Don't look at the tire, look at the door jamb sticker of your X to determine pressure!

The sticker will specify tire pressure assuming OE-equivalent tires (same tire size, same tire weight rating, etc). You need to follow this because this spec is taking into account the weight and handling characteristics of your X. Tires usually only specify maximum psi on the sidewall, not optimal psi (which is vehicle dependent). My 1st gen door sticker says 35psi (I have a supercharged with came stock with 17" rims, I think regular 16" Xterra's might 33 psi).

Now, this is for optimal balance of safety, feel, and fuel efficiency on pavement. Running tires at a higher-than-spec pressure will equate to a harsher ride, less traction, and potentially a bit more wear and tear on suspension components (if you're on rough pavement), but WILL increase fuel efficiency.

Off-road is a different story. Most people will air down off-road to have better grip and a smoother ride. If you have off-road worthy tires (ex: BFG KO2s for example), you can air down a lot b/c the tire has a lot of lateral support from a stiff bead.

 

That might be the Max Cold PSI. You don't want to run it at that! You want to use something at or close to the recommended pressure for your vehicle. 26PSI I believe was normal for first gen Xterras with 265's from the factory. I usually went a little higher, around 29.

 

@Wild Coast is correct. Note that the max pressure may catch your eye vs the recommended pressure. If you are putting in max pressure when in the morning in Florida in the 100 deg summer after driving, I'd be curious (NOT asking you to do this!), what the pressure must be then.

 

You'll find the manufacturer's optimum or recommended tire pressure for your car on a sticker in the door jamb, or in your owner's manual. Some models even place the stickers on the trunk lid, in the console, or on the fuel door.

 

You can also do the chalk test to determine the proper tire pressure for your rig.