I thought that the fuel consumption is related to the revs and not the gear that you are in. Is this not the case?
If you are doing say 2,500 rpm in 2nd gear then you are covering alot less distance than doing 2,500 rpm in 5th gear.
The Rpm refers to how many revolutions the engine is doing, not the wheels. Therefore, the engine will operate less times to travel a certain distance in 5th gear than in 2nd. And therefore use less fuel.
However this of course needs to be offset by the fact that when you start going abouve 60 mph then wind resistance becomes an increasing force and will therefore need more effort (fuel) to maintain that speed.
In short, if you are in a low gear, say 2nd, the engine does not need much effort to maintain speed, but operates lots of times to cover a short distance.
Higher gear needs more effort but operates less times:
imagine you are on riding a bike.. peddling like mad in a low gear is wastful, too high a gear and you need legs like tree trunks.. There is an optimum speed thats comfortable and efficient).
If the revs are too low, then the engine labours, is not operating in an efficient manner. So its not a case of getting the revs down to next to nothing, this isnt efficient and isnt good for the engine either. High revs causes wear, but so does not enough revs.
When on a level road 1,800- 2,000 rpm seems sensible (to maintain a speed), however if you come to an incline then more revs would be appropriate to avoid the engine labouring.
You can get away with slightly less revs in
lower gears than higher gears as less effort is required to maintain speed.
hope that makes sense!?