quadruple hit to MPG

I'd say the combination of your speed and the roof rack. Just 5 - 10 mph off you your speed would have made a world of difference.

 

28MPG might not be that bad, considering the conditions. A month ago I had a tank average 39MPG (43.4 on the MFD) doing 75-77mph with the cruise, many hills, and similar temperature. To my advantage, I had decent LRR tires at 51PSI and no roof rack. I think its possible for the snow tires and rack to take off that much mileage, especially with how hard you're pushing the car just doing 75.

 

I still love it.
As long as I've followed Hybrids, Prius and Prius Chat, I've seen so many posts like this.

Personally? I love owning a vehicle that can have almost every possible strike against it as far as getting good gas mileage but still get an "awful" 28 mpg.

How quickly we forget that for almost every other vehicle on the market a 28 mpg average under "ideal" circumstance would be considered great.

Of course I watch my MPG, just like the majority of all Prius owners. But I try not to react to either one situation that creates momentarily astronomically great gas mileage, nor do I react to situations that are currently hampering my gas mileage. Ski racks, cold temps, fast speed, snow tires...all are applied situations that will lower your MPG and would with any vehicle.

If you remove or mother nature removes, some of those mileage killing scenarios, temps warm up, ski rack removed, snow tires removed, slower speeds embraced and your awful mileage doesn't improve? Then I'd worry. Given all the negatives applied to that trip? My guess would be your Prius was doing the best job it could.

 

Your Prius did far better than my 1997 Subaru Legacy GT Wagon (i.e. Outback clone) ever did on that road with a roof ski rack. And I never traveled above 70. While that car later produced low-to-mid 30 mpgs on other roads, it needed warm weather, lower speeds, and no roof rack, even the factory crossbars were removed.

Did you encounter significant winds there, as I have multiple times? In a Prius, a cross wind can be worse than a head wind. On almost this entire route, except maybe the portion from Twin Falls to Burley, the wind is almost guaranteed to be cross wind.

I hope to be driving that road again this winter, though in a '14 Forester, stick shift. So far, with no roof rack (skis inside), speeds below 65, and grill blocking, it is holding a smidge above 30 mpg. If you can put the skis inside your Prius (today's shorter skis easily fit inside mine), it will help greatly.

 

At some point maybe you could make a small test on windless level road, no racks, somewhat warmer, around 50mph, and find what the base line is for your car. You should be able to get an instantaneous 40mpg or more without much problem. As mentioned, if not, then start looking for things like 12V failure, alignment issues, etc.

I go up a large mountain, not very fast, and get 25mpg in the act. I remember to tell myself that the guy in the big 4wd V8 pickup that blasts by at high speed is only getting what....8mpg?

 

Was this the posted limit? Or your personal limit?

80 mph translates to 130 km/hr. I've never wound ours much past 100 km/hr. I think around here the highest posted limit is 110. And with those posted speeds, no one's going to fault you if you stay under, in the right lane.

Your speed is the "low hanging fruit". Especially with all the jewelry on the roof, lower speed is a dead simple way to improve mileage. And your odds of stopping in time...

 

Even with LRR tires, warm weather, no rack, at 80 mph you would expect only around 38 mpg based on bobwilson4web chart.

So 28 ish seems very fair with the cD killing roof rack and the snows and the cold.

 

What kind of fuel do they have out there? Is it 100% unleaded or 10% ethanol mixture? My mpg seems to drop a little more with the 10% ethanol mixture, especially in cold temps. Here in Oklahoma city we still have 100% unleaded at most stations, but thats supposed to be changing.

okcpriusguy

 

how many miles on her?

 

I would estimate that the snow tires could be about a 6 mpg or more hit. For me the difference between LRR tires and performance tires was about 6 mpg. Snow tire would likely be worse. When I had a bike rack on the back with two bikes I got about a 10MPG hit at highway speeds. 80 mph is also a big hit.
The Prius has one of the lowest coefficient of drag of any car, so stuff on the outside will have a significant impact. Also drag increases with the square of velocity, so if you double your speed the, drag force goes up by a factor of 4. So without doing the exact math, 80 is about %45 faster than 55 so your drag would roughly triple and then add that drag of the skis and ski racks and you have a lot of drag. Also the Prius has a small engine, that is just enough for the light weight, low drag car. The engine does not have a lot of excess horsepower to handle increased loads like cars with larger engines. I was surprised to see a 1o mpg hit with the bike rack and bikes. But considering I get almost 50 mpg without it I can live with the hit when I have the bikes on the back.

 

I drove to Florida and because of the flat terrain, not as much coasting. I drove around 80mph temps were mid 70's and avg probably 46mpg

SPH-L710 ?