Bad MPG Theory

Discussion in 'Gen 3 Prius Main Forum' started by nparker13, Aug 11, 2009.

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  1. Keep in ECO, forget about the people behind you

    25 vote(s)
    38.5%
  2. Get up to speed, sacrificing MPGs

    32 vote(s)
    49.2%
  3. I dont have a Prius yet, I just like voting for things.

    8 vote(s)
    12.3%
  1. MikeDS

    MikeDS Member

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    So how much acceleration is too much? All things being equal I'd love to just gun it and get up to speed, but I don't want to waste gas doing it. I haven't tested it much because I've been driving like grandma during the break in period. Still only have 425 miles on the car...getting 49.2 according to the computer, but I live in a hilly part of SoCal and do a lot of short trips...I have to say when it dropped from 50 to 49 I was kind bummed, haha...my old car got 17mpg, so I should be happy...haha
     
  2. Mike Dimmick

    Mike Dimmick Active Member

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    The EPA does not test the cars. The manufacturers test the cars. EPA verifies a percentage of new submissions to check that the manufacturers are honest.

    The manufacturers test the cars following the fixed test schedules. These dictate exactly how hard the 'driver' (usually a computer-controlled pedal-pusher) must accelerate and brake to follow those curves. The hardest acceleration on the City test is 3.3mph/sec, which if done as a steady acceleration would take 18.2 seconds to reach 60mph. Most people would consider that very slow acceleration. The High Speed test has a peak of 8.46mph/sec.

    Because it's hard to simulate curves and inclines on a dynamometer, they don't. As a result the results are quite idealised - which is why the raw dyno results are discounted. However, the 2008 tests include some extreme conditions that cannot occur at the same time - A/C use at high temperature, and cold-temperature running - which reduce the results below what many people can achieve with very little effort.

    EPA's tests are at least based on some recorded driving, even if the City test was designed nearly 35 years ago. The EU testing is entirely synthetic, isn't discounted, hasn't been updated for modern accelerations and speeds, doesn't measure A/C use, and doesn't account for cold weather (20°C is a good day over here!) As a result, the 3G Prius - mechanically identical to the US model - gets 72.4mpg (Imperial gallon - 60.3 miles per US gallon) on the EU combined cycle test, at least with 15" wheels. It will be very hard to achieve that!
     
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  3. 32kcolors

    32kcolors Senior Member

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    Thanks for the clarification. So 50 mpg from those and no hypermiling techniques.
     
  4. cossie1600

    cossie1600 Active Member

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    Since the AC is DC powered, the effects of cycling the compressor shouldn't make that much of a difference unless your batteries are depleted. Most of your gas consumption is going to be based on how much load you are putting on the 1.8L. The higher the load, the more gas you use. The ECO mode simply dumbs down your throttle response. Let's say in regular mode, 40% gas pedal pressure is equilvant to opening the throttle 40%. In ECO, they simply make that 20% so you actually have to push down harder to get the same acceleration. This is done to prevent people who are trigger happy and likes to tap the gas pedal.

    Of course the difference is going to be how much assist you are going to get from the traction motor. I believe the other poster is right. In power mode, the electric motor gets more aggressive and therefore gives you a lot more power upon demand
     
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  5. PriusCrazy

    PriusCrazy Blizzard Pearl for Me

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    Hi nparker,

    I had an interesting "revelation" the other day, especially after keeping my eye on the HSI (and the annoyed people on my rear)...

    I drove a 30 mile round trip, mostly in town, heavy traffic, losts of stop-start like I normally would (sort of heavy-footed) without concern for mileage, except I did coast to red lights whenever feasible. The end result: 62 MPG!

    If you give it a try, you may have to set your dash screen to something other than the HSI just to force yourself to consider traffic instead of real-time stats.

    It is refreshing to read someone is actually concerned they may be doing more harm than good poking along in their new toy. Good luck, do some experimenting. I understand how you feel about contributing to road rage.

    PC
     
  6. Philosophe

    Philosophe 2010 Prius owner

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    Not exactly. The electric A/C uses AC current generated by the inverter from the high-voltage DC.

    Also, there is no A/C cycling as in a regular car, it is of variable speed. Its speed is adjusted dynamically in response to the level of coldness requested (it does not make very cold air then warm it with the heater to the requested temp as it does on a "regular" car). See this thread for more on this.

    ECO mode does throttle down the speed of the A/C compressor, hence limiting the amount of electricity spent by it.

    About the way ECO, normal and PWR mode affect the gas pedal, see the graph at the end of this page (made by hobbit, from PriusChat).
     
  7. cpatch

    cpatch New Member

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    I'm with Jimbo...unless there's nobody behind me I'll accelerate as quickly as I need to in order to keep with the flow of traffic, changing from ECO to PWR mode if necessary (and sometimes just for fun to surprise the guy next to me who obviously rolls his eyes when he sees the Prius). Once I'm at speed I take full advantage of ECO as long as it's not inconveniencing the driver behind me too much. I also drive in the righthand lane a lot more than I use to!
     
  8. AlexT

    AlexT Junior Member

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    I have a Prius IV and the first few weeks used Eco mode to get around Orlando, my work commute is 6.3mi one way on a 35 - 50mph divided street with stop lights. My observations is that Eco when turned on does slow down the A/C fan setting, and deadens the pedal response. I use the normal mode now and watch the hybrid system indicator now and find my fuel ecomomy is better from 52mpg to 60mpg. I noticed leaving the A/C off does more for my fuel economy than the mode switch ever did. I accelerate in both modes at about 80% - 90% of the Eco bar and try not to stay in the red (power) area too long regardless of the mode. I have found out that my mileage is better by anticipating traffic, coasting to lights, accelerating (pulse) and gliding instead of having a steady foot on the pedal. I think the mode switches are more of a gimmick and your mileage will depend more on your driving habits/technique, distance traveled, and speed your traveling. Oh I also keep 42/39psi (f/r) in the tires.
     
  9. denverkam

    denverkam New Member

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    I also was bummed when I dropped below 50, since other folks talk about getting 55 and higher. But I also do a lot of short trips, requiring extra fuel in the couple minutes of warm-up when the ICE just stays on continuously. And I have few long stretches to savor the 100+ mpg glides. I've read many of the posts about how to drive a Prius and feel fairly confident I understand the car. So those of getting under 50 don't need to get too depressed if our driving circumstances don't allow us to maximize the car's potential.
     
  10. cnschult

    cnschult Active Member

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    instead of stupid ECO & PWR buttons way out of convenient reach of the driver I'd like a toggle switch right there on the steering wheel.

    toggle Up: EV mode
    toggle center: normal hybrid mode
    toggle down: ICE mode

    an ICE mode would be really handy when you know the engine is about to kick off but you know it will kick right back on because the light is just about to turn green, the wear & tear is just not worth the engine kicking off for a fraction of a second, it'd be nice to be able to override the engine for turning off for such a short period of time.

    an ICE mode would also be handy in the rocky mountains to force a full battery charge as you approach a steep mountain climb.

    an ICE mode would also be handy in freezing temperature to prevent the engine for shutting off for a fraction of a second when it just makes more sense to override it to stay on.
     
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