ok so here one:

would a car being driven a lower gear with the accelerator pedal slightly pressed (higher revs due to the gearing) be more economical than if it were driven in a higher gear, with the accelerator depressed almost fully (but with lower revs)??

so is it revs that you want to keep away from or do you want to keep the accelerator as far from the floor as possible?

Both!
Too many revs and the engine is spinning faster using more fuel, too high a gear and the engine isn't running fast enough to pull and dumps more fuel in to get it going.
Try and keep the revs between 1,500rpm and 3,500rpm and accelerate smoothly rather than stamping on the gas or being in 5th at 40mph.

find the torque curve for your car and keep the revs in the highest range

Thrash the spuds off it and have fun before the oil runs out!

More seriously though, it's not that clear cut…. Smoothness is key. No use accelerating in any gear if you can see traffic stopped 200 yards down the road, just roll up smoothly, off the gas. You'll still be stopped in the same place
Instead of flying up to red lights and braking, roll off the power very early and try to keep it moving for longer so they change to green: Stop/Start is your worst enemy!
Try and accelerate when going downhill (Or back right off to keep the same speed) and let your speed drop slightly going uphill if possible
That sort of stuff…
Looking FAR ahead is everything 🙂

turn your front fog lights on, they help

the cooler you look the better your mpgs will be

hmmm anyone got the torque curve for a volvo 850 GLT, I'd guess its practically flat! 😀

oh and only have rear fog lights, jeeze! last night, driving in the pissing rain and every dog and his man had their bloody front xenon fog lights on which had the effect of reducing my visibility down to about 2m as they howled past :grr:

a volvo?

in that case drill enough holes in it to bring the weight down slightly below a challenger tank and you'll be fine

😉

hmmm anyone got the torque curve for a volvo 850 GLT, I'd guess its practically flat!

If it's petrol then it probably is flat.

Anyway, generally higher gear = more economy.
The faster the engine turns the more energy is wasted in friction.

Remember that the pedal controls (roughly in most modern cars as they are electronic, especially if it's a diesel) the amount of fuel per revolution, not the amount per second, so lower revs with the pedal in the same position uses less fuel (and gives you less power of course).

For the same power, a higher gear with more pedal will still give better economy unless it's not burning the fuel efficiently (too much per cycle perhaps?)

Yup, it's way harder to explain than that – there are far too many variables to state anything other than the ideal case.

Use the highest gear you can as long as the engine is not labouring (ie any anti stall devices are not firing in fuel you haven't requested). In a diesel car, you should be able to up through the gears without any use of the throttle at all, this will give you an idea of the lowest speeds you can run in in any gear. The anti stall will fuel you until the engine is happy to run at that mix (zero throttle) and that is the lowest speed you should use in that gear. Shift up early (if your lowest speed in 4th is 30mph, shift up into 4th at 33 ish), and use as little throttle as possible, anticipate slowing down and try to keep rolling (using the brakes and low gears are your enemy, so stop start driving is evil!)

High gear + light throttle = low fuel consumption.

If you have an instant fuel cosumption readout, drive at a constant speed (say 30mph) and choose 2nd 3rd 4th etc until your engine labours, and see what effect it has on your economy. You'll neeed to use more throttle in second than in the higher gears, so economy falls. In 4th, you should be using light throttle and a longer gear, so economy is good. In 5th, you might start labouring, so you might not be as efficient as 4th, but if your engine isn't labouring, then the higher gear is always more economical.

MMW you are dangerously close to the truth, my 850 weighs about two ton!!!

(but then it is wonderful in all its grunting wardrobish monsterousness)

My Passat Est weighs 1600kilos – not exactly lightweight.

Smooth driving has two economies, one is fuel consumption, the other is that the car will last longer and you'll get through fewer consumables.

I used to drive vans with several million pounds worth of delicate artwork in the back, the odd national treasure amongst them. You learn to drive smooth! If we were ever to have had one mishap the company's reputation would have been in the gutter and our insurance premiums would have been so high we'd never be able to work again.

I drive like a chauffeur now. (But not like Henri Paul)

As above, slightly higher revs with light pressure on the throttle is far better than straining the engine in too lower gear with the throttle wide open chucking fuel in. Genrally speaking, as lower revs as pos without labouring. But the rule isnt bullet prof. for example, my 2.2 petrol gets better economy in 4th at 60 than in 5th even though the engine dosent struggle at all in 5th at that speed. Its all down to the torque curve of the engine as mentioned above. The rev range that returns the greater torque is where the engine is most efficient. Stay in this band perticually when accelerating and you should save more fuel.

MTFU and sell the coffin, ride your bike. Now that's good fuel economy.

my V6 Golf gives best economy when driven in 6th round town. I can just get high teens. Use 1/2/3rd as per textbook driving and its 11-14mpg.

BMW drivers long ago sussed out that indicators use a lot of fuel.