It is normally close to your torque peak, since your engine is working at it's most efficient at that point. Or at least that is how I have always understood it. I am sure I have some old car magazines lying around, will see if I can find specifics.
like driving like an angel for most of the tank, thinking you have achieved such a good consumption for the tank, and then being caught in some horrendous traffic jam, which blows your consumption figures straight to you know where.
yeah, lol! I did a lab in university on a ford 1.6 petrol against a water brake to plot out the engine characteristics. just thinking that if i cruise around in 5th at 30mph, then my engine might not be bruning fuel efficiently at those revs. But then would there still be minimal fuel used as no need for peak torque?