Ok just got home. Here's a good chart to go by for LT tires:
http://www.trucktires.com/bridgestone/u ... k_Load.pdf

I just took a look at my wifes Liberty to give you guys another example of methods for determining tire pressure.

Using her 2008 Liberty Sport 4x4 vehicle placard:
GVWR is 5600. This is the maximum vehicle weight loaded to the max with cargo/people/etc.

5600/4= 1400 lb required for each tire.

OR, also given is the GAWR which is the MAX load for the front and rear axles.
Front GAWR = 2750. Divide by 2 for the tires and you need 1375 lb capacity for the front tires.
Rear GAWR = 3200. Divide by 2 for the tires and you need 1600 lb capacity for the rear tires.

Going back to the chart in the link above. An LT215/85/16 you'll see that at 35 PSI the tires have a capacity of 1495 lb which is definitely good, especially for an unloaded Liberty that has a curb weight around 4000 lb? Now if you're loaded to max capacity and want to make sure you're covered for that GAWR in the rear which requires 1600 lb, you can bump the pressures up to 40 PSI which gives you a capacity of 1640 lb per that chart.

Thus, anything significantly over 40 PSI in the aforementioned tire size is likely overkill.

In any event, i would still suggest keeping an eye on the pressures and tweaking them as necessary.

But one thing is certain.... 70 PSI is way too much.

And check your tire placard... my wife's 08 has a recommended inflation pressure of 33 psi for her p225/75/16. So the Guy may have looked at the charts for a P225/75/16 @40 psi (and I wonder if they derate that load for the Liberty like they're supposed to for full sized truck?)

Can you ask them for a copy of their chart?

My KJ states 33psi on the door jam,no way I'm I going to run that much as my tires have a max inflation of 35psi(2600lbs max rated weight,load range C).I run about 26-28psi and my KJ weighs 6000lbs(yes actual weight,not GVWR).Though my tires are in a whole new class when referring to psi's then stock sized tires.

The key that most people don't realize is that tire deflection is a function of vehicle weight, tire size and pressure. The increased psi for LT tires is to make the tires more firm under the same (load) to prevent heat generation in the plys. Running upwards of 50 psi in tires as light as a Liberty, even a fully loaded liberty, will have undesireable effects.

40 psi is suitable for a GAWR of 3280 lbs.... the Max axle rating for the vehicle is 3150. So if you need more than 40psi in those tires to support your vehicle then you're excessively over loaded. I don't know what type of people you drive around with.... but 50 psi would carry your Jeep loaded to Max capacity plus another 700 lbs. Think about it, the curb weight is around 4000 and the GVWR is about 5600.. does your gear and passengers weigh 1600 pounds? And would you ever load your Liberty to 2300 pounds over curb weight? Hell that's more than the load capacity for most full size trucks.

I wouldn't run over 40 if it was my vehicle. IMO there's no benefit to 50.... but there are negatives. $.02