Worn Treads Can Lead to Unsafe Braking

 

Automotive equipment retailer Tire Rack released a new test video revealing how significantly tire tread depths, especially on severely worn or at-the-legal-limit tread tires, affect wet braking performance. Braking distances soared, in one example doubling the wet braking distance of new tires.   In the new  “How Tire Tread Depth Affects Wet Stopping Distance” test video Tire Rack’s TJ Campbell, tire information and testing manager, and Brent Rollins, assistant tire information and testing manager, set out to update a popular and helpful test first done by Tire Rack in 2007.    Like the original, they used a sedan with standard touring all-season tires and a pickup truck with highway all-season tires. Tests were on a straight road with 1 mm of water, simulating surface water conditions during a heavy downpour, and they recorded the stopping distances of brand new, severely worn, and at the legal limit tires. The tread depths were 11/32 to 12/32, 4/32, and 2/32 of an inch, respectively.

Using a sedan and pickup Tire Rack tested the wet braking performance of brand new, severely worn, and at the legal limit tread depth tires. The sedan's (above) the braking distance nearly doubled on at the legal limit tires.

Most alarming were the speeds each vehicle with at the legal limit tires (2/32 of an inch tread depth) recorded as they passed the point where the brand-new tires came to a halt. The sedan blew by the new tire stopping point at 50 mph, while the pickup passed at 36 mph. In any panic stop situation this likely would result in significant rear end collision damage and potential occupant injuries.   New tires have deep grooves that channel water through the tire’s footprint to provide traction. With severely worn and at the legal limit tires the test paints a clear picture. “Simply put, if the ground is wet and you’re hoping to come to a stop, the more tread you have on your tires, the better,” said Rollins.   Obviously, no one can drive on brand-new tires all the time because tires wear. But drivers should get years of safe use providing they follow routine maintenance like tire rotations and proper inflation levels, and while obvious it is helpful to remember wet braking distances increase as tires wear out.   So when is the right time to replace your tires? “We recommend replacing tires when you reach 4/32 of an inch of remaining tread depth, the distance between the edge of an inverted quarter and the top of President Washington’s head,” said Campbell. “This is like the traditional penny test, except the penny test measures the absolute legal limit, or 2/32 of an inch. Best to go with the quarter test because as our test shows the bare minimum tread depth in a panic stop means the driver and occupants are along for the ride, and a scary ride at that.”

While tread wear is noticeable among brand new, severely worn, and at the legal limit tires, always measure the tread depth. Tire Rack recommends replacing at 4/32 of an inch of remaining tread, the distance between the edge of an inverted quarter and the top of President Washington’s head. The traditional penny test measures the absolute minimum legal limit tread depth.