Ok, maybe not
that big. Two tanks ago, I swapped out my winter wheel set up, which is a set of stock Mazda 3 alloy rims in 17 x 6.5 size with 215-50r17 Yokohama iceGuard tires. I replaced them with the original Mazdaspeed3 wheels in 18x7 size, with the original Bridgestone Potenza RE050s. I figured that the upsize in wheels would have a negative effect on mpg, but I was hoping that would be somewhat offset by the lower rolling resistance of the shorter sidewalled summer compound tires. Bad assumption on my part! I understand that 2 tankfuls does not exactly make for a scientific study, but as my habits and commute haven't changed, then at least anecdotally I'm seeing almost a 9% drop in mpg, versus the previous 4 tanks. And considering the warmer, less dense air along with the presumably better (non-winter blend) gas, both of which should have helped improve the mpg, that 9% could arguably be low.
Ugh.
If I hadn't just put in a bid on a new house, I'd be placing my order for some lightweight 17 inch Enkei RPF1s tonight, purely for scientific reasons
. I guess I'll just deal with the factory boat anchors for now. Hopefully, I'll be able to make use of my new ECU datalogging device and especially the advanced tuning capabilities it provides. I haven't seen any insights
here on how to best take advantage, and plan my tuning accordingly, but hopefully the local recommended tuner shops can shed some light with their experience, and tuning expertise. Of course, that comes at a cost too. Well, I hope to be reporting some mpg improvement back soon. Back to the drawing board!