High Speed MPG

It is well known that the fuel economy reduces exponentially as you increase speed. You will not get anywhere close to 50 mpg - 60 mpg going 80 mph+

I can get 50 mpg - 53 mpg at 60 mph quite easily.

 

This summer we drove the Prius from here in Southern California to Albuquerque, Denver and back. Most of it was in 100+ degree weather so the a/c was always on. Between Grand Junction, CO and Primm, NV was mostly 80 mph through Utah. Those two fills calculated at 42.6 and 41.8 with four adult sized people in the car plus luggage and ice chests.

Mileage for the entire trip was in in the 43s running at 75 mph most of the trip.

 

Last tank approx. 80% highway @ 65-70mph=45.5mpg (calculated) for me with constant a/c use this time of year.

 

Haven't driven enough on the highway enough yet with my new Prius to get a good benchmark; but, with my 2010 V with ATP I normally got 52-54 at 65-70MPH.

 

I gotten 50 MPG all highway driving for an entire day. Drove 161 miles. This is with an 09 Prius. I get between 50-70 MPG city.

Posted via the PriusChat mobile app.

 

I can get 50-55 mpg by keeping my maximum speed limited to 73mph (granted, I run my tires at 50psi). If you look at mpg versus speed plots for the Prius, it takes an especially large hit above 75mph (the below is for the 3rd, gen but the 2nd gen seems to behave the same way, getting just slightly lower mpg at each speed).

Preliminary 2010 mph vs MPG | PriusChat

The rule of thumb I've heard for highway travel is 63mpg at 63mph. To estimate mpg for a given speed, for every mph you go faster than this, subtract a mpg. So if you drive 73mph, you'll probably get 53mpg; 83mph would result in 43mpg. Conversely 53mph would net you 73mpg. I think this is a good estimate if you have low rolling resistance tires; you'll probably do a bit worse with more "normal" tires.

The Prius does seem to take an especially large hit above 75mph. I think the reason the Prius gets much worse fuel economy above 75mph is because the engine has to work too hard and its rpm rises out of its "sweet spot" (rpm and throttle range that give maximum horsepower per unit of fuel input). According to Hobbit, this is between 1400 to 2200rpm. Using my scanguage, at 73 mph on flat ground, my engine rpm stays between 2000 and 2200. If I go faster than this, I have to use a higher rpm which takes me out of this range. Also, 73mph is the maximum speed the engine can go into fuel cutoff while still staying at its minimum rpm: 960. If I go faster than this, the engine will still go into fuel cutoff, but the rpm is higher in order to keep MG1 from spinning at too high of an rpm. Obviously, a higher rpm results in more drag.

 

I did this just for fun without the ICE kicking in. I drove down a long flat road did a Ui and back around again going 30 MPG maintaining the momentum by coasting with no arrows and Glide on electric with yellow arrows and re gen braking at stop signs. No gas until I got off that road on to another one with heavy traffic and it started going down to 70 MPG. I was essentially EV during the entire 15 minute commute.

Posted via the PriusChat mobile app.

 

Posted via the PriusChat mobile app.

 

Amazingly, there is an entire class of vehicles doing so right now, in the right lane of the freeways I use. If you travel with the Semis, at the speed limit, the trip is 5 minutes longer and much cheaper.
In the cities I travel in the lights are timed, each one takes the same time to change as it did last time. You can learn the patterns and rarely have a last second stop.

It is possible you have few semis and that all your lights are vehicle sensitive and change only due to actual traffic.

 

I sometimes like to drive behind a semi. If I have a head wind that works wonders my fuel mileage. It easily jumps to 50 and 60 miles per gallon. Just keep 2 car lengths behind or more.

I have found that high speed hypermiling works. The speed range may be as low as 2-3 miles per hour.
Say, from 70 to 73 mph and then ease off the throttle until it's back to 70 mph. The coast factor of a Prius goes a long way.

My gen 2 (04) is slowly losing its fuel mileage. (Newer 12v battery) Maybe HV battery age (184771 miles) might be the cause.
My last trip this weekend resulted in 47 mpg running @ 70-75 with no hypermiling. When I got it 3 years ago I could easily do 50 mpg. I had 143K miles on it then.

There is several reasons for the no hypermiling, I had new shoes on and the throttle feel wasn't there. LOL

Second my Dash Dyno SPD fuel meter ate the SD chip and refused to work so I was driving "blind".
It is so much harder to hypermile with just the MFD.




This is the fuel mileage screen I use. Obviously the car wasn't a Prius.
The Dash Dyo SPD isn't cheap but it works very well. I bought mine from Amazon.