Rick's Free Auto Repair Advice

What’s the correct tire pressure?

What’s the correct tire pressure?

People ask this all the time. Each car maker installs a label either on the bottom edge of the driver’s door or the driver’s side pillar. It shows the recommended tire pressure for your vehicle. The manufacturer calculates the pressure for your particular car based on the weight of your engine, transmission, and accessories and the load rating of the tires. If you change to a different size tire with the same load rating, guess what, the weight of your vehicle hasn’tt changed and you must use the same tire pressure as listed on the label. Get it? Regardless of which tire you install, as long as the tire has the same load rating, the manufacturer’s tire pressure is the same.

The myth that overinflating tires saves gas

Some jerks don’t go by the label and inflate their tires to the maximum psi listed on the sidewall. They claim this increases gas mileage. Well, it does, but only slightly. The higher pressure reduces rolling resistance and that’s what gives you better MPG. But there are other costs that far exceed the gas savings. Plus, there’s a major safety factor you compromise when you over inflate. I’ll review the added costs and the reduced safety factor.

Over inflating a tire wears out the tire faster

When you inflate a tire beyond the recommended pressure, the added pressure lifts the tire shoulders off the pavement, causing you to drive only the tire wear diagramcenter tread. That means you have less tread in contact with the road, which means you have less traction, longer stopping distances, and faster tire wear. Less tire contact also GREATLY decreases the tire’s ability to remove water, which means you’re at a much higher risk of hydroplaning.

Overinflated tires wear out your suspension components faster

An overinflated tire has less flex so it doesn’t absorb road shocks. Instead, the stiff tire transfers every bump and dip to the suspension. So overinflated tires spend more time bouncing after a bump because it can’t absorb as much shock. The added bounce wears increases the movement cycles on your ball joints, tie rod ends, control arm bushings, and shocks/struts, so they wear out faster. The added gas mileage is actually false economy because those parts cost far more than any gas you might save.

Over inflation compromises your safety

Over inflated tires spend more time bouncing which means thens spending less time in contact with the road. That means poorer handling in turns. Since the over inflated tire is riding only on the center tread, it has less rubber-to-road contact. Less rubber contact means less control. Worse than that, however, is that less rubber contact means dramatically increased hydroplaning on wet surfaces.

The tread blocks and sipes (grooves molded into the rubber tread)

tire sipes

Tread sipes squeegee water and move it off to the tire shoulders to reduce hydroplaning

work like squeegees to wipe water from the center of the tire out to the edges where centrifugal force throws the water off the tire. When you over-inflate, the majority of those tread blocks and sipes no longer touch the road, so they can’ move the water. You’re literally skating on water.

Bottom line: over-inflation is stupid. It’s dangerous. It’ll wear out your suspension faster. You’ll have less control, especially in turns. And, if you get into an accident and the insurance company discovers that you’ve over-inflated your tires, they’ll strip you clean. It’s negligence. Good luck finding a new place to live. You’ll be lucky to walk away with the clothes on your back.

What does maximum tire pressure mean?

The pressure indicated on the tire sidewall is the maximum allowed in the tire, irrespective of the vehicle. It is NOT the recommended pressure.

How often should you check tire pressure?

Monthly, when tires are cold

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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