Run mine on 36 even without a load.

 

What does the side of your tires say. My OEM tires state something like 40psi under load, that means when you have a load in the car you run the higher psi. Without load its 32.

 

Seems like there have been a lot of tire & tire pressure related questions coming up recently, so I want to make sure everyone clearly understands what the pressure numbers on the sidewall mean. If it is worded "Max Rated Load" or "Max Load" @ some pressure value, with a corresponding load value, it is the highest rated load carrying pressure for that given tire. It is not the max pressure that the tire will take before it is likely to rupture. You can also find your tire's max load capacity by referring to the load index on the tire and cross referencing this table. Note that the loads in that table are for the "Max Rated Load" pressure marked on your tire somewhere, not the vehicle manufacturer placard recommended pressure. This is typically around 36 psi for an SL tire and 42 psi for an XL tire.

If it says "Max Pressure" without any reference to loads, that is the max pressure that the manufacturer recommends putting in the tire under any condition.

Here are some good links to improve your tire knowledge if you are interested.
http://en.wikipedia.org/wiki/Tire_code
http://en.wikipedia.org/wiki/Tire

 

make sure you check the pressure in the tired after you load all your stuff into it. the extra weight puts more strain on it so check it after your loaded. not before.