On our 19, a 2010, we have about 45,000 miles on the tires. I have rotated them front to back without incorporation of the spare three times in our 23,000+ miles. Current tread depth is 2@ 5/32, 1@4 / 32 and the right rear scuffer @ 3/32. I'm going to put new ones on in the next couple of weeks. I'm easy on tires and brakes, always have been. I believe religious tire pressure monitoring is paramount to good tread life. I snug my bearings pretty tight , then back the castellated nut off to the first hole, then check after the first couple days towing when I am backing up onto the 2X6. No play, no wobble is very important too. Just my thoughts and what works for me.