be about right.
What does your door pillar show? What tire size and what inflation?
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