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what speed to achieve best mpg?

Discussion in 'A3/S3/Sportback (8P Chassis)' started by audi_driver, Jun 6, 2008.

  1. audi_driver
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    audi_driver S LINE

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    [Jun 6, 2008]
    i heard 50 mph is better for fuel efficieny than when you are driving 40mph. Can anyone correct me if i am wrong? Also, when is it best to change gears? at 1500 or 2000 or inbetween? Its nice to know because of the fuel rise and i do quite alot of travelling every day.

    Any other tips that might help save fuel will help:D
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  3. xs2man
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    xs2man Member

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    [Jun 6, 2008]
    56 mph used to be the optimum speed that the manufacturers used in order to obtain the best fuel consumption figures. Unsure about the most efficient point to change gear though.

    Make sure your fluid levels are all correct and tyre pressures are correct. You can get supposedly more economic tyres aswell, that supposedly help here. And an economic remap for the engine. I'm sure others will chip in with more advice.
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  4. dsl55
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    dsl55 exploring other avenues

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    [Jun 6, 2008]
    I can't see that 56mph is the best cos surely it depends on how many gears, what gear you're in etc? I could do 56mph in 2nd and not be particularly efficient, likewise if you're going too slow in too high a gear you're bordering on 'flooding' the engine? I would have said that it's the revs that are more important / engine load etc. I may be wrong but mpg at 56mph in 5th will be different to in 6th
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  5. S3 Rav
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    S3 Rav Well-Known Member

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    [Jun 6, 2008]
    i agreee. you can be in 6th doing 56 where your engine is strugling. i find in my 8l s3 that im more economical at 75 then 70 for instance.
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  6. rich1068
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    rich1068 Member

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    [Jun 6, 2008]
    If the OP is after real world improvements I would have said bang on the speed limit for whichever road he's on. As someone else pointed out tyre pressures are important too.
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  7. mfspen
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    mfspen Member

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    [Jun 6, 2008]
    I think the best you can do is to keep the engine on its torque plateau at all times, but not at unnecessarily high revs.

    For my engine, the plateau starts at about 2000rpm, so I find that changing up just below 3000rpm is optimum. When you let the clutch in after changing up, the revs drop to just above 2000rpm. I can get 39mpg on a run from 2.0T in this way, and the performance is still pretty good.
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  8. dummi
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    dummi smoking a6

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    [Jun 6, 2008]
    usually around 2500rpm cruising speed
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  9. audi_driver
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    audi_driver S LINE

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    [Jun 6, 2008]
    I do 50mph on the motorway in 6th gear, so does that mean its wrong to change up to 6th so fast? i tend to change gears around 2000revs
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  10. S3 Rav
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    S3 Rav Well-Known Member

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    [Jun 6, 2008]
    personall i would say 2000 revs is too low because the engine is just strugling then. i usually change at arouns 2500 if i want to save petrol.
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  11. S3 Rav
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    S3 Rav Well-Known Member

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    [Jun 6, 2008]
    but as said before it all depends on different engines, hills etc etc.
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  12. cooni
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    cooni Member

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    [Jun 6, 2008]
    how about on a flat road, no traffic, 6th (or highest) gear?
    what speed/rpm is "ideal" to cruise on in terms of economy?
    #11
  13. benw123
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    benw123 Moderator

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    [Jun 6, 2008]
    Last year, I helped my brother move house and when we returned his hired box-transit van back to the rental company, I followed him from Ipswich to Colchester along the A12 at around 40mph. The computer was showing well over 60mpg when we got there.IIRC, drag increases at the square of speed, so if you do 80mph instead of 50mph - regardless of revs used - you'll reach your destination faster but having spent more fuel in the process. Even dropping your motorway speed to 70mph for the journey would probably make a good difference.Other things to think about (some already mentioned) for better economy are to up the tyre pressures slighty, shut all windows, remove roofboxes, switch off A/C where you can and always use the highest gear possible regardless of speed.
    #12
  14. Amchlolor
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    Amchlolor Active Member

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    [Jun 6, 2008]
    BMW still fit these 'MPG gauges' in the bottom of their speedo (see below, not my speedo)
    I used to question it's usefulness, but it's actually a really good tool.
    Much easier to read, at a glance, than a digital 'DIS' type display.
    Once on the motorway, I can easily see that my car is giving better MPG in 5th, rather than 6th, at speeds under 85mph.
    Without the gauge, you'd just whack it into 6th and 'assume' it was better.
    In normal driving, the needle's all over the place though, which can become annoying.
    You learn to ignore it until you're cruising.
    [​IMG]
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  15. audi_driver
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    audi_driver S LINE

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    [Jun 6, 2008]
    oh, here's another one, when you are driving down a hill, u stop accelerating and just let your car roll down right? what if i put the gear into neutral, does that actually save any fuel?
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  16. rodenal
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    rodenal Active Member

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    [Jun 6, 2008]
    No, as modern engines use minimal fuel under engine breaking
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  17. xs2man
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    xs2man Member

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    [Jun 6, 2008]
    lol. You'll be driving like my grandad then. Should save some fuel, because the engine is under no load and at idle. But I don't think that is the safest way to drive by a long way. In fact, someone once told me this was illegal (but that was a long time ago, and i could be mistaken).

    edit: i stand corrected, and somewhat embarrassed.
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  18. rodenal
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    rodenal Active Member

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    [Jun 6, 2008]
    You're quite right in that it isn't a clever way to drive tho, the car is essentially out of control (albeit not to an extreme extent)

    Dunno about this being illegal tho, for one thing how would you ever tell
    #17
  19. Amchlolor
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    Amchlolor Active Member

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    [Jun 6, 2008]
    No more so than going downhill in an automatic.
    Zero engine braking on an auto, unless you physically select a manual option and change down the gears yourself.
    #18
  20. rodenal
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    rodenal Active Member

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    [Jun 6, 2008]
    But in an auto you're always 'in gear' when in neutral the car is freewheeling which isn't terribly safe.

    I see the point you are making tho, i doubt it's ever caused any serious accidents
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  21. RobB
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    RobB Member

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    [Jun 6, 2008]
    What Car this month have an article about different speeds vs mpg. Worth a quick read but essentially says that from around 40mph, your consumption will rise, and at a non linear rate up to the 100 mph as tested, across a few different types of car. The 56mph (90kph) is a myth.

    They also look at different mpgs in 4th, 5th and 6th to demonstrate that using highest gear possible is best. However, Bowefer, your suggestion that 5th is better than 6th up to 85mph in yours blows this one.
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  22. Amchlolor
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    Amchlolor Active Member

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    [Jun 6, 2008]
    I don't know how they can say this, because it's car-specific.
    Stick my car in 6th, below 85mph, and you have to use much larger throttle openings to keep your speed up, compared with 5th.
    I suppose, in theory, 6th will be 'better', but in the real world, even on a motorway, one is always adjusting the throttle.
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  23. dsl55
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    dsl55 exploring other avenues

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    [Jun 6, 2008]
    not strictly true, depends what sort of clutch type affair they have (sorry, can't remember the proper terminology) but my wife's freelander reverts to 'neutral' under so many revs if you take foot off the gas at 56mph say the revs drop to tickover
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  24. benw123
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    benw123 Moderator

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    [Jun 6, 2008]
    That's probably because sixth gear is much taller, and requires greater throttle to run it.

    It's a bit like riding a bike in high gear - takes much more effort to maintain a similar speed that could be achieved in a lower gear.
    #23
  25. JamS3
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    JamS3 Active Member

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    [Jun 6, 2008]
    Totally agree mate

    Even in my car driving along the motorway in 5th at speeds above gives better economy than 6th gear. Even saw 37mpg on a lazy drive up the motorway the other day (30miles)!!
    #24
  26. bamurphy
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    bamurphy New Member VCDS Map User

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    [Jun 6, 2008]
    **oh, here's another one, when you are driving down a hill, u stop accelerating and just let your car roll down right? what if i put the gear into neutral, does that actually save any fuel?**

    I may be wrong but leaving A3 8P in gear rolling up to lights at revs above 1400rpm uses a negliable amount of petrol?
    #25
  27. marriedblonde
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    marriedblonde Moderator

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    [Jun 6, 2008]
    Not in mine :( Although there is one in Claire ML, the fuel gauge... Cain it and you can see it drop...
    #26
  28. marriedblonde
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    marriedblonde Moderator

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    [Jun 6, 2008]
    No leaving your car in gear shuts off the fuel supply, de-clutch and it needs fuel to keep the engine running.

    J.
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  29. a3mad
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    a3mad New Member

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    [Jun 6, 2008]
    Tips on Filling your Vehicles...
    [FONT=Arial,Arial]This is a Message received from a friend: [/FONT]
    [FONT=Arial,Arial]I don't know what you guys are paying for petrol... but here in Durban, we are also paying higher, up to 47.35 per litre. But my line of work is in petroleum for about 31 years now, so here are some tricks to get more of your money's worth for every litre. [/FONT]
    [FONT=Arial,Arial]Here at the Marian Hill Pipeline, where I work in Durban, we deliver about 4 million litres in a 24-hour period thru the pipeline. [/FONT]
    [FONT=Arial,Arial]One day is diesel; the next day is jet fuel, and petrol, LRP and Unleaded. We have 34-storage tanks here with a total capacity of 16,800,000 litres. [/FONT]
    [FONT=Arial,Arial]ONLY BUY OR FILL UP YOUR CAR OR BIKKIE IN THE EARLY MORNING WHEN THE GROUND TEMPERATURE IS STILL COLD. Remember that all service stations have their storage tanks buried below ground. The colder the ground, the denser the fuel, when it gets warmer petrol expands, so buying in the afternoon or in the evening.... your litre is not exactly a litre. [/FONT]
    [FONT=Arial,Arial]In the petroleum business, the specific gravity and the temperature of the petrol, diesel and jet fuel, ethanol and other petroleum products play an important role. A 1degree rise in temperature is a big deal for this business. But the service stations do not have temperature compensation at the pumps. [/FONT][FONT=Arial,Arial]WHEN YOU'RE FILLING UP, DO NOT SQUEEZE THE TRIGGER OF THE NOZZLE TO A FAST MODE. If you look, you will see that the trigger has three (3) stages: low, [/FONT]middle, and high. In slow mode, you should be pumping on low speed, thereby minimizing the vapours that are created, while you are pumping. All hoses at the pump have a vapour return. If you are pumping on the fast rate, some of the liquid that goes to your tank becomes vapour. Those vapours are being sucked up and back into the underground storage tank so you're getting less worth for your money.
    ONE OF THE MOST IMPORTANT TIPS IS TO FILL UP WHEN YOUR TANK IS HALF FULL. The reason for this is, the more fuel you have in your tank, the less air occupying its empty space. Petrol evaporates faster than you can imagine. Petroleum storage tanks have an internal floating roof. This roof serves as zero clearance between the petrol and the atmosphere, so it minimizes the evaporation.
    Unlike service stations, here where I work, every truck that we load is temperature compensated, so that every litre is actually the exact amount.
    ANOTHER REMINDER, IF THERE IS A FUEL TRUCK PUMPING INTO THE STORAGE TANKS, WHEN YOU STOP TO BUY, DO NOT FILL UP - most likely the petrol/diesel is being stirred up as the fuel is being delivered, and you might pick up some of the dirt that normally settles on the bottom.
    Hope, this will help you get the maximum value for your money.
    DO SHARE THESE TIPS WITH OTHERS! LET’S SHARE INFORMATION AND BENEFIT ALL, FOR THE BETTER OF MANKIND. :applaus:
    ***********************
    #28
  30. Dandle
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    [Jun 6, 2008]
    I personally dont think much of that is true. there may be some truth in it if the fuel was pumped over ground but the fact it states pump in the morning because the ground is colder kind of proves whoever wrote that deosnt know what they are on about. If you dig down about 2-3 ft under ground the temperature doesnt change very much at all even throughout the year, let alone over one day. The fuel tanks are much deeper than that and wont suffer with temperature variation(not enough to be mentionable anyway).
    #29
  31. a3mad
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    a3mad New Member

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    [Jun 6, 2008]
    The best way to achive maximum MPG on motorway driving is to follow an large LGV vehicle close.
    The slip streaming effect is unbeatable.
    All UK Trucks are meant to have a speed limit of 90kph - 56mph +/- 3%.
    Choose a big box trailered one as apposed to a curtainsider sit behind one for a mile and set your cruise control (you have to be very close 1-2 car lengths 'Scary'!!) and what your average MPG rise and rise.
    The truck's slip stream will actually pull your car along and you cruise will shut off fuel supply whilst 'coasting' along.
    I have achived 67MPG on the DIS using this method, although it doesn't do any good for stone chips!!
    Extreme but it works!!
    #30
  32. Phil's Barber
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    Phil's Barber Top Gear

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    [Jun 7, 2008]
    I make you right! I managed 865 miles from a 70 litre tank in my A4 TDI 170 this month.

    56mph is def the best eco-speed for me. This was on new Conti 3s on the correct pressures and sat behind HGVs as much as possible.

    In fact these days I am getting so obsessed with fuel economy that I am seriously considering something very frugal such as a Prius. I have also looked at the Focus ECOnetic. This car claims 65mpg on combined cycle and 115g/km CO2 emissions.

    Audi don't really compete on this front even with the new CR diesels.
    #31
  33. xs2man
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    xs2man Member

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    [Jun 7, 2008]
    The Prius is a lie, lol.

    Its fuel computer lies (probably get the same actual consumption, maybe less, than your A4). It's not a carbon cutting machine (the carbon cost of producing the car in the first place is directly related to the weight, and the prius weighs in at near 2 ton).

    Maybe the Focus is ok, but in a side by side test between the Prius and the Fiat Panda 100 HP, the prius would have to do 1,000,000 miles to offset its orginal carbon cost over the Fiat, so dont buy one to be "green".

    In fact dont buy one full stop. If your already getting that economy out of a nice big saloon car, enjoy the comfort. Man made global warming is a con, and you aint gonna save THAT much on fuel from moving to a less comfortable motor.
    #32
  34. Phil's Barber
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    Phil's Barber Top Gear

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    [Jun 7, 2008]
    I'm not really that fussed about the environmental impact of the car I drive as long as it's not horendous, I am far more concerned with the cost to run it. I hear what you say about the economy I already have but I need to work so hard to get it (slip streams, changing gear at 1800rpm etc) I don't know if I could really bring myself to get behind the wheel of a Prius to be honest but the Focus is a great car. I imagine I will probably end up in something like a 118d/120d (I know, I know!)
    I wish Audi could build a trully refined and economical diesel engine and then design a car that handled and rode well to put it in!
    #33
  35. dummi
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    dummi smoking a6

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    [Jun 7, 2008]
    absolutely spot on. depending how powerful your car is, 2500rpm is around where manufacturers set optimum torque and gears to match drag and predicted speed requirement on the motorway in the overdrive gear

    but slower the better, for example in theory one gear down at 2500rpm would be better, you'll be driving slower but still in the engines most fuel economical rev band. worth giving it a try one day when conditions allow it
    #34
  36. benw123
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    benw123 Moderator

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    [Jun 8, 2008]
    Well I did! Like the quote above, the Prius has attracted a lot of negative press about Toyota's green credential claims, but when it's returning 60mpg+ on my urban commute, who cares?

    Petrol is massively cheaper than diesel at the moment, and I've calculated I'm saving more than £10 a week over the same 25-mile (50 miles daily) commute in and out of West London than I would with my Sportback 2.0TDI. The Prius does struggle a bit on longer runs, but driving down to my parents and back in it today (84 miles each way), it returned an indicated 51mpg, a bit less than the Sportback would.

    As per my previous post, with the Prius the same approach applies - the slower you go, the better the mpg. I would say however that if your driving involves a lot of motorways, something like the Focus or 118d would probably be better. The Prius really shines in the city, where you can keep it in electric mode at speeds under 30mph.
    #35
  37. MJZ 6370
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    MJZ 6370 Member

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    [Jun 8, 2008]
    My 2.0 TFSI is more economical at 80mph than 75 mph according to the DIS! It is strange but true today on the motorway. 70 mph appears to be slightly less efficient.
    #36
  38. audi_driver
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    audi_driver S LINE

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    [Jun 9, 2008]
    Changing from my usual speed of 50mph on the motorway from my daily 20 minute routine, i decided i was going to go 80mph all the way back home since i havent put my foot down in a long while, it just amazes me how much petrol i save driving 50mph after looking at the tank meter. I use to put in at least 50 to 60 pounds worth of petrol every once a week cos my misses always wanted to see me, thank god i sorted that out !
    #37
  39. benw123
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    benw123 Moderator

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    [Jun 9, 2008]
    #38
  40. TFSI
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    TFSI Born to Fish

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    [Jun 9, 2008]
    Fuel economy is down to low revs, high gear within reason and light throttle. Also read the road back off early for obstacles like roundabouts, junctions etc.

    Example = 44ton truck

    0% Throttle = 200 mpg

    100% Throttle = 1.5 mpg

    Good driver average 8.5 mpg

    Bad driver average 5.2 mpg
    #39
  41. Amchlolor
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    Amchlolor Active Member

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    [Jun 9, 2008]
    If sitting behind HGV's is the only way you can afford to run your car, you should definitely consider another car.:tocktock:

    I was driving around in the wife's diesel Clio again yesterday.
    The thing does close to 60mpg and costs £35 to roadtax, yet it's genuinely fun to drive.
    Every time I'm in it, I keep thinking "this is all I need, it really is.."
    I'm lucky enough to be in a position where I get a company D3 but, if I were to leave for a company that gave a car allowance instead, there's no way in hell I would be driving something as flash.
    It would be a small diesel, all the way.
    #40

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