Quote:
Originally Posted by ewinghr
The truck weighs 8,000 lbs full of fuel with just me in it.
Right now I'm running them at 70 psi in the front and 66 psi in the rear. Does that sound right?
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No, it sounds like you're way overinflated for unloaded cruising when grossing 8,000 pounds. 70 PSI in the front tires is enough to support about 7,000 pounds on the front axle. Your front axle GAWR is only 5,200 pounds, so I hope you never have over 5,200 pounds on the front axle. For 5,200 pounds front axle weight, the most you'd need in those big tires is 50 PSI.
66 PSI in the rear tires is enough to support over 6,600 pounds on the rear axle. If you have 6,600 pounds on the rear axle, you're going to have a GVW of over 11,000 pounds, or more than a thousand pounds over the GVWR of your truck.
Load/inflation table for LT285/75R16
PSI Max weight
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35 2,130
40 2,340
45 2,540
50 2,755
55 2,925
60 3,110
65 3,305
70 *
75 *
80 *
* = you'll never need that much PSI unless you're severly overloaded. That's why a load range D tire is all you need in size LT285/75R16.
Quote:
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I got the tire inflation chart from BFG, but it makes no sense to me.
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Weigh the truck on a CAT scale to get the weight on each axle. Then divide that axle weight by two to get the approximate weight on each tire. Then apply the above chart.
For example, if your front axle weighs 4,500 and your rear axle weighs 3,500 for a GVW of 8,000 pounds, that's 2,450 pounds on each front tire and 1,750 on each rear tire. The chart above says you need at least 45 PSI to handle 2,450 pounds, and you need at least 35 PSI to handle 1,750. So you would be perfectly safe with 45 front and 35 rear. But if you'd feel more comfortable with a bit more fudge factor, then maybe run then at 50 front and 40 rear when unloaded.
When loaded for bear with a GVW of 10,000 pounds, you'll probably have a front axle weight of less than 5,000 pounds and a rear axle weight of less than 6,000 pounds. So that would be a max of 2,500 pounds on each front tire and 3,000 pounds on each rear tire. For that load, the chart above says you need at least 45 PSI in the front and 55 in each rear tire. So up one notch as a fudge factor, and run 50 front and 60 rear.
IOW, unless you're severely overloaded, you should never need more than 50 front and 60 rear - as long as you have those big tires. Smaller tires have a different load/inflation table. And bigger tires have a different load/inflation table too. So use the correct load/inflation table for your size tires.
