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Model specific boards => Golf mk7 => Golf mk7 GTD/TDI => Topic started by: Sootchucker on 23 June 2015, 07:47
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Right, it's coming up to 2 years since I took delivery of the GTD, and I like the car as much today as I did the day I picked her up (and that's from someone who usually gets bored after 18 months or so).
Just thought I'd ask this question of other fellow devils juice drivers. I've driven the car now for over 15,000 miles in a variety of conditions, (urban, motorway, country lane, Scottish highlands etc), and not once has my MPG ever dipped below 39.3 mpg (and only once due to major road works and traffic jams that week), but overall, for 15,000 miles my average (according to fuelly) is 45.9mpg with a highest of nearly 60mpg (true MPG calculated though litres used at fill up). I'm quite impressed at that considering I've only had about 4 or 5 decent trips in that time with all the others being conducted in my normal rush hour commute to work (though a fairly large town centre), and the journey as described below for my route home - so quite a mix with urban roads being predominant.
So I know the GTD is capable of very impressive MPG figures, even more impressive as mine is a DSG version, but I've been conducting a test over the last few weeks and have come to the conclusion that the GTD (maybe all MK7's ?), are very sensitive to speed as far as economy goes. For instance, on my normal journey home (whilst is about 16 miles of motorway, dual carriageway and urban back streets, providing the route is clear, I can easily top 60mpg (best was 65.4 indicated) if I travel on the motorway and dual carriage way part at 55mph ish. At 60-65mph, that figure drops to about 54-58mpg. At 70-75mph, it drops to about 50 ish and at 80, it's mid forties.
All test done in "normal" mode, with the DSG gearbox in drive mode (not sport), and conducted at least 2-3 times at each speed to get a sort of average over the 2 weeks or so. Obviously far from scientific, but it seemed fairly repeatable.
So I find if I travel at around 65mph, I can usually get around 5-6mpg better than travelling 5mph faster at 70.
Now I'm not complaining, a warmish hatch with over 180hp (and an automatic box) that will still return over 40mpg at 80+ or around 50mpg at 70ish, is pretty respectable in my book, it's just that I don't remember any of my previous diesel VW's ever being so speed sensitive, with such a marked drop off at every 5mph increase increments.
Anyone else noticed this ?
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Yes I find my car (manual) does better MPG at around 50-60MPH exactly as your describing, once I get on the motorway @ 70 mph it drops to low 50s.
Still impressive though, can't wait to get my DSG now :smiley:
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It's the same for all cars (to a greater or lesser extent) depending on things like drag co-efficient and frontal area.
In simple terms, drag increases in relation to the square of speed...
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I agree with Cossieian - but I'm not complaining. With 23,000 miles in 19 months of spirited driving with Winter Tyres on for 2 Winters which does bring the mpg down with the extra tread I'm showing 48.3 life mpg.
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I still love my GTD, MPG is great, looks are great..only negative for me is the excessive tyre wear but nobody's perfect.
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In simple terms, drag increases in relation to the square of speed...
^^^word!
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Although having said that, its also to do with the RPM required for the speed.
You'd probably find the same result if you compared different speeds in 4th at the same RPM differences, albeit that without the extra speed/drag the differences would be less, but still predictable.
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Thanks for stating the obvious guys :laugh: :laugh: I sorta knew that going faster would use more fuel (lol)
What I meant was the penalty (if we call it that), for going over say 70mph, seems greater in the GTD than in my Scirocco or MK5 Golf GTD, whose MPG would only be affected slightly (2 or 3 at most) up to say mid to high seventies MPH, and would only present a real MPG penalty when doing speeds over 80mpg (which of course I never do :whistle:)
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I've noticed the same as you. I thought maybe the drag coefficients or weights would be the culprits but no, the Mk7 has the best drag coefficient out of the the Mk5, Scirroco and Mk7 and weighs less than the Mk5. Think the Scirroco weighs about the same as the Mk7? Not sure.
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Well, then its the gearing for sure then :)
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Never brake, hauling the weight up to speed is a juice slurper.
Also avoid boosting too much. Somewhere on the internet there will be a rpm, AFR graph no doubt.
As others have said. Drag is a drag init. Lowering helps!
:smiley:
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Well, then its the gearing for sure then :)
Closer and more ratios help.
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I guess that's why a 10 speed DSG has been rumoured. Better acceleration :smiley: too and/or smaller engines. Makes you wonder what manual option they will offer against a 10 speed auto - if anything... :sad:
Neil.
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10 speed DSG will be more fuel/CO2 efficient for sure, however the top gear will always be set to whatever they consider to be the "typical maximum cruising speed" at whatever the most fuel efficient RPM value is (probably sub-boost RPM - I seem to remember that typically 70mph is about 1.5k RPM in 6th - thats probably around the sub-boost rev limit).
It seems unlikely that say 8th gear will be for 70mph and 9th and 10th are for effeciency at 80 and 90mph (for example)
What I would hope from 10 speed DSG though is that DSG will return the same CO2 figure as manual in the "approved test"... and thats all VAG actually care about!
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If the engines get smaller and possibly less powerful due to having 10 gears to play with then a six gear Mt would be far less flexible...
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I've noticed the same as you. I thought maybe the drag coefficients or weights would be the culprits but no, the Mk7 has the best drag coefficient out of the the Mk5, Scirroco and Mk7 and weighs less than the Mk5. Think the Scirroco weighs about the same as the Mk7? Not sure.
Other factor is frontal area (Scirocco the smallest)? Mass makes no difference at a constant speed
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If you like a bit of light(ish) physics try:
http://realworldnumbers.com/drag-crisis-the-coefficient-of-drag-is-not-a-constant/
Or this quite easy to read one which is talking about car fuel economy vs speed:
http://www.wired.com/2011/04/what-will-an-85-mph-speed-limit-do-to-your-mileage/
Although I suspect in a GTD and the speeds we are talking about it more to do with the boost being on than anything else.
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You would have to assume that if manufacturers didn't have to maximise fuel consumption at set speeds for comparison purposes then some could actually be really innovative and build really economical ( and maybe performant) engines that were better than figures at the prescribed speeds.
Cheers, Neil