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Daily Eco drive what setting ?

Discussion in 'General Mercedes-Benz Related Discussion' started by SquabzZz, Nov 15, 2012.

  1. SquabzZz

    SquabzZz Senior Member

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    Hey people this being my first merc I still have a bunch of questions to ask!!

    For everyday economical driving what setting should I have the merc in Comfort or Sport ?

    I know the gear changes depend on how your foot is on the throttle but still what setting should I be in ?
     
    Last edited: Nov 16, 2012
  2. paul hayward

    paul hayward Senior Member

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    comfort and a very gentle right foot will help the MPG ...No fun though;)
     
  3. whitenemesis

    whitenemesis Senior Member

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    I have never seen any mpg advantage in either of the settings.

    Save the C for when the going gets slippery and enjoy the S for day to day driving.

    If you want economy, easy on the right foot...
     
  4. television

    television Always remembered RIP

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    Most of use find little difference, C should be the best one for in town work as it is a second gear start
     
  5. OP
    SquabzZz

    SquabzZz Senior Member

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    Sport it is ! Been driving around in comfort all the time lol
     
  6. Troon

    Troon Active Senior Members

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    I always drive in C; S is too frenetic. C does not mean second-gear starts in every car: mine never starts in second.

    You'll see far more significant fuel savings from driving style: looking ahead and avoiding unnecessary changes of speed. Even a perfectly aerodynamic frictionless car will use energy accelerating and deceleration: kinetic energy is ½mv², and that energy comes from fuel and disappears as brake heat (and other heat losses). It matters little where teh shift points are.

    Curiously, it doesn't matter how hard you accelerate either, if you're going to then maintain the speed for a long time (such as on a motorway slip road): the car uses the same energy to get from speed 1 to faster speed 2 whether you spread it out over a long time or give it the beans — provided you don't use wide-open throttle and end up over-fuelling.
     
    Last edited: Nov 16, 2012
  7. Naraic

    Naraic Moderator

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    Interesting. How does a car use energy on deceleration? Especially MB...since with the gearbox engaged and foot off the accelerator...fuel is cut off above a certain road speed?
     
  8. Troon

    Troon Active Senior Members

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    Sorry, poor phrasing on my part. Accelerating, you are converting expensive chemical energy to transient kinetic energy. You then lose it decelerating (converting kinetic energy to heat through friction, whether road, brake or air). Of course, you also expend chemical energy overcoming friction and other losses to maintain a steady speed or to keep the engine turning over at rest.
     
    Last edited: Nov 16, 2012
  9. robparker

    robparker Senior Member Authorised Forum Supporter

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    Although, I have also heard a theory that wide open throttle has less drag against the throttle plate and so is the most efficient use of it, so to accelerate up to a speed you should use open throttle to get there, release and basically keep using open throttle/release(loose speed) open throttle... etc to drive along, as driving with partial throttle is innefficient. No idea what truth there could be to that, plus even if it was, thats a horrible way to have to drive!
     
  10. Troon

    Troon Active Senior Members

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    In a simple engine, WOT or close to it is most thermodynamically efficient: look up "brake specific fuel consumption charts" which are contour maps showing the grammes of fuel needed to produce 1 kWh of energy, plotted against rpm and load. Typical engines are most efficient around the peak torque speed at about 80% load.

    Modern ECUs tend to overfuel at WOT and close to it, to improve performance and cooling at the expense of efficiency.

    So yes, "burning and coasting" is an efficient way to drive if you're in a fuel economy challenge vehicle, like the 8000mpg ones that physically shut off the engine and roll during the coast phase. In a real car, though, other losses would make this much less beneficial and as you say, it's a horrible way to drive.

    The other problem is that modern cars are so over-powered, you can't stay at 80% load for long without losing your licence. This is why range-extended electric vehicles use a small engine, to be able to run it at its optimum point to charge the batteries for minimum fuel expenditure.

    It's a complex subject with diminishing returns. The two key points I practice when driving are:
    • avoid braking as much as possible by looking ahead and anticipating variations in traffic speed, minimizing my own speed changes;
    • remember that wind drag goes up with the square of the speed and that this drag dominates other forces at high speeds: driving at 60 or 70 is much more efficient than at 80 or 90, putting aside the legal aspects.
     
  11. orb the Impaler

    orb the Impaler Senior Member

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    The latter has an amazing difference on my commute to Leeds (M62) every day.

    If I drive in in heavy traffic with quite a bit of stop-start at the Leeds end I get over 63mpg from my SLK.

    Do the same trip at an earlier time and hence spend a lot of time at around 85 this drops to low 50s and as far down as 45mpg. An amazing difference.
     
  12. television

    television Always remembered RIP

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    In Sweden all economy test and runs are done by getting the car into a higher gear as soon as possible, then back off, they do it the same way in Germany, so you are correct from a practical point
     
  13. OP
    SquabzZz

    SquabzZz Senior Member

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    Wow lots of good information but that's not really what I meant oooops

    Just really ment when I'm driving to get as many mpg as possible would it be better in comfort or sport mode but I guess it don't really matter just need careful driving with forward looking
     
  14. mikestrivens

    mikestrivens Senior Member

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    Anticipation is the best form of economy setting.
     
  15. television

    television Always remembered RIP

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    Do you have the 7g box or the 5 speed
     
  16. OP
    SquabzZz

    SquabzZz Senior Member

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    It's a 5 speed auto (don't think it's a 6 speed)

    Has the paddle shift too :cool:
     
  17. television

    television Always remembered RIP

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    If the 722.6 5 speed box, in town use the C it should be marginally better, it will not roll back on hills as well
     
  18. OP
    SquabzZz

    SquabzZz Senior Member

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    Need to actually look into the box as Parkers state there a 5 speed and the HpI I did on the car states its a 6 speed auto lol

    Regardless I love the car
     
  19. television

    television Always remembered RIP

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  20. OP
    SquabzZz

    SquabzZz Senior Member

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    What happened to 6 lol
     

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