I am getting over 50 MPG during warmer months along HWY 880 & 80 mostly flat area freeways, 47-49 during colder and wetter months in winter. I see that you are in the Bay Area also, what are you getting and what's your commute like? Ooops my rims aren't stock Prius 17", they are Corolla S wheels which are sticking out and supposedly hurt gas mileage due to being less aerodynamic.
I was just going to say your wheels look like a Corolla. But I like them. Is it normal for Touring Prii with the 17" wheels to get lower gas mileage? (my 15" tires give me a steady 56 mpg, hand calculated, dry weather, but that's all city driving.)
Lifetime mileage is at 4.9 liters per 100 kms, translates to 48 mpg, still with the original Michelin Pilot hxMXM4 215/45R15.. That's with a mix of driving, varied trip lengths, me or my wife driving. Also, I switch to 195/65R15 Michelin X-Ice every winter, which seems to give about the same results.
If all variables stay the same, upgrade the 17" wheels/tires combo, most would agree a decrease of 2 mpg is normal, due to wider contact patch to the road surface and perhaps heavier wheels. At first I struggled to average above 50 mpg (calculated) when I switched to the Corolla S's, it was in the warmer months in June through August that I got 47-49mpg for a tank, but then soon after I got the average back to up over 50mpg a tank. I do think Prii look better in 17" wheels, may it be Gen 3 or 4, I have even seen Performance Plus Package wheels on a Gen 2 which I really love to have on my Prius. But if you are enjoying your 56 mpg and loving it more than the looks of the Touring wheels, then keeping the 15" gives you bragging rights in mpg wars with your friends, and more money for your wallet.
