1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

70mph 10% more fuel than 50mph

Discussion in 'General Chat' started by Rorifett, Apr 29, 2009.

  1. Rorifett

    Rorifett Well-Known Member

    Joined:
    Mar 23, 2008
    Messages:
    8,753
    Trophy Points:
    166
    Ratings:
    +2,108
    Has anyone else seen these signs on billboards and at petrol stations?
    Basically it states - Think! Driving at 70mph uses 10% more fuel than driving at 50mph!

    Now, what I'm wondering is - If I drive at 90mph, will that use just a further 5% fuel? :D But seriously, what is this supposed to be telling us; drive at 70 cos it's more fuel efficient? For an extra 40% speed it's only 10% fuel... Hmm...

    Can anyone explain? :lease:
  2. Iccz

    Iccz Active Member

    Joined:
    Apr 29, 2008
    Messages:
    24,152
    Trophy Points:
    166
    Ratings:
    +6,741
    Driving at 50 in 6th gear in my car shows worse MPG than about 65ish :D

    I think it means your MPG decreases if you do 70 instead of 50, therefore you would not get as far on a tank as you do less Miles per Gallon
  3. Mr Noble

    Mr Noble Well-Known Member

    Joined:
    Sep 28, 2008
    Messages:
    14,506
    Trophy Points:
    166
    Ratings:
    +2,403
    Cost more petrol to get there but at least you will get there quicker, ideal if your heading to the garage for petrol :D
  4. Dony

    Dony Active Member

    Joined:
    Aug 10, 2006
    Messages:
    11,178
    Trophy Points:
    166
    Ratings:
    +2,743
    I find that the higher my average mph, then the higher my mpg is. If the trip computer is only showing an average mph of about 30, then my mpg is normally 38.7.

    But if my average mph is around 45 (motorway driving), then the average mpg goes up to 45.5.
  5. eric pisch

    eric pisch Member

    Joined:
    Dec 28, 2006
    Messages:
    7,478
    Trophy Points:
    136
    Ratings:
    +764
    The correct speed to drive at is 120mph

    30 second miles, so you divide the time by 2 to get how long it will take you to get there :)

    works even better when your time costs 20 times that of a gallon of fuel
  6. Epicurus

    Epicurus Active Member

    Joined:
    Jan 17, 2006
    Messages:
    2,924
    Trophy Points:
    103
    Ratings:
    +369
    Government economy figures are about as accurate as the 30 year old braking distance figures in the highway code. I've had many different cars and they've all had different speeds at which they are most economic in top gear.
  7. la gran siete

    la gran siete Active Member

    Joined:
    Oct 5, 2003
    Messages:
    23,075
    Trophy Points:
    136
    Ratings:
    +1,311
    I mostly drive at 56 mph.Cant see the point of haring around as one gets there in the end
  8. wormvortex

    wormvortex Member

    Joined:
    May 29, 2005
    Messages:
    5,205
    Trophy Points:
    106
    Ratings:
    +269
    Bet people love you on the motorway :D
  9. eric pisch

    eric pisch Member

    Joined:
    Dec 28, 2006
    Messages:
    7,478
    Trophy Points:
    136
    Ratings:
    +764
    most people are wondering how you get a donkey towing a caravan up to 56 :D
  10. Lee

    Lee Moderator

    Joined:
    Mar 2, 2006
    Messages:
    4,898
    Trophy Points:
    136
    Ratings:
    +1,675
    I've got at least a 10% increase in mpg due to car being in bust mode. Can get to 50mph downhill. :(
  11. mjn

    mjn Active Member

    Joined:
    May 24, 2001
    Messages:
    14,457
    Trophy Points:
    136
    Ratings:
    +1,347
    In the middle lane as well, i bet.
  12. Chrisoldinho

    Chrisoldinho Member

    Joined:
    Feb 7, 2006
    Messages:
    3,440
    Trophy Points:
    106
    Ratings:
    +269
    I've often wondered about the economy figures of cars and how they state driving at 50 mph is most efficient, possibly as a rule of thumb. But like the OP says if it only uses 10% more fuel driving at 70 and you get there 30-40% quicker then who wouldn't?

    It's hardly a compelling arguement.
  13. Ed Selley

    Ed Selley AVF Reviewer

    Joined:
    Jun 26, 2003
    Messages:
    9,478
    Trophy Points:
    136
    Ratings:
    +1,753
    For some cars, I suspect that there might be more than 10% in it. When I was young and stupid I owned a Nissan 200SX and when I was very stupid indeed, I ran out of money and tried to drive it from London to Andover on a gallon and a bit (I failed). I did learn that it was a huge amount more economical at 50-56mph than at 70 because it was off boost at 50 and at least partly on boost by 70. For some six speed diesel cars I suspect it will be much less than 10%.
  14. Kebabhead

    Kebabhead Member

    Joined:
    Mar 7, 2006
    Messages:
    7,150
    Trophy Points:
    133
    Ratings:
    +509

    It all adds particularly if you do a lot of miles and given petrol is creeping up to the £1 a litre mark again
  15. Iccz

    Iccz Active Member

    Joined:
    Apr 29, 2008
    Messages:
    24,152
    Trophy Points:
    166
    Ratings:
    +6,741
    And this is why the Kyoto Protocol will never work.

    At least they're not promoting some of the methods that those loons use when "hypermiling"...

    See more at:
    Hypermiling :: Even without a hybrid car, no more need to compare gas prices

    TRAFFIC WAVE EXPERIMENTS

    http://www.motherjones.com/politics/2007/01/guy-can-get-59-mpg-plain-old-accord-beat-punk
    • Thanks Thanks x 1
  16. Rorifett

    Rorifett Well-Known Member

    Joined:
    Mar 23, 2008
    Messages:
    8,753
    Trophy Points:
    166
    Ratings:
    +2,108
    Crikey, Mr Traffic Waves waffles somewhat doesn't he? Lol he pretty much said his bit in the first paragraph... Three pages later... Lol
  17. Iccz

    Iccz Active Member

    Joined:
    Apr 29, 2008
    Messages:
    24,152
    Trophy Points:
    166
    Ratings:
    +6,741
    :rotfl:

    Yeah I never bothered to read the whole thing, I got bored of him before half way through :p
  18. Rorifett

    Rorifett Well-Known Member

    Joined:
    Mar 23, 2008
    Messages:
    8,753
    Trophy Points:
    166
    Ratings:
    +2,108
    Hehe yup, me too, bored + the fact that wee graphic he had was going for my head!
  19. eric pisch

    eric pisch Member

    Joined:
    Dec 28, 2006
    Messages:
    7,478
    Trophy Points:
    136
    Ratings:
    +764
    And how dangerous is that, kills the power steering, assited brakes, abs, esp etc and if you turn to far will risk setting the steering lock

    also its innaccurate

    modern cars in gear slowing down with the foot of the throtle burn no fuel
  20. mij

    mij Active Member

    Joined:
    Jan 14, 2002
    Messages:
    2,738
    Trophy Points:
    106
    Ratings:
    +295
    Does the engine stop running then?
  21. FZR400RRSP

    FZR400RRSP Well-Known Member

    Joined:
    Mar 5, 2007
    Messages:
    24,817
    Trophy Points:
    166
    Ratings:
    +4,171
    The injectors cut off until the revs drop to a low level, or you re-apply the throttle.
    • Thanks Thanks x 1
  22. mij

    mij Active Member

    Joined:
    Jan 14, 2002
    Messages:
    2,738
    Trophy Points:
    106
    Ratings:
    +295
    That is news to me, so it does effectively stop the engine.
  23. FZR400RRSP

    FZR400RRSP Well-Known Member

    Joined:
    Mar 5, 2007
    Messages:
    24,817
    Trophy Points:
    166
    Ratings:
    +4,171
    Cuts off fuel supply (either completely or reduces it to miniscule levels).
    It's not like switching off your ignition though.

    Edit, to include following from a fuel injection website.

    Fuel is saved while the car is coasting because the car's movement is helping to keep the engine rotating, so less fuel is used for this purpose. Control units on modern cars react to this and reduce or stop fuel flow to the engine.
    • Thanks Thanks x 2
    Last edited: Apr 30, 2009
  24. Rorifett

    Rorifett Well-Known Member

    Joined:
    Mar 23, 2008
    Messages:
    8,753
    Trophy Points:
    166
    Ratings:
    +2,108
    What if you're coasting?
    Hehe darn edits :D :D

    Although when I said coasting I meant with the car out of gear but engine still running, does the above still apply?
  25. FZR400RRSP

    FZR400RRSP Well-Known Member

    Joined:
    Mar 5, 2007
    Messages:
    24,817
    Trophy Points:
    166
    Ratings:
    +4,171
    No, evidently your car will resort to idle speed, in that scenario.
    In which case, you will be using a small amount of fuel.
    So it can often be better to let a car slow down 'in gear' than putting it into neutral.
    One often uses no fuel, one definitely uses some.
    But we're probably talking minute differences, TBH.
    • Thanks Thanks x 1
  26. funkyspider

    funkyspider Active Member

    Joined:
    Jun 7, 2007
    Messages:
    3,214
    Trophy Points:
    106
    Ratings:
    +497
    Given that fact, on a long motorway run you could save probably 20% by driving at 60mph 2feet behind a wagon for the slipstream effect.

    Strange they don't mention that.
  27. Kebabhead

    Kebabhead Member

    Joined:
    Mar 7, 2006
    Messages:
    7,150
    Trophy Points:
    133
    Ratings:
    +509
    Hardly safe driving is it and is worth taking that risk just to save a bit of fuel
  28. FZR400RRSP

    FZR400RRSP Well-Known Member

    Joined:
    Mar 5, 2007
    Messages:
    24,817
    Trophy Points:
    166
    Ratings:
    +4,171
    I swear to god, I used to have a mate did this.
    In his Vauxhall Viva.
    He fitted a vacuum gauge, which gave him a rough idea of fuel consumption.
    He would then drive dangerously close to lorries/buses, all the time revelling in the reading his gauge was giving him.
    That's right, he'd be looking at the gauge as he was 3ft behind a lorry/bus.
    What a pillock.:eek:
  29. Ethics Gradient

    Ethics Gradient New Member

    Joined:
    Jul 29, 2003
    Messages:
    3,680
    Trophy Points:
    0
    Ratings:
    +447
    Driving from Heathrow to Manchester airport at 50 rather than 70 would save you an amazing £2 in fuel ... for an additional 2hrs in the car (using average fuel consumption figures)

    If you commuted 20miles per day on the motoryway to work (10miles each way)
    @50mph you would save yourself a nice £48 a year.
    .... unfortunately that would be at a cost of an extra full 24hrs in the car.
    • Thanks Thanks x 2
  30. Rorifett

    Rorifett Well-Known Member

    Joined:
    Mar 23, 2008
    Messages:
    8,753
    Trophy Points:
    166
    Ratings:
    +2,108
    :D I remember on a Discovery programme, the one with those two annoying twits who prove or disprove theories/ye olden tayles etc who showed that driving in a truck's slip stream had major effect within about 20 feet or so but was negligable (sp?) difference the closer you got, can't quite remember the details - programme was Mythbusters by the way.

    So you basically save 75p on average per hour of your life in your car? Meh, I'll go for driving at 70 hehe

Share This Page