Rick's Free Auto Repair Advice

Tire pressure — recommended versus maximum

Tire Pressure

Recommended tire pressure is NOT the same as maximum tire pressure

Every 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 recommended tire pressure is based on the weight of your vehicle and the load rating of the tires.

If you change to a different size tire with the same load rating the recommended tire pressure doesn’t change. You still follow the pressure listed on the label.

What is the tire’s maximum pressure rating?

If you’re hauling a heavy load (up to the vehicles listed maximum payload) you can inflate the tires up to the maximum psi listed on the tire to help improve handling. Once you remove the load, deflate down to the recommended tire pressure.

Does over-inflating tires improve MPG?

Yes. But it costs far more in ways you don’t expect.

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. So your tires transfer  every bump and dip to the suspension. Overinflated tires spend more time bouncing and 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 they spend 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.

How often should you check tire pressure?

Monthly, when tires are cold

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat


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