Ran two tanks of fuel through and have a solid 10 - 11 mpg drop after installing the "winter" tires (BFG g-Force Comp-2 A/S). They are GREAT for the wet roads and actually do quite well in the snow. They are also Super sticky on the dry pavement and NO hydroplaning experienced yet, even in heavy rain and standing water situations. So far, worth the cost and the MPG drop ... for now. (Summer tires are Pirelli Cinturato P7's. 48 mpg average) MJ
Tire pressures the same? Add in winter gas formulation effect. Add in effect of rain and snow. I got a 3 MPG drop in winter with the same tires on summer and winter. But cold air reduced the tire pressure. And they do reformulate gas here.
I also get a pretty big drop in the winter. More time to warm up the engine upon start up, maybe running more to heat the car (especially on short trips in town), etc.
That is 10 out of 48. Between tires, temperatures, seasonal fuels, wind, and water and snow on the, that doesn't seem unreasonable.
Tank averages for our 2012 Prius v Five usually range between 34 and 37 mpg when it's on its BFG g-Force Comp-2 A/S tires in 3-season use which is about the same as when it is on its smaller 195/55-16 Winter Blizzak WS70 tires on steel wheels. The mileage hit from going to the original LRR 17" Toyo tires to the g-Force Comp-2 A/S was around 3 mpg. The tank averages when on the OEM Toyo tires were usually between 37 and 40 mpg. The car is used mostly on city streets at no more than 45 mph, trips less than 5 miles and is driven less than 5,000 miles per year. I keep tire pressures on both summer and winter tires at least above the minimums on the door post but keep them on the low side for comfort.. The g-Force Comp-2 A/S rides so much better and has so much better traction than the LRR Toyo tires. I never thought of the Comp-2's as being suitable for Winter but maybe they are for the Seattle area. I noticed when we were in Seattle in January than none of the family members had Winter tires on their vehicles. They've all (multiple households) since moved to central Washington where there is far more snowfall so maybe they'll be getting Winter tires.
Just to buck the trend, we're doing better with our snows. That's coming from (new this Spring) Michelin Primacy MXM4 215/45R17, on the porker OEM 17" rims, to Michelin X-Ice2 195/65R15, on steel Corolla 15" rims, going on for their tenth winter, still around 7/32" tread depth, and no cracking.
Mendel's post made me think of something that I don't think has been mentioned yet although Offline alluded to it. Different actual diameters will make it appear on the odometer that the car has traveled different distances. This would affect both the mileage display in the car and hand calculated mileages using the actual gallons at the pump. When I ran Mendel's sizes through an online calculator, the actual diameter of the 15's were about 1.5% larger than the others. Although in his case, bigger tires appear to be getting better mileage so that theory isn't perfect either.... I don't have any sense how accurate the calculators are- seems like there are other factors like sidewall flex, etc, that could make a difference. His diameter difference wasn't much but I suspect we can fit tires that would have a greater difference.
My 17's have a slightly smaller OD, at least by the stats, so that would mean they're mpg is even less. That said, highway driving and glancing between our Garmin and the speedo, the diff seems about the same; I think the in-practice revs-per-mile is so small as to get lost in the noise. Compounded by: the 17 Primacy are brand new, full tread, and the X-Ice are around 7/32" remaining tread.
Got a used 2015 Prius 4 the owner had put 17-in Enkei RPF-1 wheels with Continental DW 215/45/17. Tend to get ~40-45mpg with 40psi in all tires. Tires HOWL on rough roads. Hate that tire noise. Can't carry on a conversation with a passenger, let alone the back seat. But otherwise they perform well generally.Just don't have any other experience with this car and other tires. Just switched out to Bridgestone Blizzak WS80 195/65/15 snow tires (40psi also). By size calculation they are quite close, so the mpg should not change markedly on that basis. I expected to have a mileage loss and MORE noise. Nopel I like these tires a LOT better, completely ignoring their specialty designation. They ride better, are much quieter, AND get about 5mpg better. I like the car a lot more now. Think I'll be summer tire shopping. Anyone got suggestions for QUIET tires in the 17" size, that aren't useless in the rain (Seattle resident), and get decent mileage?
Winter gas formulations in cold climates have about 2% fewer BTU's and therefore everything else being equal, the car will use about 2% more fuel. Hypermilers look for 100% pure gasoline without the 10% ethanol when going for personal records. It's also a good idea check the calibration of the odo with a GPS and the car's displayed fuel consumption number with corrected odo distances and the gas pump volumes. You will need to average it over several fillups as the pump volumes can vary a liter or two. The pump reading will be very accurate but the filling has a few variables like sensitivity to clicking off, slope of the car etc.
Put 3500 miles on a brand new set of Blizzaks during a 6 week trip from Portland to the Coachella Valley and back in Jan. and Feb. We averaged 44.5 mpg in our 2013 Prius 2, now with about 150k on the odo. Earlier similar trips with Ecopias gave us around 50, so a drop of about 5 mpg, which I thought was pretty bad before I saw that 10 mpg drop mentioned above! Of course, the weather in SoCal made the winter tires totally superfluous, but they seemed like a good idea when we left home in the direction of Siskiyou Pass...
