Driving economically?

Given the silly fuel prices I was wondering which driving style will give better MPG and save fuel?

For e.g: If I'm driving at a steady 40mph along a flat road using about

1/4 throttle in top gear and I approach an incline, to maintain a steady 40mph will it be better on fuel if I change down a gear and use higher RPM but less throttle? or is it better on fuel if I remain in a high gear but use more throttle and less RPM?
Reply to
John
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It would depend on whether the engine would be labouring or not. If you were driving a non turbo diesel (eg. an old BX frinstance) then you could get away with it but in a petrol or turbo diesel probably not. If you treat the accelerator like it's made of glass then you won't go far wrong. Plus keep the car moving, anticipate where you might need to stop etc., because it's the changes of speed that use up the fuel more than a constant speed.

Reply to
Malc

Also, consider that every time you brake you are effectively using fuel, in that you used fuel to get to that speed and now you are throwing that speed away. Don't read into this that I don't think you should brake, just that by driving in a certain way (not too close behind another vehicle, for example) you may reduce the amount of times you have to brake.

Rob Graham

Reply to
Rob graham

Did you miss the fuel saving device?

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Reply to
jOn

As an aside, I read the other day that, as a rule of thumb, you burn an extra litre of fuel for every 20 miles travelled at 80mph instead of 70mph.

Does that sound true?

Reply to
David Quinton

I suspect that's a bunch of crap. That would equate to something in excess of a 25% reduction in fuel economy on a car that does 40mpg at

70mph. IME driving, e.g. 2 litre family saloons, the drop is something more like 10%. However, you do get a massive decline in mpg when you go much over 90mph, where the wind drag is really punishing you.

Jim.

Reply to
Jim Walsh

Use the highest gear that allows the speed to be maintained.

Reply to
Dave Plowman (News)

It of course depends on the drag of the vehicle and what its fuel consumption is at 70 anyway. When giving a guestimate like this a percentage figure *might* be better, but not the same attention grabbing headline as 'save a quid every 25 miles' or whatever.

Reply to
Dave Plowman (News)

Yes, something like that.

Ages ago there was a government TV advertising to discourage so called lead footed drivers. The intention of the ad was to save the nation's fuel, but the ad was discredited by professional engineers. It was a knee-jerk, hare brained reaction. Driving in a higher gear may require a deeper throttle position than a lower gear, but is nevertheless more fuel efficient.

Reply to
Johannes

Yes, this has to be tested. My calculation shows that 1 litre over 20miles corresponds to a drop from 35mpg to 25mpg, this seems unrealistic.

However, many cars these days are geared at 20mhp/1000rpm for good acceleration, but this is not really high enough gearing for cruising effortlessly at 80mph. At 4000rpm there will inevitably be noise and wear. My car is geared at 24mph/1000rpm; that gives 2917rpm at 70mph, which is much more restful.

Reply to
Johannes

What saves more fuel is how you approach traffic lights, roundabouts and junctions.

The idea is to approach them and time it so you never actually stop rolling. It does mean however that you need to back off a bit further back so YOU are controlling when you set off, not the vehicle in front.

Reply to
Conor

Conor ( snipped-for-privacy@gmail.com) gurgled happily, sounding much like they were saying :

"The right pedal uses fuel, the middle one wastes it."

Reply to
Adrian
[...]

On a recent European trip I was getting ~24mpg while averaging ~75mph (60-90 mostly, not much WOT) which dropped to ~18mpg while averaging ~130mph (90-160 mostly, loads of WOT). I suspect most of the difference was fuel used regaining fast cruise after being slowed by traffic rather than maintaining the higher speed.

I doubt if there is much fuel penalty for me doing 80 rather than 70.

:)

A
Reply to
Alistair J Murray

Not on my BMW 528 auto either. Setting the cruise control at 75 gives 34 mpg on a reasonably clear motorway over long distances. Nudge it up to 90, and it drops to 32.

Reply to
Dave Plowman (News)

Thanks for sharing that with us, git! :)

Reply to
DervMan

I find that driving below 200mph saves some fuel.

Reply to
Johannes

It might - depending on the vehicle and gradient. The below won't apply to your car unless it's an Endura-E Ka, but the idea may well be similar.

I've done quite a bit of work into this with our own Ka. I've plotted relative engine efficiency, as dictated by the throttle and calculated load readings, across lots and lots of engine speed. Trying to compare gear for gear is meaningless, but the engine appears to be at its most relaxed compared to what it is capable of porducing when cruising between just under

2,000 rpm to around 2,850 rpm.

The Ecotek valve influenced the chart, almost certainly because it was leaking air into the system, which was changing the calculated load figure. I'm pleased to report that there was no difference in fuel consumption after removing the device so the valve doesn't break the laws of physics as some of my fellow Ka peers claim. :)

Check out the graph (nice orangy background, heh, sorry) here:

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\dervman\donkeffic.jpg At 40 indicated in top, our engine is turning over at around 1,850 rpm and at 2,330 rpm in fourth. At 40 GPS-corrected, we have around 2,000 in fourth and 2,500 rpm in second. If I stick to an indicated 40 I should probably use fourth... and certainly when I come to a hill. If my chart has produced meaningful data...

That's the $64,000 question though!

Reply to
DervMan

"DervMan" wrote in news:x4EQe.7150$ snipped-for-privacy@newsfe7-win.ntli.net:

At 40 GPS-corrected, we have around 2,000

^^^^^^^^^^^^^^^^^^^^^^^^

Blimey - that's high gearing for a Ka! With a redline of, say, 6000 rpm, that gives you a max speed of 96mph in second! ;-)

Reply to
Stu

Stu ( snipped-for-privacy@home.com) gurgled happily, sounding much like they were saying :

Not to mention that third is rather pointless with second and fourth only

500rpm apart.
Reply to
Adrian

You've never driven a Ka then? You don't know that it has 600 bhp?

I don't know why I wrote "second" when I meant "fifth" hehehehe. :)

Reply to
DervMan

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