Here are the simple tools you’ll need to use the chalk method to figure out your new tire psi: 1.) Chalk. If you have kids, there’s a good chance there’s already some in the house—even giant sticks of colored sidewalk chalk can be used. Otherwise, you can usually find it in the office supply or children’s section at the drug store or supermarket. 2.) A tire pressure gauge. 3.) An air source. We used a carry tank filled with an electric compressor in the tool shed, but an inexpensive 12-volt compressor that plugs into the cigarette lighter outlet can also be used. Otherwise, you’ll have to make multiple trips to a filling station, and many are now charging a dollar or more for access to air. 4.) A pen and paper for noting the correct psi.