Using The Chalk Method for Determining PSI
Using The Chalk Method for Determining PSI - NOTE. This article is posted for reference only. You should always consult with your local tire installation professional(s) when you have questions about your tires.
The “Chalk” method is a no-tech life hack that is commonly used by those who run larger off-road tires to determine PSI for pavement pounding (Highway Speed Driving). The “Chalk” method easily indicates if your tire’s tread has too much of an arc (convex shape of the tread) from too much pressure, or if it is slightly concave from a lack of pressure.
Here are the simple tools you’ll need to use the chalk method to figure out a satisfactory PSI for your tires:
- Chalk
- A tire pressure gauge
- Air (to fill up your tire)
- A pen and paper (for noting PSI)
- A dry, flat hard surface for testing.
With all of your materials and tools collected, 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. If you opt to do it in the road, please be careful and watch out for traffic. An empty parking lot is probably a more desirable location.
Air your tires up to maximum inflation. This should be marked on the side of your tires.
Next, draw a thick, straight line across the width of the tire. You’ll want to “chalk” the tread blocks all the way across (in a straight line) including the outer lugs. You may need to chalk two rows to get a good covering.
Now drive your vehicle in a straight line forward for about one complete car length.
Get out and inspect the chalk mark left on the ground and on the tire. 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. An over-inflated tire will bulge (or crown) and only the center of the line will touch and be left on the ground. In this case you will only see a small portion of line left on the ground. Since you are aired to Max inflation, then this is what you should see.
Let out about 3lbs of air, and repeat this process.
As you test your tire this way you will start to see a more complete line of chalk on the ground. You will have to keep letting air out until you see a complete line of chalk on the ground.
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.
You will need to keep adjusting your tire's air pressure according to the chalk test results until you find the pressure that is satisfactory to you. Keep in mind that you will need to do this test on both the front and rear tires to find the proper inflation for both which may or may not be the same. Record this information and keep it in your vehicle for future reference. As your tires wear you may need to perform this test again to confirm proper PSI. Also
A Word of Caution: The proper air pressure for the original equipment tires has been determined by the vehicles manufacturer, but when larger tires are installed the air pressure recommended by the factor for the original equipment tires may not apply to a larger size tire. Two things come into play concerning the load carrying capacity of tires. These two things are; the volume of air and air pressure. The larger tire has the greater volume of air. When attempting to determine an air pressure number by using the “chalk” method you may find that the tread foot print is nice and flat at a very low pressure. When this is the case the air pressure you come up with may very well be too low for highway service. Even though the “chalk” test gave you a full tread contact patch, at a low pressure the tire may not be stable at highway speeds. The large volume of air can support the load, but the low pressure causes the tire to become unstable. If air pressure is too low for highway service the tire will run hot from over flexing and will cause fast tread wear due to the “squirming”. This overheating can also cause a tire to fail.
Another Chalk Method for Determining Proper PSI
Air your tires up to maximum inflation. This should be marked on the side of your tires.
Draw a thick, straight line across the width of the tire. You’ll want to “chalk” the tread blocks all the way across (in a straight line) including the outer lugs. You may need to chalk two rows to get a good covering.
Now drive your vehicle in a straight line forward for about 50 to 100 feet. Stop. Then back up in the same straight line back to your starting point. Get out and inspect the chalk mark on your tire. Since your tire is at max inflation only the center part of the chalk should be erased. An over-inflated tire will bulge (or crown) and only the center of the line will touch the ground thus erasing the chalk.
Let out about 3lbs of air, and repeat this process.
As you test your tire this way you will start to see a more of chalk removed across the line you chalked on your tire. Keep adjusting your tire's air pressure by letting out 3lbs of air at a time according to the chalk test results.
If you let too much air out you will see that there is more chalk in the center of the tire and it is erasing from the edges. This is because the weight of the vehicle is pressing more on the outside of the tire, and the middle section is not making contact with the ground. If this happens add back air and retest.
You will need to keep adjusting your tire's air pressure according to the chalk test results until you find the pressure that is satisfactory to you. Keep in mind that you will need to do this test on both the front and rear tires to find the proper inflation for both which may or may not be the same. Record this information and keep it in your vehicle for future reference. As your tires wear you may need to perform this test again to confirm proper PSI. Also
A Word of Caution: The proper air pressure for the original equipment tires has been determined by the vehicles manufacturer, but when larger tires are installed the air pressure recommended by the factor for the original equipment tires may not apply to a larger size tire. Two things come into play concerning the load carrying capacity of tires. These two things are; the volume of air and air pressure. The larger tire has the greater volume of air. When attempting to determine an air pressure number by using the “chalk” method you may find that the tread foot print is nice and flat at a very low pressure. When this is the case the air pressure you come up with may very well be too low for highway service. Even though the “chalk” test gave you a full tread contact patch, at a low pressure the tire may not be stable at highway speeds. The large volume of air can support the load, but the low pressure causes the tire to become unstable. If air pressure is too low for highway service the tire will run hot from over flexing and will cause fast tread wear due to the “squirming”. This overheating can also cause a tire to fail.
