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Car Tire Tread Wear

Conventional automotive wisdom says that if you can see over the top of Lincoln’s head when you stick a penny into a tire’s tread groove, that tire is down to 1/16-inch of tread thickness and should be replaced.

At that point, you should also be able to see a “treadwear indicator” in the tire itself.

All manufacturers include these indicators, which are raised sections at the bottoms of the tread grooves that become exposed when a tire wears down to 1/16 inch of remaining tread depth. But you shouldn’t wait that long to buy new tires.

Although most states allow a minimum tread thickness down to 1/16 inch (more precisely, 1.6 mm, or 2/32 inch, as manufacturers gauge tire depth), even a fractional amount of additional rubber can improve your stopping distance—and driving ability—by a considerably safe margin.

The Tire Rack, an online discount retailer, tested vehicles in 2007 and found that tires with 1/16 inch of tread averaged 499.5 feet to stop at 70 miles per hour. How much is that? Would you believe nearly a tenth of a mile—the length of a dozen school buses!

Then vehicles with double that amount of tire tread depth (1/8 inch, or 3.2 mm) were tested. This shortened the stopping distance by 122 feet—equal to three school buses, but still requiring nine bus-lengths of roadway to come to a dead stop. Think about that the next time you’re driving the kids to school.

To be safe, don’t wait until your tires are worn to the minimum. Older, balding tires are also more vulnerable to blowouts, punctures and other kinds of road damage. The new recommended home tire-replacement gauge is now a quarter instead of a penny. With a quarter, if you can see the top of Washington’s head, your tire is down to 1/8-inch (3.2mm) of remaining tread. That’s double the legal limit but, in practical terms, twice as safe.


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—Michael Morris for HomeTips

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