What is mpg at 78-80 mph?

On flat ground, I see about 42-43 using the cruise control or at least maintaining constant speed.

 

Actually the Prius is a good alternative, assuming
- you're alone, so a light weight trip
- the low drag coefficient
- The Atkinson cycle engine versus the Otto cycle engine - 25% less power, but higher MPG, versus another car.

MPG varies by person, until you get used to it, or use the Cruise Control.
40k+ miles per year means you'll be in the car a lot, so you need to be confortable with the car's interior.

Rent a Prius for a week, and do a back & forth trip, do a Reset in the power usage screen to get a relevant MPG average for you. A rented Prius with 5k+ miles on it means you'll get a more accurate MPG than a brand new Prius.

On cruise control 90% of the time for the back & forth trip, you should get 42 Mpg or higher.

If you always creep up the the "other" guy in the left lane, having to slow down, then speed up again (possibly using the brake), you'll only get mid-thirties mpg.
However, any other car that has cruise control, use it, you'll get bettter mileage.

I typically get 40 Mpg on a 3,000 mile road trip, with the big THULE rack and two or three adults. *AND* I drive fast.
Meaning I follow the fastest driver when I'm not alone.

See www.GreenHuman.net that road-tested the Jetta TDI diesel and the G2 Prius some 7,900 miles, Portland-to-Portland. Both got low 40's.

The Jetta has better road handling, is more *comfy*, and with manual transmission costs more to own, more to fill-up, more to maintain, than the cheaper G2 Prius.
Not counting the fact that burning diesel or bio-diesel creates more airbourne pollution than the Prius PZEV exhaust.

However, if you're looking to save money, and you don't care about comfort, buy a used Toyota Echo or Yaris.
However I doubt they would be as stable in crosswinds at 80MPH versus the Prius.

 

In spring-like temperatures with no wind, Sdtundra's numbers are pretty close. The Prius MPG Simulator predicts 41.4 MPG at 80 MPH in 70F temperatures. That assumes near perfect conditions: steady speed, dry pavement, level terrain, no wind, 300# load (occupant and cargo), windows closed, no climate control used (or on vent), and Goodyear Integrity tires inflated to 44 front/42 rear.

If it's routinely windy in your part of NJ (e.g., near the coast), expect poorer results. A wind as light as 5 MPH (head- or cross-) will drop it to about 38 MPG at 70F.

Look for a drop in the winter: The simulator predicts 35.2 MPG at 30F (no wind). This assumes climate control on automatic with thermostat set to 72. All other variables remain the same.

Other factors that will reduce it further: continually speeding up and slowing down, hills, short trips, precipitation and wet pavement, heavier loads, lower air pressure, etc. You could easily get in the low 30s if the right combination of adverse factors is at work.

 

The new EPA subtests include a high speed segment in the neighborhood of the speeds mentioned. The new Prius coming out next month is expected to be a much nicer drive at high speeds than G2 in terms of road stability, and will get better mpg too due to the larger engine. 45+ mpg sounds about right to me.

My G2 Prius gets about 60mpg/60mph at high altitude, but the fuel economy drops off fairly quickly as the speed increases. Above 70 mph or so, and certainly above 75 mph, the G2 drivetrain loses some of it's sparkling efficiency. Enough in fact to put the car in the same fuel economy range as a VW diesel, as many a car mag has pointed out.

I am not advocating a diesel choice for OP, for these reasons:

• Much better reliability in a Prius
• Diesel is more expensive than petrol
• Diesel cars are heavier polluters -- including the newest models
• Off the high speed highway diesel mpg is mediocre.

The only reason I can think of to consider a diesel would be the superior driving dynamics so many people seem to report, particularly compared to Toyota which has a deserved reputation for middling driving dynamics. At a minimum I would test drive the new Honda Insight and G3 Prius if this was going to be a top priority for me.

 

I just took a 1200 mi trip along the E Coast after reaching 100,000 miles on my 2005.

Lifetime at 100K I'm averaging 47.8 mpg ( miles driven / gallons pumped ).

However the fuel economy differs by how much you push the vehicle. As noted by sdtundra on level terrain in normal weather at 75-80 mph you should get 42-43; I got 39-41 at that speed going mostly uphill from sea level to the mountains - into the prevailing weather. On the return trip at the same speed It was 45 mpg downhill with the wind.

At 65-75 mph you can expect 45-48 mpg most of the time.
At 55-65 mph you can expect 48-52 mpg very often.

Just drive it and look for chances to let off the pedal and coast.

 

I get in the 41-42 range when cruising at that speed.

 

We did a week's trip two weeks ago, 1,100 miles, on relatively flat terrain. We ran at 65-80 mph, and got about 46 mpg. Two adults, one child, some luggage. A previous 4,000-mile trip to Colorado, mainly flat terrain till New Mexico, netted about 48-56 mpg.

 

If you are going to use the Civic for comparison, look also at the Civic Hybrid. Many hypermilers over on cleanmpg.com prefer it over Prius on the highway, though you must be a serious hypermiler to get an advantage: Adapting Basic Hypermiling Techniques to the HCH-II - CleanMPG Forums

Note also that serious HM folks don't travel at your speeds, so I don't know what mileage to expect. And in city traffic, the Prius will chew up the Civic and spit it out.

 

I've driven from Denver to Omaha and back @ 75 mph with moderate ac and gotten 49 MPG on the way out and 46.5 MPG on the way back.

I did a drive to Lincoln, NE with similar speed and AC settings and got about 47 MPG going out and almost 50 MPG on the way back. Has about a 10 kt tail wind coming back (and it's uphill on the way back). So you can do well. I just set the cruise and went. Speed was VERY steady, which probably accounts for the good MPG.

 

My Prius feels perfectly good on the road at 108mph so not sure what you mean by unstable?

 

It is probably going to depend very much on what you consider comparable. You are likely to be surprised by the space in a Prius, it is deceptively roomy. However, if all you really require in a second vehicle is essentially a two seater (or minimal rear seating) and a manual transmission, then you can probably find something pretty inexpensive. Considering you are talking about ~12 hours a week behind the wheel, driver comfort/driving feel might be a bigger factor for you and worth several grand.

If you really drive it 40k/year then in a few years you will have driven any vehicle down to its minimum resale value. For far fewer miles/year a hybrid would typically recoup much of the premium.

 

i used to do this all the time with my stock tires.. and i still do with my current tires.

stock, you'll probably average 45 or so.. no lower than 40mpg.

with my heavy rims and worn suspension.. and much abuse to the car by this mileage... 38 to 42...

when i was doing cookie deliveries and keeping the route to city only, i would average around 52mpg...

worse comes to worse.. you hit some traffic and cruise... getting higher mpg.

 

Note the temperatures as it falls off in colder weather due to denser air and other thermal effects.

Bob Wilson

 

I drive I-57 from Chicago to Champaign IL. A few overpass hills. Generally some wind. I'm not a fan of the Prius cruise, but reluctantly use it. 75 mps for me is 40 to 41. Period. I am on replacement Michelin tires. After 48 - 52, the 41 seems kind of lackluster, but still pretty good. This is with two in the car.

 

Might be the tires. We tend to get around 44 mpg at 75 mph in hilly terrain on the Integrities at 42/40 psig.

 

this is an accurate statement based on my experience.
i drive about 20K miles/year.
i've found that staying under 65 and using the "pulse & glide" technique keeps me in the 50mpg range.
that is, i haven't re-set my display for over 16K miles and it currently shows 49.6 mpg.
that said, i live in a warm & arid climate, so i benefit from less ICE warm-up cycles.

BUT...all other things considered, expect 48-52mpg if you stay under 65mph.

 

Once you are up to high freeway speed, the advantage of the hybrid drop dramatically. At those speeds you are not using the electric portion of the drivetrain to any significant degree, and you are on gas power alone. I would be surprised if the "hybrid premium" is overtaken by fuel economy at those speeds. If you need economy, get a loaded Corolla.

 

The thing about the prius is not just about the electric motors, but a combination of factors. Specifically the Atkinson cycle engine and the low drag. Both of those always play a role no matter what speed your going.