http://www.tirerack.com/a.jsp?a=HP5&url=/index.jsp
Tires are usually considered legally worn out when they reach 2/32″ of remaining tread depth. Concerned that nearly worn out tires sacrifice too much wet traction, Tire Rack compared the stopping distances of new tires to those with 4/32″ and 2/32″ tread depth. The Tire Rack test results might surprise you!