Tires can lose their footing long before they're worn out. Our
tests show that tread can give up a significant amount of grip when
it's still at the halfway point.
That's particularly worrisome when you realize how many worn
tires are on the roads. A recent study by the National Highway
Traffic Safety Administration found that nearly 50 percent of the
11,500 cars, pickup trucks, vans, and sport-utility vehicles the
agency checked had at least one tire with half-worn tread. Another
10 percent had at least one bald tire.
Worn tires-especially bald ones-can be deadly on wet roads,
where the grooves aren't deep enough to channel water out from
beneath the tread. The result is hydroplaning, where the tread
skims the water's surface and the vehicle no longer responds to the
steering wheel. Wet-weather braking and snow traction also decrease
as tires wear.
Tires are considered bald when one or more of their grooves
reaches 2/32 of an inch deep, compared with about 10/32 of an inch
for new tires (tread wear is usually measured in 1/32-inch
increments). Manufacturers have made bald tires easier to spot by
placing a series of molded horizontal bars at the base of the
grooves. The bars become flush with surrounding tread when wear
reduces a groove's depth to 2/32 of an inch. That's also the point
where tires will flunk a state safety inspection-and where tread
must be worn for you to collect on a tire's tread-wear
warranty.
Unfortunately, 2/32 of an inch may be too late if you drive in
rain or snow. Based on our tests of new and half-tread-depth tires,
you may want to consider shopping for new ones on your car or truck
closer to the 4/32-inch groove depth.
Source: ConsumerReports.org