I forget who, but someone on YouTube once calculated the economics of rotating tires...basically, unless you do it yourself or can have someone else do it for 'free' (say as part of an oil change service), then it is actually cheaper to just let the tires on 1 side (front or back) wear out and just replace those 2 tires when needed. Now this was a few years back and I believe they assumed a $25 service charge for tire rotation. Personally, I rotate my tires every 5-7k miles...either myself or part of a service package.