Keep On Rolling | Understanding What Tire Pressure Is Right For Your Truck
Tire pressure. Given the complexity of today’s commercial trucks, it might be hard to believe that something so small as a pound or two of air pressure could bring your truck to its knees. Believe it. Improperly inflated tires can cause numerous problems, large and small. These problems can reduce both your truck’s performance and your bottom line.
Truck tires are expensive. You want to get every mile possible from them. Road hazards and curbing can certainly cause blowouts, but the most common cause is under-inflated tire pressure. Drivers and fleet managers don’t always realize how critical this can be.
Unfortunately, tire pressure is not a set-and-forget service adjustment. As tires roll over the road, they seep air. Industry experts say that, over a month’s time, your tires will lose about 2% of their inflation pressure (by volume). That happens even when you ensure that casings, valve stems, and tire bead/rim contact areas are all maintained perfectly. If your wheel/tire assembly is less than perfect – a situation that’s not uncommon – you could lose 2% of tire pressure every week. Or more.
So the longer you wait to check tire pressure, the greater your air losses will be. Who cares?
Those same industry experts – the people who make tires – estimate that creeping deflation is responsible for 80% of blowouts. Running tires even slightly “flat” produces excessive sidewall flex and speeds deterioration of rubber compounds. Of course, your tire might not fail altogether. You could experience irregular wear, which negatively affects tire and truck performance. And you’ll probably see a drop in fuel efficiency.
All these costs are entirely preventable, if you simply check and correct tire pressure daily.
Identifying proper psi
Every tire manufacturer specifies an inflation level for each of their products. These recommended pressures are based on the size of the tire, how it’s constructed, and the load it will carry. Technically, the tire does not carry any load – it’s actually the air inside that provides the support. Given a specific air pressure, a bigger tire can usually carry a heavier load than a smaller one. That’s why load weight ratings differ by tire size at the same pressure.
The load range rating is specified by each OEM based on the particular tire’s design and construction, to ensure optimum sidewall flex and footprint size. Regardless of how they’re made, all tires have to meet industry and government standards.
Tire position matters, too, but not necessarily in the traditional sense. In the past, fleet managers have often assumed certain tire pressures were correct for certain wheel positions, regardless of the payload, road conditions, or the tire’s individual characteristics. But trucks and trailers are different today. Where steer axles used to run around 12,000 lbs., they now run at 13,000 lbs., or even more. That calls for a different tire pressure. To compare:
- With a 12,000 lb. axle and 11R22.5 and 295/75R22.5 tire sizes, you might have used a tire with a G load range rating and single load-carrying capacity of 6,175 lbs. Inflation would have been 110 psi.
- At 13,000 lbs., however, you’ll want an H load range tire with a single-load-carrying capacity of 6.610 lbs. Inflation should be 120 psi.
Each tire on the axle must be rated to carry the specified load – 6,000 lbs. on a 12,000 lb. axle, for instance. Otherwise, the tire is considered to be overloaded. Using the above example, tire pressure of 100 psi would provide load carrying capacity of just 11,900 lbs. At 90 psi, capacity would drop by a full thousand pounds.
Margin for error tends to be somewhat less for drive and trailer tires. Nonetheless, problems stemming from inadequate tire pressure multiply with each tire, especially for fully loaded tandem groupings. The bottom line, say tire professionals, is “don’t assume” a single tire pressure level is best for every tire. OEMs provide inflation charts to help you determine optimum inflation.
Experts also suggest making tire pressure monitoring a part of your regular maintenance program. Create documentation that describes target pressures. Train employees to check pressure frequently, using a calibrated air pressure gauge. Routinely inspect and rotate tires, inspect valves and caps, and check the truck’s wheel alignment. Conduct audits to be sure your plan is being followed.
Knowing how to identify and maintain proper tire pressure will keep your truck fleet on the road, rolling smoothly, and keep your bottom line pumped up, too.