I think the 5 MPG I am getting from my tail is ~95% of what a perfect one can get so the payback to change it is never.
Did you see my stickers? they are designed for looks AND for function, they cover the whole seam of car-tail. no leaks and better air flow
LRR tires we done back in July, +5 MPG from them.
With all the P&G I do, weight loss is a net 0 game.