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I joined this forum to find out what 'real life' fuel consumption people were getting from the PB Manual Challenger, as this was an important factor for me in deciding to order one, which hopefully will arrive in the next month.
I found that many people were annoyed at not being able to achieve anything like the 'official' fuel consumption, in some cases (actually incorrectly) blaming Mitsubishi for making false claims. Mitsubishi makes no such claim, so there is no point blaming Mitsibishi.
As I have always been interested in fuel efficiency, I researched exactly how the 'official' figures are obtained, and have a copy of the (68 page) Australian Standard Testing procedure sitting in front of me as I write. I found it interesting to learn how the testing is done, and why it is near useless, and thought others may be interested.
The aims of the Australian Standard fuel consumption testing are noble, to provide a scientifically robust method of fuel consumption testing that is immune from uncontrolled real world variables such as driving style, winds, temperature, hills etc. For that reason, the tests are NOT performed by driving the vehicle in the real world, on roads. So far, so good ....
The tests are performed in the laboratory, on a rolling chassis dynonometer. The car is 'driven' on the dyno by a human driver, according to a standard 'course', namely the standard 'Urban Cycle' course, followed by the 'Extra Urban' course. A brief description of these test cycles :-
While performing the test, the human driver has a speedometer display with two needles, one is the car's actual speed, and the other is the desired speed, as required by the test standard. The driver controls the 'speed' of the vehicle just as he would an the road, using the accelerator, brake, and gears (if manual), while at all times attempting to keep the two speedometer needles coincident, that is, keeping the actual vehicle speed the same as the desired speed set by the standard. The dynonometer has been previously programmed to simulate the vehicle mass, and the wind drag - more about that later. In practice the result will be variable, because of the very short length of course (4km for Urban cycle), combined with the varying ability of the driver to exactly follow the course, and personal choice of the gear shift points in the case on manual transmission. Nonetheless, the dyno test drive can be repeated and the results averaged, to give a reasonably consistent result. So far, so good ....
In reality, it is an observed fact that the Australian Standard results obtained in this way, the same results that are on the windscreen sticker of every new car, are consistently optimistic compared to the fuel consumption actually obtained in the real world. I personally find that extremely annoying, and inexcusable. The 'Official" numbers are useful for comparing the fuel consumption of competing vehicles, but a complete load of rubbish for estimating what fuel consumption the average driver will actually obtain. The fact is, the standard test results are consistently optimistic, but WHY??? There are at least 3 reasons.
(1) Apparently in the interests of international standardization, Australia has chosen to use standard Euro Urban and Extra Urban test cycles, which unfortunately bear little resemblence to driving conditions in Australia. For example, Australia is sparsely populated, so our highway driving, on both major highways and country roads, consists of travelling large distances, at constant speeds of between 90 and 110 km/hr. You might therefore expect (or at least hope!) that the standard Australian Government fuel consumption testing would include a result that reflects this type of driving. Unfortunately not. The closest we get is the Extra Urban cycle, at an average speed of only 63 km/hr !!!!! Well, derr, how many of us in Australia travel at an average speed of 63km/hr on the highway!! Sure, if we travelled at 63km/hr on the highway, then we might conceivably obtain the rated Extra Urban consumption figures, well, so what. What bureaucratic idiot decided that international standardization was more important than producing a result that was actually useful? Yes, I find this sort of BS annoying. It would not be particularly difficult to define an Australin Highway Cycle, giving a result that, on average, actually reflects what highway consumption can be expected. Same deal with the city test cycle, which apparently simulates driving in peak hour in the middle of Paris, at a maximum of 50 km/hr, and an average speed of 19 km/hr. Even if you live in Sydney or Melbourne, I find it hard to believe that you clock up most of your city miles never exceeding 50 km/hr, and at an average of 19km/hr. What utter BS.
(2) Even if we adopted (or at least included) Australian Test Cycles, the errors in the Laboratory test measurements are significant. Despite what the standards people might admit, the main advantage of the Lab based Dyno measurement method is that the measurements can be done quickly and cheaply. Overall, this is still probably the only practical method, but it is certainly not free from errors. While the method avoids some errors associated with real-world driving, it adds many others. Firstly, the test cycles are obviously too short to provide a reasonable simulation of the real world. If you could eliminate all errors and spurious variable in real-world economy testing on the road, I'm sure no one would would even contemplate driving only 4km (as in the Urban cycle), and then claim that those 4km could reasonably represent city driving. Unfortunately, driving longer distances on a dyno is not practical. The next problem is that so many key variable, such as wind drag, have to be accounted for indirectly, resulting in significant errors that inherently don't occur in the first place with on-road testing. For example, I am very familiar with the 'coast down' method that is used for measuring wind drag at a given speed. It's actually not easy to do accurately, and this is one of many such cumulative errors inherent in the dyno approach. The experimentally determined wind drag, mass etc are then programmed into the dyno, which then adds further cumulative errors, for the dyno cannot simulate mass and drag with perfect precision, even if the variables are were known with perfect accuracy. Another potential issue, is that on the dyno, the vehicle is not actually moving through the air, even though the air drag is simulated at the drive rollers. Large fans are used to force air over the front of the vehicle to keep the engine cool, but it is not practical to provide an air blast over the entire front of the vehicle of 100km/hr, for example. This, in turn means that it is impossible to properly simulate the engine temperature under sustained highway conditions, and there could also be a difference due to a different 'ram effect' at the air intake. OK, so you get the idea. The dyno test approach simply swaps some of the errors of on-road testing for other errors, with the result that the published fuel consumption figures can only be taken as an approximate guide, even if we had proper Australian test cycles.
(3) Apart from irrelevant Euro test cycles, I would expect the published fuel consumption figures to be suspiciously optimistic anyway, because much of the key data required for the dyno testing is supplied by the manufacturers. The Australian Standards department simply does not have the resources to measure all the required variables for the dyno testing. For example, the manufacturer would normally provide the wind drag data, plus a lot of other data as well that gets fed into the dyno, or into the complex mathematical analysis that finally yields the fuel consumtion number. Now, I won't go as far to say that the manufacturers are blatantly dishonest (though some may be) but it seems inevitable to me that the data provided by the manufacturers will be as best-case and optimistic as it is possible to be without actually lying, and there is considerable scope for this given that much of the key data (eg wind drag) is experimentally derived. I'll also bite my bum if the vehicle used for the dyno testing is randomly taken from the production line - you can be sure they choose a 'good' one.
For all these reasons, the official Australian Green Guide fuel consumption figures are inaccurate, and invariably optimistic. With reasonable care, anyone can produce measured fuel consumption results that are both more relevant and more accurate that the 'official' figures.
I found that many people were annoyed at not being able to achieve anything like the 'official' fuel consumption, in some cases (actually incorrectly) blaming Mitsubishi for making false claims. Mitsubishi makes no such claim, so there is no point blaming Mitsibishi.
As I have always been interested in fuel efficiency, I researched exactly how the 'official' figures are obtained, and have a copy of the (68 page) Australian Standard Testing procedure sitting in front of me as I write. I found it interesting to learn how the testing is done, and why it is near useless, and thought others may be interested.
The aims of the Australian Standard fuel consumption testing are noble, to provide a scientifically robust method of fuel consumption testing that is immune from uncontrolled real world variables such as driving style, winds, temperature, hills etc. For that reason, the tests are NOT performed by driving the vehicle in the real world, on roads. So far, so good ....
The tests are performed in the laboratory, on a rolling chassis dynonometer. The car is 'driven' on the dyno by a human driver, according to a standard 'course', namely the standard 'Urban Cycle' course, followed by the 'Extra Urban' course. A brief description of these test cycles :-
- Urban fuel consumption defined as: 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, decelerations and idling. Maximum speed is 31mph (50 km/h), average speed 12 mph (19 km/h) and the distance covered is 2.5 miles (4 km).
- Extra-urban fuel consumption defined as: The extra-urban cycle is conducted immediately following the urban cycle and consists roughly half steady-speed driving and the remainder accelerations, decelerations and some idling. Maximum speed is 75mph (120 km/h), average speed is 39mph (63 km/h) and the distance covered is 4.3 miles (7 km).
While performing the test, the human driver has a speedometer display with two needles, one is the car's actual speed, and the other is the desired speed, as required by the test standard. The driver controls the 'speed' of the vehicle just as he would an the road, using the accelerator, brake, and gears (if manual), while at all times attempting to keep the two speedometer needles coincident, that is, keeping the actual vehicle speed the same as the desired speed set by the standard. The dynonometer has been previously programmed to simulate the vehicle mass, and the wind drag - more about that later. In practice the result will be variable, because of the very short length of course (4km for Urban cycle), combined with the varying ability of the driver to exactly follow the course, and personal choice of the gear shift points in the case on manual transmission. Nonetheless, the dyno test drive can be repeated and the results averaged, to give a reasonably consistent result. So far, so good ....
In reality, it is an observed fact that the Australian Standard results obtained in this way, the same results that are on the windscreen sticker of every new car, are consistently optimistic compared to the fuel consumption actually obtained in the real world. I personally find that extremely annoying, and inexcusable. The 'Official" numbers are useful for comparing the fuel consumption of competing vehicles, but a complete load of rubbish for estimating what fuel consumption the average driver will actually obtain. The fact is, the standard test results are consistently optimistic, but WHY??? There are at least 3 reasons.
(1) Apparently in the interests of international standardization, Australia has chosen to use standard Euro Urban and Extra Urban test cycles, which unfortunately bear little resemblence to driving conditions in Australia. For example, Australia is sparsely populated, so our highway driving, on both major highways and country roads, consists of travelling large distances, at constant speeds of between 90 and 110 km/hr. You might therefore expect (or at least hope!) that the standard Australian Government fuel consumption testing would include a result that reflects this type of driving. Unfortunately not. The closest we get is the Extra Urban cycle, at an average speed of only 63 km/hr !!!!! Well, derr, how many of us in Australia travel at an average speed of 63km/hr on the highway!! Sure, if we travelled at 63km/hr on the highway, then we might conceivably obtain the rated Extra Urban consumption figures, well, so what. What bureaucratic idiot decided that international standardization was more important than producing a result that was actually useful? Yes, I find this sort of BS annoying. It would not be particularly difficult to define an Australin Highway Cycle, giving a result that, on average, actually reflects what highway consumption can be expected. Same deal with the city test cycle, which apparently simulates driving in peak hour in the middle of Paris, at a maximum of 50 km/hr, and an average speed of 19 km/hr. Even if you live in Sydney or Melbourne, I find it hard to believe that you clock up most of your city miles never exceeding 50 km/hr, and at an average of 19km/hr. What utter BS.
(2) Even if we adopted (or at least included) Australian Test Cycles, the errors in the Laboratory test measurements are significant. Despite what the standards people might admit, the main advantage of the Lab based Dyno measurement method is that the measurements can be done quickly and cheaply. Overall, this is still probably the only practical method, but it is certainly not free from errors. While the method avoids some errors associated with real-world driving, it adds many others. Firstly, the test cycles are obviously too short to provide a reasonable simulation of the real world. If you could eliminate all errors and spurious variable in real-world economy testing on the road, I'm sure no one would would even contemplate driving only 4km (as in the Urban cycle), and then claim that those 4km could reasonably represent city driving. Unfortunately, driving longer distances on a dyno is not practical. The next problem is that so many key variable, such as wind drag, have to be accounted for indirectly, resulting in significant errors that inherently don't occur in the first place with on-road testing. For example, I am very familiar with the 'coast down' method that is used for measuring wind drag at a given speed. It's actually not easy to do accurately, and this is one of many such cumulative errors inherent in the dyno approach. The experimentally determined wind drag, mass etc are then programmed into the dyno, which then adds further cumulative errors, for the dyno cannot simulate mass and drag with perfect precision, even if the variables are were known with perfect accuracy. Another potential issue, is that on the dyno, the vehicle is not actually moving through the air, even though the air drag is simulated at the drive rollers. Large fans are used to force air over the front of the vehicle to keep the engine cool, but it is not practical to provide an air blast over the entire front of the vehicle of 100km/hr, for example. This, in turn means that it is impossible to properly simulate the engine temperature under sustained highway conditions, and there could also be a difference due to a different 'ram effect' at the air intake. OK, so you get the idea. The dyno test approach simply swaps some of the errors of on-road testing for other errors, with the result that the published fuel consumption figures can only be taken as an approximate guide, even if we had proper Australian test cycles.
(3) Apart from irrelevant Euro test cycles, I would expect the published fuel consumption figures to be suspiciously optimistic anyway, because much of the key data required for the dyno testing is supplied by the manufacturers. The Australian Standards department simply does not have the resources to measure all the required variables for the dyno testing. For example, the manufacturer would normally provide the wind drag data, plus a lot of other data as well that gets fed into the dyno, or into the complex mathematical analysis that finally yields the fuel consumtion number. Now, I won't go as far to say that the manufacturers are blatantly dishonest (though some may be) but it seems inevitable to me that the data provided by the manufacturers will be as best-case and optimistic as it is possible to be without actually lying, and there is considerable scope for this given that much of the key data (eg wind drag) is experimentally derived. I'll also bite my bum if the vehicle used for the dyno testing is randomly taken from the production line - you can be sure they choose a 'good' one.
For all these reasons, the official Australian Green Guide fuel consumption figures are inaccurate, and invariably optimistic. With reasonable care, anyone can produce measured fuel consumption results that are both more relevant and more accurate that the 'official' figures.
puts it up to 8.2lph. I'm chuffed with that.
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