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      10-17-2012, 08:14 PM   #24

Drives: 2009 135i 6MT
Join Date: Feb 2010
Location: Maryland

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2009 135i  [3.25]
Originally Posted by Errowen View Post
The wear bars indicate whether the tire is safe to drive on, but they don't indicate whether the tire will still do the snow job. I think a snow tire's grip is a function of the sharp edges on the hundreds of sipes in the tread blocks -- at the micro level, those edges slice the ice just like a skate blade. Once those sipe edges are rounded, the tire's icy road performance will be gone, regardless of how much tread is left.
My winter tires have two sets of wear bars, 6/32" and 2/32". So did some Goodyear winter tires I was looking at. But others apparently don't have the 6/32" bars. The article on tread depth at Tire Rack says,

Because tread depth is such an important element for snow traction, winter tires usually start with noticeably deeper tread depths than typical All-Season or summer tires. Some winter tires even have a second series of "wear bars" molded in their tread pattern indicating approximately 6/32" remaining tread depth to warn you when your tires no longer meet the desired tread depth.