Why we never seem to match manufacturers quoted MPG

[Welly]

Ever wondered why it's so hard to get near the quoted MPG for your car?

This univeral test might help to explain why......

FUEL CONSUMPTION TEST (Directive 80/1268/EEC as amended by 2004/3/EC)

The new test has been agreed internationally and provides results that are more representative of actual average on-road fuel consumption than previous tests. There are two parts: an urban and an extra-urban cycle. The test cycle is the same as that used to determine the official exhaust emission classification for the model of vehicle in question.

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 20°C to 30°C 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 31 mph (50 km/h), average speed 12 mph (19 km/h) and the distance covered is 2.5 miles (4 km).

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 75 mph (120 km/h), average speed is 39 mph (63 km/h) and the distance covered is 4.3 miles (7 km).

Combined Fuel Consumption Figure
The combined figure presented is for the urban and the extra-urban cycle together. It is therefore an average of the two parts of the test, weighted by the distances covered in each part.

[Doggy]

I'm trying to decide whether that's a level virtual playing field, or a virtually level playing field

Either way, at least it's the same every time. What relation it bears to reality though, I'm not sure.........

[Welly]

What relation it bears to reality though, I'm not sure.........

Well if it is carried out in a nice cosy Laboratory then where's all the wind resistance we get out on the roads? (unless they actually blow air at the car?)

You can see the idea though I suppose, comparing like for like, like

[mjb]

I just wonder how they get around the fact that they're accelerating on a rolling road, where the vehicle's weight has no effect on the effort required to accelerate (hint, you can accelerate from 0-150mph in about a second and use virtually no fuel to do it if you're on axle stands...), unless the rolling road is setup to increase+decrease resistance to mimic it...

Still, I find I can greatly exceed the manufacturer's quoted economy figures if I want to ;)

[nutski]

I get told by my other half its because i have a heavy right foot....