Unloaded PSI in new tires?

[ewinghr]

I upgraded to the E rated BGR AT/KO that is an 80psi max tire. I run the 80psi when I'm fully loaded, but what should I be running the tire at when unloaded?

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?

I got the tire inflation chart from BFG, but it makes no sense to me.

[JW350]

The tire inflation chart shows you the minimum pressure for a given load. If you have the weight of both your font and rear axles, use those to find the appropriate tire pressure on the chart for the front and rear wheels.

[SmokeyWren]

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?

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
--- ----------
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.

I got the tire inflation chart from BFG, but it makes no sense to me.

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.

[ewinghr]

I run all 4 at 80 psi when I have the truck camper loaded and towing the boat. It just feels more stable and I don't rock side to side down the highway.

I had the Load D range in the same tire and those didn't feel good fully loaded and they wore really fast.

I bet a run a bit over gvw when fully loaded so that might be the reason why.

Am I more at risk of a blowout running over inflated or under inflated?

[SmokeyWren]

Originally Posted by ewinghr

Am I more at risk of a blowout running over inflated or under inflated?

Underinflated for the load can cause a blowout in a heartbeat. By overinflated, if you mean for the load, then the only things bad are the harshess of the ride and the tires will wear out faster in the center of the tread.

If by overinflated you mean over 80 PSI cold, then simply don't do dat.

[chris u]

I run my tires at 47 lbs. during the winter when not towing just less pressure more traction. Run at 65 in the front and 80 in the rear when towing. Just what I do doesn't mean it's right but seams to work.

[Blue Water Runner]

Unloaded I run 55 up front and 60 in the rear. Loaded with the truck camper and boat I run 70 up front and 80 out back.

[TTBadDog]

When I first bought my new to me 03 I inflated the tires to 65. Ride is pretty harsh on the small bumps. I am sort of curious how much difference there is in MPG from 45 to 65 without going through all the hand calculations again. Are we talking 1 or .1 mpg?