Tire Pressure - Ford Powerstroke Diesel Forum
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post #1 of 5 Old 10-07-2009, 09:33 AM Thread Starter
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Tire Pressure

Anyone know how to figure out exactly what tire pressure you should be using when you are using larger than factory spec tires?

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post #2 of 5 Old 10-07-2009, 01:32 PM
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i usually start at the psi on the side of the tire and adjust if the tires start wearing uneven

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post #3 of 5 Old 10-07-2009, 02:44 PM
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theres a good link on here somewhere that shows you how to determine if you have the right tp. Basically you draw a chalk line across your tire and drive about 20 feet, check where the chalk line wore. If it wore on the outside then your tire is underinflated, if it wears in the middle then they are over inflated, I think you just want to have a happy medium

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post #4 of 5 Old 10-07-2009, 05:40 PM
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post #5 of 5 Old 10-17-2009, 05:08 PM
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Its a percentage of the load. My Factory size is 265/75R16E. The tire is rated at 3415lbs @ 80 psi. I currently run 285/75R16D at 55 psi. The way i figured it is divide your Gross axle weight by 2 to get the load for on tire then divide that into the max load to get the percentage of that then multiple that number by the max psi for the tire. Here is my break down. Also here is the pressure if you have the 5200lb axle.
Front: 4800/2=2400lbs 2400/3305=.73 .73x65=48psi
Rear: 6000/2=3000lbs 3000/3305=.90 .90x65=55psi
Front: 5200/2=2600lbs 2600/3305=.79 .79x65=52psi
I run all my tires at about 50psi. If you know your empty weight front and rear you can reduce by more pressure. All manufactures spec their vehicles to run fully loaded its just easier than give an empty and loaded pressure because if you forget to inflate them before you load you will destroy the tires. Hope that helps.
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