Calculated tire CPM?

[Rawze]

I have bridge-stone M710's.

They last me about 450k miles at a time. I replace them when they get below about 5/32" cuz I don't like em slipping in the rain.

There is roughly about a 0.7 mpg (increase) difference on average when their worn down to 5/32 vs. when they are brand new. Depends on how heavy we are, as to how much it shows though.