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Car and Driver: The Truth About EPA City / Highway MPG Estimates

Discussion in 'Other Cars' started by cwerdna, Aug 14, 2009.

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  1. cwerdna

    cwerdna Senior Member

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    3 people like this.
  2. bluetwo

    bluetwo Relevance is irrelevant

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    Definitely very insightful. I never would've known about half that stuff. :)
  3. Tideland Prius

    Tideland Prius Moderator of the North Staff Member

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    Tons of information. Thanks for the article!
  4. SageBrush

    SageBrush Senior Member

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    Since CAFE uses the unfudged original EPA test data from the easy protocols, a bit of arithmetic shows that CAFE mpg is about 40% higher than current 'sticker' mpg.
  5. donee

    donee New Member

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    Hi All,

    Interesting article. On the issue of EV or PHEV 40 mileage, I think its silly to combine the electric power as if its a gasoline equivalent. Its commonly said it takes as much electricity to make that gallon of gas, as a sedan EV requires for the same distance as a traditional car can go on the gallon of gas. So, does one factor in that energy used to make the gasoline or not? If one just uses the energy content of the gasoline, that penalizes the EV wholistic energy consumption evaluation. If one uses the energy in the gasoline, plus the energy used to make the gasoline, that does not make driver experienced consumption easily related to the published results.

    I think there is no way to get around publishing both results seperatly. There should be both a MPG rating for the Charge Sustaining mode, and a Miles/KWH for the pure electric mode of the PHEV.

    And for CAFE purpose the MPG CAFE test rating in Charge Sustaining mode should be used. GM is making cars for customers, NOT THEMSELVES.
    1 person likes this.
  6. daniel

    daniel Cat Lovers Against the Bomb

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    Interesting.

    The whole business of converting kWh/100 miles into mpg is further confused because there are at least four different ways you could approach the conversion:

    1. Energy equivalent of the fuel itself.

    2. Energy equivalent of the fuel including the energy used to produce it.

    3. Environmental impact (carbon, etc.)

    4. Cost to run the car at present fuel & electricity costs.

    I would suggest providing several different figures on the sticker, on the grounds that more information is always better. Electrical appliances tell you the assumed cost of operation, and this is the bottom line for many consumers, so it should be included. For a PHEV the consumer should be told both the kWh/100 miles (or Wh/mile) in electric mode and the mpg after the grid charge is depleted. No combined figure can be truly meaningful because it depends so much on how much of your driving is electric and how much is gas, but a combined cost-to-operate could be given for several set distances, determined as likely commute distances.

    If both mpg or equivalent and kWh or equivalent were given for every car, people would get used to seeing both, and perhaps in a generation (after all us old fogies have died off) today's kids, as adults, would have learned to comprehend kWh.

    I'm pleased to see from the article that the Tesla Roadster gets 320 wh/mi. At 55 mph (faster than the EPA test average speed) my Porsche gets around 350 wh/mi., so my car is not doing as poorly as I thought, considering that the Tesla is engineered from the ground up, and my car is merely a conversion.
  7. ggood

    ggood Blue PIP Aficionado

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    The article said that Econ mode in the insight made almost no difference. People just compensate for the trick throttle by pushing the pedal further, which is what I've found in the Prius. There may be some marginal energy savings from cycling down the A/C, but I'll bet its not much, notwithstanding the anecdotal claims some people have made.
  8. donee

    donee New Member

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    Hi ggood,

    That is true in the test, but its not neccassarily so for driving. A lower pedal to power ratio makes it easier to modulate at low power levels for hypermiling. But, its up to the operator to do this, and in the test the operator is carefully controlled out of the evaluation.
  9. ggood

    ggood Blue PIP Aficionado

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    Haven't noticed that it made much difference for me, but then I have almost no opportunity (and am too lazy) to do any true p&g or hypermiling, so I'll defer to the experts...
  10. bluetwo

    bluetwo Relevance is irrelevant

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    I've always felt like different modes were a complete waste of time when it comes to fuel economy. Maybe there are people who use the exact throttle inputs for every situations and it might actually help those folks. I vary my driving so much an economy mode wouldn't do anything for me.

    Different levels of traction and stability control make sense for a sports car with different driving modes but not for economy, not to me.

    I do hope the EPA will do it's best to get the most acurate measurements possible as things change.
  11. cwerdna

    cwerdna Senior Member

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    While cleaning up my apartment, I found the print version of After 30 Years, the EPA Finally Comes up with Realistic Fuel-Economy Estimates - Column - Auto Reviews - Car and Driver. I figured it wasn't worth starting a new thread for this.

    I didn't realize the first part of this:


    Detailed Test Information just gives a lab temperature of 68 to 86 F for the old city, old highway and high speed portions.

    I had forgotten about the old highway test being so leisurely in its acceleration.
  12. Skoorbmax

    Skoorbmax Senior Member

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    Very very surprised that they have not created a basic robot with sensors to tie exactly into the computer that's telling the driver what to do. This would be harder for manual vehicles but for autos could physically actuate the accelerator pedal based on feedback from the computer.
  13. tomlouie

    tomlouie Member

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    Are you talking about how the article describes the EPA driver watching a video screen for throttle and brake cues during the test cycle?

    EPA computer -> human driver -> car controls -> car computer -> car

    Yeah, they totally need an automated system for operating the car during the test cycle:

    EPA computer -> car computer -> car
  14. ataylorracing

    ataylorracing ataylorracing

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    My wifes last 4 tanks of all in town driving was 48+, 50+, 50+, and 49+....in a 10.8 mile trip there are 11 stop lights, only half of which are usually red. The speed limits are 35-40. This beats the heck out of our 13-14 mpg Voyager. The only long trip I took it on was 170 miles with the cruise set at 55....maybe four stops and 62.1 mpg. Move to flat Indiana and find an area with good traffic flow.
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