How is l/100km calculated?

I agree with the comments on how the cars computer calculates it. My current Opel Astra (piece of shyte) does not count any consumption when the car is stationary (at a stop). Which is soooo very wrong, because the engine is using fuel as it is running, and no distance has been traveled, essentially this is when a car is at its most uneconomic (0 km for X petrol). So I dont pay it any attention, Just do the calc yourself by km done and petrol used. Do this 3 or four times and you will get better results.
 
ya its not always completely accurate !

but that far out ! thats horrible, i have an alfa, and at worst its .2L/100 out.
 
alkit said:
Thanks guys for all the responses.

I apologise, but I don't think I phrased my question correctly, it should be like this:

My car claims a combined average of 7.7l/100km. According to my onboard computer, I have averaged (since last tank full) at 8.2l/100km. That seems 100% ok.

What I don't understand is why my tank is showing empty at 320km. I should be able to get over 500km on a 45l tank...

That means I am technically using around 14l/100km, so to me it seems like the engine is gulping petrol and the onboard computer is very very inacurate.

So my q is - why am I not getting over 500km off a tank like both the specs and computer of my car are reporting?
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Because you're not using your whole load of petrol? :confused:

Is that hard to notice? When you fill up, you probably only put in 38-42 litres. if you drove the tank dry you'd get your 500km.
 
Fazda said:
People are also very quick to read road tests where fuel figures are given and expect to come out on those figures. The chance of your car producing the same figures as a test car is highly unlikely. In some cases you will do better, and in others, much worse.

A road test figure simply gives you a ballpark idea but can never be stuck to in every day driving. If you take the daily trip into work, all you need is one accident or one traffic light on the blink and your figures can go to hell.
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BUT, if these tests are relatively similar, you can get a ballpark efficiency indicator for the car being reviewed. Sure, your driving style/route will be different so consumption will differ. If you know that one car is noticeably less efficient (from road test figure) you might pick a different one if your're looking to buy...

The 'combined cycle' or something that is used should probably be standardised. ISO something or other- a repeatable on a closed course test that all cars can do so an accurate measure of their efficiency relative to each other can be given.
 
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