My tire psi levels are at 30 for each tire. I drive a GMC Terrain. When should I start to think about putting air in them?
Check the pressure with a pressure gauge regularly, when it drops 2 psi below the recommended pressure, top them up. Always measure the pressure when the tires are cold (car's been sitting for a few hours in the shade).
There's a sticker, either in the glove box or on the driver door pillar that says what the recommended pressure is. Keep it within 2 psi.