First off what is the right tire inflation for my 2004 kia spectra ls. also Iwhen I have passengers get in the back seat the car seems to sag. when they exit it seems to go back up. Runs good with no passesngers in the back. It has 90,000 miles.
What does your owner’s manual say? if you don;t have that, the correct tire pressure is also in the plackard in the front door jam.
The springs are supposed to compress when loaded. That’s normal. If you’re uncertain if yours is right, have it checked by a chassis shop.