First of all, how come I see so many IP addresses on your post?
Google say 50k miles, but I generally replace my tires every 3 to 4 years or when I notice they wear out. In most cases, they have more than 15k on them. I use two different sets of tires annually. At this time, I have Michelin Xi3, since it's winter. I plan to get a new set on 4wheelonline in a few months as this is the 4th season that I run the said model.