Tire Chalk Test - How to guide

This method of checking tire pressure, called the chalk test, demonstrates if your tire is bulging from too much pressure or if it is slightly concave from a lack of pressure



Instructions

1. Fill the tires to a good starting pressure. If you are unsure what pressure to start with then subtract 10 percent from the manufacturer's maximum inflation pressure on the side of the tire. If, for example, the maximum is 40 psi, then 10 percent of 40 is 4. Subtract the 10 percent value from the maximum psi value. So, 40 - 4 = 36. Use 36 psi in your tires. You could also use the following calculation for the starting pressure.
   • Weight of vehicle / (Manufacturers weight rating x 4)) x Manufacturers inflation pressure at weight rating
2. Drive to a flat area. This can be your driveway or the street in front of your house. Just make sure there aren't a lot of cracks, bumps or pot holes in the ground.
3. Using chalk, draw a thick, straight line across the width of the tire.
4. Use Test Variance 1 or Test Variance 2 for the completion of the instructions.

Test Variance 1

1. Drive the truck forward at least one-full truck length.
2. Inspect the chalk on the ground. A tire with the proper air pressure should press the chalk line evenly across the ground. This means you'll see the entire chalk line imprinted on the ground. If your tire is over-inflated, you'll only see a small portion of line in the center. If you're tire is underinflated, you'll see only the sides of the lines since the middle of the tire is not making contact with the ground.
3. Adjust your tire's air pressure according to the chalk test results and try again until you get the chalk line to press evenly across the ground.

Test Variance 2

1. Drive the truck to the end of the street and back or around the block.
2. Inspect the chalk on the tire. A tire with the proper air pressure will show the chalk evenly worn across the tire. If your tire is over-inflated, the center of the line will be worn more than the edges. If you're tire is underinflated, the outer edges of the line will be worn more than the center.
3. Adjust your tire's air pressure according to the chalk test results and try again until you get the chalk line to evenly wear across the tire.

Over-Inflated = More wear on the center of the tire = center of chalk line visible on ground = chalk line worn more in center

Under-Inflated = More wear on the outer edges of the tire = outer edges of chalk line visible on ground = chalk line worn more on outer edges