What are a few missing psi here and there? Quite a lot if they mean $5,500 for a new set of tires. As mundane as checking pressure is, it’s one of the simplest ways to hold down your costs because it prolongs tire life.
When a tire is underinflated, it’s under stress. Tires are designed to have certain tension on the belts, but those cables become fatigued when pressure is low.
“You’re susceptible to what we call a zipper rupture on the sidewall,” says Doug Jones, customer engineering support manager for Michelin. “It’s like if you get a metal clothes hanger and bend it back and forth – eventually it will snap.” Once a cable breaks, it begins damaging others around it, resulting in the zipper pattern.
Overinflation, too, forces a tire to operate outside its design. Hard tires not only give you a rough ride, but they, too, get fatigued because they cannot properly absorb impact. Also, overinflated and underinflated tires tend to run hotter, and heat breaks down the rubber.
Tires will pick up some heat, and therefore pressure, once you’re running, even on a cold day, so it’s best to check them when they’re cold. If you do check hot tires, it’s usually best not to deflate them because this could cause underinflation when they cool. However, imbalances of 10 psi or more between duals or between left and right steer tires need to be corrected to avoid tire damage.
What is the optimal pressure? A common mistake is simply going with the maximum pressure listed on the sidewall. “That’s the pressure for the maximum load, and most trucks don’t run the maximum load,” Jones says. Instead, he recommends checking the manufacturer’s guidebook or the truck’s data plate and adjusting as necessary to compensate for load, application and other factors.
This is where psi translates into miles, and miles into dollars. Michelin estimates that a tire consistently 20 percent underinflated will lose one-tenth to one-third of its tread life – 45,000 to 80,000 miles. While 20 percent might be extreme, even 10 percent too much or too little air means losing 5 percent to 15 percent of the tread life.
That’s hundreds of dollars a year in unnecessary retread or new tire costs. Give your tires the attention they deserve on your pretrip inspections, and you’ll be putting money in your pocket.