Official vs Actual MPG
Discussion
Thought I may as well share this with you as I've been working it out this morning.
Using four very different cars, and a bike that I have owned over the last few years, I have calculated my own MPG, and also used user submitted data courtesy of Fuelly and SpritMonitor, as well as the official figures from Parkers to draw some conclusions.
What I have worked out is that UserSubmitted MPG worked out as 90% of the Official figures in almost all cases.
I also found out that living in the middle of the Hills and enjoying my driving, I almost always get 83% of UserSubmitted MPG and 75% Official MPG.
I didn't expect the results to be so consistent between cars, but the 83% and 90% numbers always work out for the cars I have owned.
Using four very different cars, and a bike that I have owned over the last few years, I have calculated my own MPG, and also used user submitted data courtesy of Fuelly and SpritMonitor, as well as the official figures from Parkers to draw some conclusions.
What I have worked out is that UserSubmitted MPG worked out as 90% of the Official figures in almost all cases.
I also found out that living in the middle of the Hills and enjoying my driving, I almost always get 83% of UserSubmitted MPG and 75% Official MPG.
I didn't expect the results to be so consistent between cars, but the 83% and 90% numbers always work out for the cars I have owned.
That sounds about average, so I think that shows that you've owned very average cars. 
I'm guessing all normally aspirated, fuel injected petrols? Turbos tend to average slightly further from their official figures than that in my experience, and carbs rather better (where they have figures at all).
I'm guessing all normally aspirated, fuel injected petrols? Turbos tend to average slightly further from their official figures than that in my experience, and carbs rather better (where they have figures at all).
Edited by kambites on Wednesday 21st December 12:29
2011 Merc e250 diesel
1997 BMW 328i touring
1997 Nissan Skyline Gts-T - slightly Awkward as pulled back >300bhp, so had to compensate
2003 Toyota Yaris 1.3 Petrol
1995 Jeep Cherokee XJ 4.0 Petrol
I just did the XJ and it worked out the same, so 5 cars now.
As I said, all very different cars!
1997 BMW 328i touring
1997 Nissan Skyline Gts-T - slightly Awkward as pulled back >300bhp, so had to compensate
2003 Toyota Yaris 1.3 Petrol
1995 Jeep Cherokee XJ 4.0 Petrol
I just did the XJ and it worked out the same, so 5 cars now.
As I said, all very different cars!
I started off just looking to see if I could work out what MPG to expect from my next car. But looking at official figures against what people achieve using quite large numbers has been a bit more suprising for me. I expected the numbers to be all over the place for different manufacturers. Of course I have only looked at a few cars, but 90% of the official figure seems to be very common.
There will of course be exceptions, maybe some manufacturers are more truthful, or use a different combined cycle.
What it does tell though, is that I should expect 26.5MPG out of my next car purchase... which I can live with
There will of course be exceptions, maybe some manufacturers are more truthful, or use a different combined cycle.
What it does tell though, is that I should expect 26.5MPG out of my next car purchase... which I can live with
Efbe said:
2011 Merc e250 diesel
1997 BMW 328i touring
1997 Nissan Skyline Gts-T - slightly Awkward as pulled back >300bhp, so had to compensate
2003 Toyota Yaris 1.3 Petrol
1995 Jeep Cherokee XJ 4.0 Petrol
I just did the XJ and it worked out the same, so 5 cars now.
As I said, all very different cars!
bit OT but where bouts in west yorks are you?1997 BMW 328i touring
1997 Nissan Skyline Gts-T - slightly Awkward as pulled back >300bhp, so had to compensate
2003 Toyota Yaris 1.3 Petrol
1995 Jeep Cherokee XJ 4.0 Petrol
I just did the XJ and it worked out the same, so 5 cars now.
As I said, all very different cars!
used to see a white R33 near me when i had mine
Efbe said:
2011 Merc e250 diesel
1997 BMW 328i touring
1997 Nissan Skyline Gts-T - slightly Awkward as pulled back >300bhp, so had to compensate
2003 Toyota Yaris 1.3 Petrol
1995 Jeep Cherokee XJ 4.0 Petrol
I just did the XJ and it worked out the same, so 5 cars now.
As I said, all very different cars!
Different cars, but with the same driver and I suspect driven on pretty much the same roads.1997 BMW 328i touring
1997 Nissan Skyline Gts-T - slightly Awkward as pulled back >300bhp, so had to compensate
2003 Toyota Yaris 1.3 Petrol
1995 Jeep Cherokee XJ 4.0 Petrol
I just did the XJ and it worked out the same, so 5 cars now.
As I said, all very different cars!
Also when looking at mpg figures, you need to have an idea at what you are wanting to know, i.e. it could be what will I get mpg out of it, on the roads I drive on and with my driving style.
- Which is pretty valid and despite being the thing most want to know, is actually pretty hard to actually write down. Because people drive in hugely different manners and on a wide variety of different roads.
Or are you wanting to know if 'x' car is likely to be more fuel efficient than 'y' car? This has nothing to do with how you drive or where you drive. But you need a 'consistent' test. This too is hard and the current system is far from perfect, but it does try and answer this question. It is really then down to the individual to know how they drive and where they drive to apply 'correction' factors to different types of cars.
e.g. a Focus ST might well be able to achieve a higher mpg than a 6.2 litre Corvette under test conditions. But in the real world most are likely to find it easier to achieve higher mpg in the lazy V8.
300bhp/ton said:
But you need a 'consistent' test. This too is hard and the current system is far from perfect, but it does try and answer this question. It is really then down to the individual to know how they drive and where they drive to apply 'correction' factors to different types of cars.
You are quite right, in the end though I need to work out what I will get from a car.the numbers I have to work with are the Official figures, figures from other people and my own figures from past cars.
From this analysis, the official figures seem completely meaningless and have shown much more variation between the other measures, than the other two between themselves. It is because of this I prefer to use other peoples figures as inputted into Fuelly and SpritMonitor.
Wheras I do agree it's 'how' you drive a car, you will also get the effect of the cars personality on the driver and the reasons for the driver purchasing that car affecting the MPG. I find that when I drive a barge, I drive it like one, when I drive a Tuned car, I drive it like I stole it, etc... and it would seem that other people do the same.
edit:
in response to your point about the V8: I completely agree, I drove a 2009 Yaris 1.1 as a courtesy car, and struggled to keep the MPG above 24, despite the official figures being somewhere around 60!
You would actually expect the results to average out for er, average cars.
What that 90% figure is telling you is that on average, the real world drive cycles people do is approx 10% heavier than the drive cycle used to set combined fuel economy. Even for a pretty sporting car (say an M3 etc) in the UK, the time for which you can actually "hammer it" is really pretty limited (by speed limits / traffic / conditions etc) so for most of the time you are simply following the car ahead!
Now there will be some cars where the gap is wider, maybe something like say a Vanquish or Fezza, where they are only driven as weekend cars and hence have less miles to average out any hooning.
What that 90% figure is telling you is that on average, the real world drive cycles people do is approx 10% heavier than the drive cycle used to set combined fuel economy. Even for a pretty sporting car (say an M3 etc) in the UK, the time for which you can actually "hammer it" is really pretty limited (by speed limits / traffic / conditions etc) so for most of the time you are simply following the car ahead!
Now there will be some cars where the gap is wider, maybe something like say a Vanquish or Fezza, where they are only driven as weekend cars and hence have less miles to average out any hooning.
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