Walk through any parking lot and look at the tires on the cars around you. Odds are a meaningful number of them are visibly low — and the ones that look fine aren't necessarily right either.

A tire can lose 25 percent of its proper pressure before it looks noticeably flat to the unaided eye. By then, it's already been quietly costing the owner money for weeks.

<h3>Why Tire Pressure Actually Matters</h3>

An underinflated tire has a wider contact patch with the road, which increases rolling resistance. The engine has to work harder to move the car forward, which burns more fuel. The U.S. Department of Energy estimates that for every 1 PSI a tire is below its recommended level, fuel economy drops by about 0.4 percent. That adds up fast across four tires and thousands of miles.

Beyond fuel economy, a soft tire flexes more with every rotation. That flexing generates heat, and heat degrades the rubber compounds inside the tire. Over time, it accelerates wear and increases the risk of a blowout at speed. The Department of Transportation has estimated that around five million gallons of fuel are wasted daily in the United States from underinflated tires alone.

<h3>How to Check It Correctly</h3>

Buy a digital tire gauge — they run about $10 and slip into the glovebox easily. Analog stick gauges work too, but digital ones are easier to read and more consistent.

Check tire pressure when the tires are cold. That means either first thing in the morning before driving, or after the car has been sitting for at least 30 minutes. Driving heats the air inside the tires and increases the reading, which will give a falsely high number. If you check after a drive, add about 3 PSI to whatever the cold recommendation is.

Find the correct pressure for your specific car — not on the tire sidewall, but on the placard inside the driver's door jamb. It's usually a yellow or white sticker. Some vehicles have different recommended pressures for the front and rear tires. The number on the tire sidewall itself is the maximum allowable pressure, not the target.

<h3>Once a Month Is Enough</h3>

Monthly checks work well for most drivers. A quick check before any long trip is also smart. Temperature changes affect pressure too — roughly 1 PSI is lost or gained for every 10°F change in ambient temperature. This is why the low-pressure warning light often flickers on during the first cold days of winter.

Don't rely solely on the tire pressure monitoring system (TPMS). It's only required to warn drivers when a tire is 25 percent below the recommended pressure — at that point, the tire is already in a compromised state. Regular manual checks catch problems long before the light comes on.

<h3>The Fix Is Free</h3>

Most gas stations have air compressors available. Some charge a small fee, but asking an attendant often gets it turned on for free. If you drive frequently, a compact electric tire inflator that connects to the car's 12-volt outlet is a worthwhile $30–$50 investment that lives in the trunk.

It takes about ten minutes to check and adjust all four tires. The payoff in saved fuel, extended tire life, and safer handling is a pretty good return on that investment.