I'm told tire air pressure should be within 15% of the tire's max. True or false?

Dear Car Talk

Dear Car Talk | Jan 01, 2002

Dear Tom and Ray:

Recently, I was told by my mechanic that one should keep one's tire pressure within 15 percent of the maximum stated on the tire. What is your take on this? -- Hank

TOM: My take is that I would take my questions to another mechanic, Hank.

RAY: The proper tire pressure is listed on the glove-box door or on the driver's door pillar. That's the pressure that represents the best combination of attributes such as handling, braking, comfort and mileage.

TOM: When you change your tire pressure, you alter that matrix. For instance, if you add more pressure, you might get better mileage, but less comfort and poorer braking. If you put in less than the recommended pressure, you might get a softer ride, but poorer mileage and handling.

RAY: So unless you have a specific reason to alter the pressure (like you're carrying two mothers-in-law), use the recommended pressure as your guide.

TOM: The "maximum" pressure listed on the tire is just what it says, a maximum. That's the greatest amount you can safely put in your tire without damaging it. And your mechanic's advice to stay "within" 15 percent of that number suggests that you could be 15 percent ABOVE it as well as below it. And that's absolutely wrong, Hank.

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