A little PH experiment I would like your help with
Discussion
This is an MPG question so if that bores you switch off now.
Obviously where you get manufacturers MPG figures they often bear little relation to your own driving.
Where if find the biggest discrepancy for me is on the 'extra urban' cycle.
Our current family car is a Peugeot 5008 diesel which supposedly does 60 mpg+ extra urban.
WIth these low powered cars I find that above 70 the fuel economy gets horrendously worse. I'd be curious as to what all your cars do at a stead 70 mph, 80 mph and 90 mph.
So in my case against a 62mpg extra urban claim I get 46mpg at a steady 70, 41.5 at a steady 80 and 37 mpg at a steady 90 (measured over about 10 miles)
As an interesting aside, I tested this in my old 996 and the difference between 70 and 90 was only about 2-3 mpg (aerodynamics I assume)
So can we conclude that if you like to go a little faster than you are supposed to on motorways then it is pointless buying a small engine economical car? That's what I want to find out. (I realise Honest John has similar for general driving but I want to know specifically about motorway driving)
Obviously where you get manufacturers MPG figures they often bear little relation to your own driving.
Where if find the biggest discrepancy for me is on the 'extra urban' cycle.
Our current family car is a Peugeot 5008 diesel which supposedly does 60 mpg+ extra urban.
WIth these low powered cars I find that above 70 the fuel economy gets horrendously worse. I'd be curious as to what all your cars do at a stead 70 mph, 80 mph and 90 mph.
So in my case against a 62mpg extra urban claim I get 46mpg at a steady 70, 41.5 at a steady 80 and 37 mpg at a steady 90 (measured over about 10 miles)
As an interesting aside, I tested this in my old 996 and the difference between 70 and 90 was only about 2-3 mpg (aerodynamics I assume)
So can we conclude that if you like to go a little faster than you are supposed to on motorways then it is pointless buying a small engine economical car? That's what I want to find out. (I realise Honest John has similar for general driving but I want to know specifically about motorway driving)
Edited by blindswelledrat on Tuesday 3rd December 13:24
Krikkit said:
The NEDC extra-urban test has a max of 120kph, which you're only at for 10s, the average is about 63kph. So no, at a motorway cruise you won't get anything like extra-urban figures in an un-aerodynamic shape of vehicle, but other cars (with big engines, say) might do better than the test because of the steady cruising without acceleration and/or in a more appropriate gear.
That's what I was wondering and hoping that an array of responses on this might clarify thisPoleDriver said:
It is meant as a comparison of all cars tested under the same conditions so the consumer knows that the results will relate from car to car accurately, it is NOT a true indication of the consumption you will achieve under 'normal' driving conditions.
Yes exactly. I understand why my extra urban figures are so far out, but I wanted to try and find the most economical car for the type of driving I doRobM77 said:
Regarding my BMW, like the OP I can't quite see how 62mpg is possible extra-urban,
SOrry, one of us has missed the point a little there. I think of "extra urban" as being motorway driving?I am referring to motorway driving here if I have used the wrong terminology.
To clarify: Are you saying your 320 does 62 mpg at 70 mpg? Very impressive if so
RobM77 said:
My understanding of 'extra urban' as far as official mpg figures go is that it's a mixture of driving in a non urban setting. The definition will be somewhere on the web, but I think it involves a bit of motorway, a bit of A road, some stop start etc. Generally it defines most of my driving around my local area, but I average about 48mpg for that. I don't think the EU figures allow for 1 lepton B road driving and frequent sideways action though 
I think IM right on this. They are quoted:Urban (local): 40mpg Extra Urban(motorway): 60 mpg and Combined(self explanatory): 48 mpg
mrmr96 said:
. If car A claims 60mpg and car B claims 40mpg then although you're unlikely to achieve EITHER of those figures, you do at least know that car B will be less efficient than car A.
But my whole point is that this might not be the case for brisk drivers. Admittedly in an extreme example it is going to be, but as per my original post at 90 mph I get just over half the manufacturers claimed figure whereas I would bet there are many cars that are theoretically less efficient but which I will get better mpg at those speeds (quite a few have been mentioned above)RobM77 said:
Interesting. Well not 'interesting' as such but an eye opener.A little interesting update for this.
Ive been doing an identical journey lately from High Wycombe to Sheffield in identical traffic and at more or less the same speed (85-90 where possible but up and down from 65-90 depending on traffic)
Ive done it in two different cars:
2011 Peugeot 5008 1.6D. Theoretical mpg 45 urban 65 EU and 55 combined: Pretty consistent return for that journey: 41 mpg
2004 Saab 9-3 aero 2.0t. Theoretical MPG: 25 urban 45 Eu 35 combined: Return 34mpg
Given that the diesel is more expensive the difference is marginal. It's infuriating because the Peugeot was bought for my wife with the sole purpose of it being economical. Definitely not worth the sacrifice with the s
t underpowered engine.
Ive been doing an identical journey lately from High Wycombe to Sheffield in identical traffic and at more or less the same speed (85-90 where possible but up and down from 65-90 depending on traffic)
Ive done it in two different cars:
2011 Peugeot 5008 1.6D. Theoretical mpg 45 urban 65 EU and 55 combined: Pretty consistent return for that journey: 41 mpg
2004 Saab 9-3 aero 2.0t. Theoretical MPG: 25 urban 45 Eu 35 combined: Return 34mpg
Given that the diesel is more expensive the difference is marginal. It's infuriating because the Peugeot was bought for my wife with the sole purpose of it being economical. Definitely not worth the sacrifice with the s
t underpowered engine.Edited by blindswelledrat on Monday 27th January 11:22
Bill said:
It's a big car with a small engine being made to accelerate at speeds the aerodynamics affect. I'm not surprised tbh, but it'd be interesting* to see how they compare at a steady 70mph.
* Not for you, obviously.
I do find it interesting as I would quite like the holy grail of economy for my specific driving.* Not for you, obviously.
Ill do the specific test next time but I think I know the answer.
I reckon at a steady 70 the SAAB may even take it due to the amount of fuel needed for the Peugeot to maintain the speed going uphill on the motorway. Might be wrong- we will see.
What is apparent is that (as someone further up said) it is impossible to maintain a steady speed on a relatively busy motorway for any length of time and that is what kills the Peugeot economy. Sitting at 75 a lorry will overtake and then the 65 mph car in the middle lane will go into your lane. Then the effort of slowing down and then accelerating to 75-80 again afterwards prevents any kind of consistent economical speed.
thatdude said:
My wifes 120d auto (2005, apparently non-DPF which I discovered recently and I am overjoyed) apparently gets a claimed 51 extra-urban, but we see 43, which is in line with mixed.
Urban is about 34, she gets abhout 31. not bad.
I think that sound pretty crap to be honest.Urban is about 34, she gets abhout 31. not bad.
A small car with a small diesel engine and you are getting mid to late thirties on average?
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