What should my 2005 Honda Civic's tire pressure be at?

My 2005 civic sedan's manual says tire pressure should be at 30 psi. The tires on it are Definity hp100's and the current pressure in them is about 42 psi. Is that because the particular tire can't go down to 30 psi? Or can they and should I drop them down to 30 psi?

Always measure your tire pressures when the tires are "COLD". That means after the car has been parked overnight, or at least several hours, and preferably indoors or in the shade. DO NOT adjust tire pressures when the tires are hot to the touch.

If the tires on your car are the same size and construction as original equipment, then use the information found in the placard (sticker) on the driver's door post. If they are different that the OEM tires, then you may have to adjust your tire pressures up or down a bit, but the factory settings are a good place to start.

Manual says tire pressure should be at 30 psi… So 30 to 32 psi should be about correct. I would never run 42 psi.

Stop by your local tire shop. They will adjust the pressure according to the tires you have. If you do not have the stock tires, the pressure may be different than what the manual says.

For normal operation, you should set the pressure to whatever it says in the driver side door jam. If it says 30psi, then set it to 30psi.

The engineers and designers at Honda determined 30 PSI was the best suitable tire pressure for your Civic. You should trust their findings. Sure, you can go a couple pounds over if you wish, but anything more would give you an unnecessarily harsh ride and could prematurely wear out your tires.