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Old 08-03-2010, 03:35 PM   #16 (permalink)
bwilson4web
Engineering first
 
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Join Date: Mar 2009
Location: Huntsville, AL
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14 i3-REx - '14 BMW i3-REx
Last 3: 45.67 mpg (US)

17 Prime Plus - '17 Toyota Prius Prime Plus
90 day: 58.25 mpg (US)
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Quote:
Originally Posted by robchalmers View Post
I'm just trying to understand the Prius. I'm sorry if the title is a little sharp, but I'm not sure what the aim of the car is.

A few petrol cars here in europe can produce the economy figures the prius does. . . .
It might help to introduce you to the EPA web site that folks can save their mileage numbers:
Fuel Economy

There is a "Compare Side-by-Side" that allows selecting four cars in different years to see what USA drivers are getting:
  • 49.1 MPG (US gallons) - 97 vehicles, 2010 Prius, Midsize car, 35-60 range
  • 49.8 MPG - 14 vehicles, Honda Insight 2010, Compact Car, 43-60 range
  • 44.7 MPG - 10 vehicles, VW Jetta TDI 2010 (manual), Compact Car, 36-52 range
  • 44.6 MPG - 5 vehicles, VW Golf TDI 2010 (manual), Compact Car, 41-47 range
These are not lab tests but what owners of these cars are getting. In fact you can get their individual averages and look at the distribution to understand where the performance falls off.

We find that other web sites that track mileage seem to report similar results:
Fuelly | Share and Compare Your MPG

Notice that the Prius, unlike the other three cars, is considered a midsize vehicle. This means we have a tremendous amount of space for people or fold down the rear seats, our "stuff." Only the Jetta SportWagen comes close in volume but at 39.9 MPG, 33-52 range, it has significantly worse fuel economy.

Now there is a critical speed that separates 'hybrid mode' from 'engine on always' mode and in the 2010 this is ~46 mph (~73 km/h). Below this speed, the car automatically cycles between engine running and electric power depending upon the demand and amount of energy in the battery. What this does is instead of running at a very inefficient, low power mode, the engine runs at a little higher, more fuel efficient per kilowatt hour. The excess energy is stored in the traction battery so when it has enough, it stops the engine and uses the stored excess energy. It turns out the energy saved by running the engine at a higher power setting more than makes up for any conversion losses.

BTW, I quite agree with the auto-stop engine nonsense as being just that, nonsense. General Motors just killed their 'auto-stop' hybrids that they called "mild hybrid." They failed to save hardly any fuel and were dreadfully expensive. Fortunately, the Toyota, Ford and Honda hybrids don't do just 'auto-stop' nonsense.

I do hope you get a chance to test drive a Prius. We had rented one in 2001 for a couple of days but at the time, I couldn't justify it. Then in 2005, I bought a used, 2003 Prius when our Camry was lost in a rain-slick, street accident. I've never looked back . . . except for the first tank.

The older, NHW11 model Prius, 2001-03, has a 'knee in the curve' at 70 mph (112 km/h) that I didn't know about. So I drove that first tank at 75+ mph (+120 km/h) and got 39 MPG. Slowing down to just 70 mph increased the mileage to 49 MPG and 65 mph (104 km/h) brings it to 52 MPG.

The newer, ZVW30, has lower aerodynamic and rolling drag with a larger 1.8L versus 1.5L engine. I have to exceed 80 mph (128 km/h) to get in the 39 MPG range.

Bob Wilson

p.s. One caution, reports that Prius owners buy them for the image of being 'Greener than Thou' that is pure utter nonsense from Jeremy Clarkson . . . although there is the new Prius buyer ceremony:

They serve cake.
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Last edited by bwilson4web; 08-03-2010 at 03:54 PM..
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