I think the penny method is a good way. Or stop in at an auto tire store and use their gauge. 17,000 miles seems about right for the Metzlers. I would think you could even go 20,000 plus. They just look like they have more tread then the Bridgestones. I have 16,000 plus on my original Bridgestones. But the front is way gone. I'm going with the Metzlers when I replace them. The Avons just seem to wear too fast. I can't afford to replace tires every 6,000 miles.

"Catching a yellow jacket in your shirt at seventy miles per hour can double your vocabulary" Author unknown