If all new tires are not equal, worn tires are even harder to compare.
Michelin conducted internal tests1 that compared braking distances among specific tires in new and worn conditions to reveal how safety performance changes over time. The "worn" tires were buffed to the tread wear indicator, near the end of the tire's useful life (at 2/32-inch, as defined in many states).
The test results are dramatic. Some worn tires deliver wet-braking distances that are about the same or better than other new tires. In fact, there was a 78-foot difference in stopping distance, more than five car lengths, between the best and worst tire in the test.
1 All tires wear out and should eventually be replaced. Based on internal wet braking test results from 50 MPH versus Pirelli® CinturatoTM P7 All Season Plus, Continental® Pure ContactTM All Season in 215/60R16 95V and Goodyear® Assurance® WeatherReadyTM All Weather in 215/60R16 95H tires machine buffed to 3/32” (which is above the 2/32” tread wear out limit in most states) on a 2017 Chevrolet Malibu. Actual on-road results may vary