I totally ignore the combined figure as this in no way represents the journeys I undertake.
I'm either in built up areas or on the motorway so urban and high speed figures matter to me. In both the A3 2.0TDi 170 and the Aygo we get close to published figures for both scenarios.
As the OP mentioned find an owners club website as these provide more useful data.
"m'way driving should exceed the combined figure quite easily"
Combined figure is always the highest of the three figures, I doubt getting better than this at motorway speeds is possible. For the A3 it's 57 mpg, there is no way I could get this at 70 mph.
I saw some of 5th Gear last night and they are carrying out a test of actual consumption of the Polo Bluemotion which is supposed to achieve mid 70s mpg.
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daveyjp - the combined is always the middle figure as it's always just a weighted average of the other two. No high speed figure is published although the 75mph figure did at one time.
I use the combined figure as that's what I get out of cars, on a long term average - sometimes it drops to the urban figure, sometimes it's almost up to the extra-urban.
Everyone drives differently, in a different mix of traffic and roads.
The whole point of official figures is to allow comparison between models - use whichever of the three conditions is nearest to your actual.
THere is no "supposed to get x mpg"
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I've never owned a car that couldn't get within 5% of the Combined figure. Granted in my normal driving, it's more like 10%, but that's my driving style and conditions. The car is at least capable of matching, or very nearly matching the claimed figure - it's my choice not to drive it in a way that allows this.
As Number_Cruncher and RT said, it's an inexact science with an incredible number of variables . No two people drive the same car in the same spec with the same load and the same maintenance history in the same way on the same roads with the same tyre pressures in the same traffic conditions in the same atmospheric pressure and ambient temperature conditions with the same blend of fuel at the same time. The figures provide a useful comparison guide using a known set of test conditions, but cannot be expected to replicate even a fraction of the possible combinations of the above conditions. Therefore they cannot be taken as any form of useful guide in how much fuel a car will use in your day to day motoring with your combination of the variables above.
It's the same with CO2 emissions. Anyone who thinks that their Prius is emitting its claimed 104 g/km of CO2 when doing 110 mph in lane 3 of the motorway is kidding themselves. Emissions are a function of the amount of fuel burned - more fuel = more emissions. All of these figures are comparative guides only with only a coincidental relationship with the real world.
In my experience, cars I've owned are physically capable of achieving the combined figure if lightly laden and driven very gently in the kind of traffic conditions that the SE only sees on Christmas Day and at 6:00 on a Sunday morning. But they are capable of it nonetheless My rule of thumb is that for normal driving - knock 10% off and I get a reasonably accurate figure from the official combined figure. Based on my combination of those variables (and probably loads of others I haven't listed).
Cheers
DP
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I too seem to get close to the official figures, quite often exceeding them in a C180 auto Coupe. 38mpg for what it's worth on a 'combined-type' run. Usually around 24-26 in town.
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I have, on several occasions, over one or more tankfuls, achieved considerably better MPG figures than officially quoted.
These occasions were very long, easy 50 mph drives on deserted roads abroad. Some friends and I once got more than 1000 miles on one tank (brim to brim) from a Discovery TDi (~47 MPG IMP) in Algeria.
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It is concerning that some cars seem capable of hitting the number (my MB and our Jazz both can) but others are way out (our 1.2 Ibiza can't get anywhere near).
It is known that manufacturers do supply "golden" samples though, and the cars run on thin oil etc. Obviously the manufacturers will set up engine computers to give the best possible results - cars are tweaked to do well in the test (like BMW's latest X5 3.0d).
Auto Express did a study on this with a Ford Focus - it's a emissions thing really, as they don't measure fuel consumption, it's calculated from the CO2 output. Auto Express found the Focus should really be 2 groups higher than it is.
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When considering mpg I always take a loose view. If the "official" figure is less than 30mpg it will be thirsty. If it is supposed to return 30-40mpg then it will be sort of acceptable and if it officially is reputed to do over 40mpg it will be relatively frugal. Beyond that it is really all about how you drive it and under what conditions. I just think of it like this...Wallet pain factor.
Category a ( 40mpg ) = Dull ache!
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Not sure if it answers the question or not but my cars achieve the following:-
Golf - 52mpg quoted combined, 54mpg achieved (brim to brim over 475miles)
Shogun - 26.9mpg quoted combined, 22mpg achieved (mix of motorway and A roads)
Seems to be similar to what others on here are saying really.... I don't like the 22mpg though!
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By the same token my car history...
Citroen Xsara 2.0HDi - 46.2mpg achieved, 54.2mpg claimed - average over 8k
Golf TDI Auto (90Hp) - 34.6mpg achieved, 46.4mpg claimed - average over 4k
Audi A3 2.0TDI (140) - 49.2mpg achieved, 51.4mpg claimed - average over 46k
Audi TT 2.0T FSI - 38.4mpg achieved, 36.7mpg claimed - average over 6k
Seems the powerful cars get closer than less overpowered cars. Just about all these cars were driven in the same mix of driving roughly 25% town/50% motorway/25% backroads, though when I owned the Xsara I lived in the South East.
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.......The official combined figure for the 1.1 Picanto is 53.3 mpg so the owner you mention is getting roughly what the figures suggest they should be getting, so whats your point?.....
The mpg was obtained 'mostly motorway miles', hence the reference to the 64mpg claim.
I accept that the customer would like a basis upon which to form an opinion of a car. In this day and age, fuel economy I suggest tends to sit somewhat higher up the list of desirable factors for private purchasers than perhaps it did even 5 years ago.
My main point was that the official figures often bear no relation to what the actual vehicle is likely to return in real life and that the variance can be enormous. The complication is that the variance between different models, let alone manufacturers, is not constant. I.e. Vehicle 'A' is rated at 50mpg but in real life returns 32mpg; Vehicle 'B' is rated at 42mpg but actually returns 36mpg. Assuming all other aspects are equal eg number of seats, suitability for you and the purpose for which the vehicle will be used, etc etc, which vehicle would attract most interest from the paying public (aesthetics apart).
Some contributors to this thread have already alluded to this fact insofar as some makes/models achieve figures close to published data or acceptably close to it; while others appear to fail miserably. There appears to be no rhyme nor reason, especially when the differences are highlighted by the same driver.
Apart from the internet (as not everybody has access to a computer) where can you find comprehensive independent advice on vehicle mpg and long-term running costs?
Edited by Dynamic Dave on 30/01/2008 at 00:55
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The point of the official figures is to give a basis for comparison on a level playing field.
The variation in economy can be as much about the owner as the car and unless everyone drives the exact same way there can be huge variations - I know people with the same Rover diesel as I have and only get low 40's where I get low 50's - same engine/bodyshell.
And those drivers who 'think' they are driving economically may well not be.
Motorway driving is usually at 70 plus where as best economy is usually a steady 50-60, but at the normal speed the economy will be very different as it could be up to 20 mph difference, thats why 64 mpg wouldnt be reached - the 64 mpg is NOT for motorway driving unless u go very slowly.
It is true however that the way the tests pan out means that the conditions favour some cars more than others with things such as gearing - my Rover 420D has an extra Urban figure of 72 mpg and a combined figure of 53 mpg which is because the car happens to have a high 5th gear and at 50 odd mph the turbo is just coming in but its still barely ticking over, so its the ideal conditions for that particular model. However, speed up and the economy drops noticeably.
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The official EC test figures are as independent as you'll get - they aren't perfect, nothing is.
Actual fuel returns vary widely. No individuals or journalists have so far established that any one manufacturer or model has false results.
Impossible to quantify but model purchase is often stereotypical - meaning that small cars are frequently used for urban journeys while medium cars are often on motorway duty - so don't expect a Kia Picanto to achieve the same % of EC figures as a Ford Mondeo.
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I have usually found that at sensible, consistent mway cruising (around 70ish) I will match the Combined figure......until I got my current 307 (2.0 HDi) which comes nowhere close! I struggle to get 45mpg from that thing.
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As someone who was concerned with emissions and fuel-consumption for more years than I like to remember,I would be interested in where your info on "golden samples" and "thin oil" comes from.The test authorities-all tests are Government observed-can and do check the cars and their engines-so no thin oil or special tyres and they can and do check that the cars can be driven normally both hot and cold.They also check production samples(random) to ensure that they are to the same specification as originally homologated.
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One thing that occurs to me is that laboratory testing cannot account for wind resistance. If 2 cars were tested and gave the same extra-urban fuel consumption but one was a big MPV and the other a low built sports car, then in the real world surely the MPV would give much worse consumption due to its much greater frontal area and generally worse aerodynamics.
I've monitored fuel consumption for 10 years, on our last 4 cars and found I got between 10 and 15% better than the combined consumption figures, but as others reported, could only exceed the Extra-Urban consumption during gentle touring and then not in hilly areas.
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Quite agree jc2. I was also involved for a few years in component test and sign off for EEC, FMVSS and ADR. The guys in the next door office did fuel consumption, crash test etc. The method of obtaining manufacturer's official fuel consumption figures is clearly described in an ECE regulation (#84 if I remember correctly). The vehicle has to be to manufacturer's stated specification (as typically described in driver's handbook).
> laboratory testing cannot account for wind resistance.
That is why the tests are done on a test track or e.g. a motorway in Spain. Wind speed and direction also closely monitored.
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The "road-loads" used for emission and fuel consumption are also observed by government authorities both when originally recorded and when transferred into the dynamometer for laboratory testing.EEC directives & ECE regulations both cover the set-up and testing.
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After a bit of Googling I came across this
www.vca.gov.uk/fcb/faqs-fuel-consumptio.asp
Quote:
My vehicle does not produce the same fuel consumption figures as shown in the 'New Car Fuel Consumption and Emission Figures' publication and/or the Internet site?
Because of the need to maintain strict comparability of results achieved by the standard tests they cannot be fully representative of real-life driving conditions. Firstly, it is not practicable to test each individual new car; thus only one production car is tested as being representative of the model and may therefore produce a better or worse result than another similar vehicle. Secondly, there are infinite variations in driving styles and in road, car and weather conditions, all of which can have a bearing on the results achieved. For these reasons the consumption achieved on the road will not necessarily accord with the official test results.
I appreciate that the official fuel consumption figures are obtained under controlled test conditions and as such may not be fully representative of real-life driving conditions. However, I am concerned that the figures achieved by my vehicle are radically different to the official figures?
You should refer to the 'Hints for Less Environmental Damage' outlined on the VCA website at
www.vcacarfueldata.org.uk/information/hints-for-le...p (links to another site) which outline ways of optimising fuel economy. If, following observation of the recommended points, fuel consumption remains higher than you would expect this may indicate a fault with your vehicle and you should ask an authorised dealer or other competent organisation to examine it.
How is the fuel consumption test conducted?
The test is outlined in Directive 93/116/EC as amended by 1999/100/EC and provides results that are more than representative of actual average on-road fuel consumption than previous tests. There are two parts: an urban and an extra-urban cycle. The cars tested have to be run-in and must have been driven for at least 1,800 miles (3,000 kilometres) before testing.
Urban Cycle
The urban test cycle is carried out in a laboratory at an ambient temperature of 20oC to 30oC on a rolling road from a cold start, i.e. the engine has not run for several hours. The cycle consists of a series of accelerations, steady speeds, decelerating and idling. Maximum speed is 31mph (50km/h), average speed 12mph (19km/h) and the distance covered is 2.5 miles (4km).
Extra-Urban Cycle
This cycle is conducted immediately following the urban cycle and consists of roughly half steady-speed driving and the remainder accelerations, decelerations, and some idling. Maximum speed is 75mph (120km/h), average speed is 39mph (63 km/h) and the distance covered is 4.3miles (7km).
Combined Fuel Consumption Figure
The combined figure presented is for the urban and extra-urban cycle together. It is therefore an average of the two parts of the test, weighted by the distances covered in each part.
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>>cannot account for wind resistance.
Just to expand on Billy Whizz's and jc2's points - yes it can and does account for wind resistance.
The frontal area of the car, and the drag co-efficient of the car are measured, and this is added as an extra speed dependent resistance on the dynamometer rollers.
To make the fundamental point again (as it's clearly passed many people by), the tests are to enable car A to be compared with car B. Comparing the test results with what you actually achieve is meaningless. The test methods provide a carefully controlled level playing field - nothing more! The test can't ever conform to all types of vehicle usage, and that's not their purpose.
Of course, once the test is defined, manufacturers will optimise their vehicle designs to perform well in the tests (q.v. Renault in NCAP tests).
Number_Cruncher
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>That is why the tests are done on a test track
It seems this is old skool and now, as jc2 says, the tests are carried out in the lab with a scientifically accurate compensation for resistance.
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Among the many things I don't know about emissions testing is how the mass of the vehicle is corrected for.
Are weights attached to the rollers to make the rollers up to the correct equivalent rotary inertia?
or
Is there extra load applied to the rollers dependent upon the acceleration?
I've seen some dynamometers at the Brush works which had very large rollers, and the provision for adding masses, but I don't think these are all that common.
Number_Cruncher
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N_C, Couldn't it be done electro-magnetically? (I've used them but don't know the first thing about them).
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>>electro-magnetically?
Yes, I'm fairly sure it could be - I'm just not sure if it is done that way, or by using weights.
Number_Cruncher
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Original dynamometers were water brakes and used flywheels on their own for the inertia;the load being adjusted by the setting of the water brake.Modern dynos use a combination of flywheels and electric simulation.There have been other types using no flywheels and doing it all by electric simulation but these were not common and have dropped out of use.
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