I thought this was interesting for those who run tires down the the tread limits:

Stopping a Car

Even though the speed to begin braking the 3,400-pound BMW sedan was 20 mph higher than the 50-0 mph braking tests we conduct at The Tire Rack, the braking forces developed by the new tires felt reminiscent of full tread depth tires we've experienced on our home track. The car pitched forward as the brakes were applied, quickly took a set and slowed the car with authority. After repeated runs we learned that the average stopping distance for the new tires from 70 mph was 195.2-feet in 3.7-seconds.

Testing tires with the 2/32-inch minimum legal tread depth taught us the probable origin of the driver's accident report statement, "I hit the brakes hard, but nothing happened." There was a perceptible delay while waiting for the braking forces to grow after initiating the stop. Looking at the graphs recorded by the DriftBox confirmed this discomforting situation when we realized we were still traveling at about 55 mph on the tires with 2/32-inch of remaining tread depth when we reached the same distance it took the new tires to bring the BMW to a complete stop! This time the repeated runs taught us that the average stopping distance for the still legal 2/32-inch deep treaded tires from 70 mph had almost doubled to 378.8-feet and took 5.9 agonizing seconds to accomplish. We had the same car and the same brakes, but the tires with minimum legal tread depths weren't able to generate enough traction on the wet road to bring us to a quicker stop.



They ran the same tests with an F-150 and the stopping distance from 70 mph was nearly 500'.

http://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=85