Not long after the less dramatic sidewall blowout that inspired us to upgrade the tires on our family's 1970 GMC affectionately known as "The Beast," the spare decided to show off its ability to completely fail. The best tire from the shaded side of the truck is now being used as the spare, which made the upgrade much less expensive, plus a friend of the family was happy to barter some landscaping work for the old wheels and tires we didn't want to have to put up for sale.Not long after the less dramatic sidewall blowout that inspired us to upgrade the tires on You don’t need a tire blowout to have an excuse to upgrade your truck’s only contact points with the ground, but it’s good motivation. If you take this as an opportunity to upgrade the height and width to larger than the factory-equipped size, you can use chalk to make sure you don’t have too much or too little air pressure. Ignoring or just eyeballing the amount of pressure in your new tires can lead to premature wear and dangerous conditions such as excessive heat build-up, poor handling, and longer braking distances. Plus, you’ll get the best performance and fuel economy out of your truck when the tires are set up correctly. 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.Here are the simple tools you’ll need to use the chalk method to figure out your new tire Our family pickup is a ’70 GMC Sierra Grande ½-ton with the original 396ci big-block V-8 over the front tires, which travels only about 1,000 miles per year. After a decade of exposure on the driver’s side of the truck, the sun eventually took its toll on the sidewalls and caused a driveway blowout at the front left corner. The terribly out-of-style five-star aluminum wheels from the ’90s and mismatched front street and rear mud tires were upgraded to 31x10.5-inch All-Terrains all-around. The new gear was delivered pre-mounted and pre-balanced on some basic steel wheels. The bigger tires arrived with a good amount of air, but after testing using the chalk method explained in this article, it turned out they needed about 20 percent more pressure in each one. After the All-Terrains got up to the proper pressure, the pickup’s ride was better than it had ever been during the 36 years this GMC has been a part of our family. Here’s how we did it using just some chalk, a tire gauge, an air supply, an empty parking lot, and a little patience: Once you have your supplies, you’ll need to find an open and flat paved area where you can drive for about 50 feet in a straight line back and forth without being disturbed. Most streets are crowned so the rain will run down to the gutters, so you probably won’t be able to use your own street or any others to get an accurate reading. You should be able to find an empty parking lot at a local business during times when it’s closed, or churches up to six days of the week. Empty parking lots seem to work best because you’ll be able to take your time without getting in the way of others or having to deal with folks jockeying for empty parking spaces, and most are designed to be fairly flat.Once you have your supplies, you’ll need to find an open and flat paved area where you can After finding a flat place where you can drive back and forth for 50 or more feet, position the truck and draw a line across each tire making sure to get chalk in the middle and on the tread blocks closest to the sidewalls. If you can find an area with 100 feet of straight open space, that’s great, but 50 feet forward and 50 in reverse works just about the same. To prevent having to repeatedly move your truck a few feet to check your chalk lines, you can draw lines on the other sides of your tires, too. For the sake of safety, please resist the urge to put your truck in reverse and hang your body out of the door if you can’t get a good look at your chalk lines and need the wheels to turn another 1⁄4- or 1⁄2-turn. The worst part about getting run over by your own truck, other than potential death or horrible injury, is that you will probably become the subject of a story in the local news.After finding a flat place where you can drive back and forth for 50 or more feet, positio When you check the chalk lines on your tires after driving back and forth, you’ll be able to tell whether they are underinflated like the tire in this photo. It had the chalk worn off the outside edges because the center area of the tread pattern was not rubbing against the asphalt while the truck was rolled back and forth a few times in a straight line. A check with the tire gauge showed this tire was more than 15 psi below the eventual optimal pressure, which explains why the center of the tread was not being pushed into the driving surface.When you check the chalk lines on your tires after driving back and forth, you’ll be able The tire in this photo was purposefully overinflated to show how the chalk will rub off in the center of the tire tread and leave the outer tread blocks with less chalk worn off when there is too much air in your tires. That look is caused by the excess pressure making the tire bow in the center and leaving the outside blocks elevated off of the ground.The tire in this photo was purposefully overinflated to show how the chalk will rub off in This chalk line ended up a bit crooked, but after a few trips back and forth, with air being added at 5 psi per trip, this tire was the first to show even wear from one side to the other when it reached 30 psi. The other tires were brought up to this amount of pressure and all showed evenly worn chalk lines during the next couple of passes in the parking lot. When the truck’s new optimal tire pressure was applied at all four corners, the ride and handling felt excellent when it was taken out on the streets for a test drive.This chalk line ended up a bit crooked, but after a few trips back and forth, with air bei Once your new tire pressure is dialed-in, it can’t hurt to write it down and keep a copy in the glovebox. Then anytime you want to air-down, you won’t have to rely on your memory when you need to fill up before hitting the pavement. It can also come in handy for anyone who ends up borrowing your truck. You may want to keep the chalk in your vehicle, because you’ll need to use it again in about 500 to 1,000 miles after the sidewalls have broken-in and make sure your truck’s preferred tire psi is still the same.Once your new tire pressure is dialed-in, it can’t hurt to write it down and keep a copy i If your truck has to sit outside, you should consider buying sun-resistant covers for the tires that are left exposed. We bought tire shades designed for use on a motorhome to fully cover the new oversize tires. The spare will also get a tire cover; it’s exposed to all the elements, as well as everything that gets loaded into the bed and the water used to wash out debris. By Trevor Reed Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!