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4x4 Tire Pressure Pointers

Posted in How To: Wheels Tires on April 1, 2012
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Photographers: Judy Reed

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.

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.

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:

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.
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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.

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