Fuel Efficient Driving

The two things that make the most difference for me are anticipating conditions so you don't use the brakes much and keeping top speeds low.
 
Uriel said:
The two things that make the most difference for me are anticipating conditions so you don't use the brakes much and keeping top speeds low.
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Indeed, fuel consumption gets kinda exponential once you go much over 60mph, and anticipation is a massive factor.

I have done some driving assessments for people wanting to drive more economically, and anticipation is the one thing that comes up every time.
 
I know about predicting conditions etc being good for fuel efficient driving.

What I am curious about is specifically the most fuel efficient way to get to speed assuming there is nothing that is going to cause you to brake and lose that speed again which would obviously be wasteful.

From looking at replies here and using google it now seems that fast acceleration possibly with gas pedal pushed almost all the way down is best for fuel efficient acceleration and then when you get to speed desired change to highest suitable gear to maintain that speed which is likely 5th but could be 4th if on a hill.

Also came across fuel consumption curves etc such as http://physics.stackexchange.com/questions/57888/why-does-higher-acceleration-minimize-a-cars-fuel-consumption but I'm not entirely sure I understand what it shows.
 
If only mythbusters tested quick acceleration then block change vs slow acceleration through the gears - they tested windows down vs aircon and changing lanes during heavy motorway traffic vs staying in the same lane.
 
Acme said:
I'll try the 1st 2nd 6th theory when I go home later... Will report back :p
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OK so I took the B roads to avoid traffic, and I encountered my 'commuter friend' in his Focus ST, so I ended up with 24MPG on the screen... :o :p
 
Outcast said:
WRONG. The distance you have travelled is far further by coasting than you would have achieved otherwise.

I am a "SafEd instructor" (Safe and Fuel Efficient Driving). All new trucks for example automatically switch into neutral to Eco cruise whenever the sensors detect declines.

They also do this just before you crest a hill and use kinetic energy to carry you over the top. This of course means our road speed plunges dramatically.
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I've noticed the 15 & 65 plate Scania & Volvos at work do this and tbh the speed drop off isn't too bad ~3mph I'd say, the fuel saving is significantly better, the sensors you refer to in Scanias at least is GPS cruise control, the truck knows when it's on a hill and acts accordingly as it reaches the summit.

I did Thurrock to Stoke last night in a thus equipped 65 plate Scania R450, fully loaded with washing powder and managed 10mpg, I know from doing that run more times than I care to remember in my old 12 plate that 8.5-9mpg was good going!

It's a bit disconcerting though when the thing drops to idle and displays N in the gear display when your coasting!

As far as efficient driving in a car goes then find out your peak torque rpm and always ensure you change up before you reach it, it makes quite a difference. :)
 
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RPM increases fuel consumption the most.

Using a lower gear and less throttle uphill uses more fuel than a higher gear and foot flat on the floor according to fuel consumption instant economy display, that and holding up traffic is why I mainly use hard accel and short shift, often skipping gears if sufficient torque.

You can test that yourself.

If you have an auto and it downshift's uphill, switch to instant economy, manually shift to higher gear and increase throttle and see which works for your car.

Manual, just try both methods.
 
Scania said:
I've noticed the 15 & 65 plate Scania & Volvos at work do this and tbh the speed drop off isn't too bad ~3mph I'd say, the fuel saving is significantly better, the sensors you refer to in Scanias at least is GPS cruise control, the truck knows when it's on a hill and acts accordingly as it reaches the summit.
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I wonder if this is contributing to one of the most annoying things I experience on the roads becoming far more common- the 3 mile truck vs truck overtake.

So what will now start happening is truck number 1 with his fancy GPS cruise detects that the crest of a hill is approaching and eases off, truck number 2 who is pinned to his limiter four inches off his back bumper goes out to overtake and when truck number one gets back up to speed is sat there like a lemon mid overtake... Fantastic.

I've given up worrying about driving economically despite my mileage going up considerably of late (1000 miles a week is no longer a rare occurrence) the pathetic 108BHP in my Passat basically means you have to use all the available torque to get it up to speed anyway. I tend to shift at or just before 3000RPM and use full throttle while doing so (obviously not around town :p ) and my average economy is the right side of 50 mpg.
 
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*yes this is getting a bit sad but...

Although it wouldn't show on an mpg counter, or even by calculating miles/fuel tank, I've often wondered how much I could affect my journey distance and therefore fuel required by taking a non erratic inside line and straightening the road approach

My journey to work is a 110 mile round trip with 104 of it dual carriageway, and a couple of times I tried to see how much i could effect the distance purely by influencing my pull out to overtakes and recoveries to lane 1, to line up with curves in the motorway to straighten the road and take the lesser distance inside lane (Can be either Left or right lane) It can be done in a way that would be oblivious to the rest of the road and isn't dangerous, however I haven't yet managed to maintain my concentration long enough yet to complete more than about 20 miles attempting this :-)

You might think its negligible but there is a 10% greater distance between lane 1 and 8 on an athletics track, so thats an extra mile every 10 miles!!
 
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lordrobs said:
I wonder if this is contributing to one of the most annoying things I experience on the roads becoming far more common- the 3 mile truck vs truck overtake.

So what will now start happening is truck number 1 with his fancy GPS cruise detects that the crest of a hill is approaching and eases off, truck number 2 who is pinned to his limiter four inches off his back bumper goes out to overtake and when truck number one gets back up to speed is sat there like a lemon mid overtake... Fantastic.
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Pretty much, yes unfortunately. Although a lot of it is down to inconsiderate driving on the part of the truck being overtaken, it's not hard to lift off to let him pass in full knowledge he can subsequently pass later...

Most don't and are set in the "your not getting past" mindset, pretty daft really, the vast majority of drivers are paid by the hour....

Incidentally, if you keep your foot planted on hills, Scania's won't back off even if the cruise is on, it'll instead hold its speed, subject to load weight, incline and engine power....
 
GPS coast is more of a problem when you've just overtaken another truck, pulled into lane 1 and not realised it has dropped into "eco".

Also ... Wait until that new Scania misreads that truck parked in a layby and slams its brakes full on !

We've had to send ours back to be recalibrated. Now they beep for about 3 seconds before slamming the brakes full on !!
 
joeyjojo said:
The figure in the above seems to disagree.
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Going by my experience not his, if you rev an engine more the injectors are firing more often. When accelerating you need more fuel anyway, so combine that with higher rpm and longer duration in lower gear you use more fuel. I negate this by missing gears on the way up. If you accelerate gently you will go through all gears to achieve the same but drive everyone behind you nuts.

That graph shows gallons per KWH, ie per BHP, once you go higher in rpm your BHP increases so that flattens the line. Using miles would change that graph completely as we use gears to improve the efficiency of the engine.
 
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Dr Who said:
Going by my experience not his, if you rev an engine more the injectors are firing more often. When accelerating you need more fuel anyway, so combine that with higher rpm and longer duration in lower gear you use more fuel. I negate this by missing gears on the way up. If you accelerate gently you will go through all gears to achieve the same but drive everyone behind you nuts.

That graph shows gallons per KWH, ie per BHP, once you go higher in rpm your BHP increases so that flattens the line. Using miles would change that graph completely as we use gears to improve the efficiency of the engine.
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I might try this with a datalog on the hill outside my house tomorrow comparing injector duty cycle between 3rd, 4th and 5th
 
Outcast said:
GPS coast is more of a problem when you've just overtaken another truck, pulled into lane 1 and not realised it has dropped into "eco".

Also ... Wait until that new Scania misreads that truck parked in a layby and slams its brakes full on !

We've had to send ours back to be recalibrated. Now they beep for about 3 seconds before slamming the brakes full on !!
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Not had that auto braking experience (yet) with a Scania, I've experienced it in a new Volvo FH when a transit driver decided to brake check me for whatever reason, it pulled me up remarkably well and when I got to my delivery I expected my 26pallets of bottles to be shot forward, not one had moved!

With the Scania's I just experience the lane change warning, often when your nowhere near the white lines which is a bit annoying....

For those unsure what we're on about....

Scania lane change warning system...

Emergency braking system on a Volvo FH.

 
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Dr Who said:
Using a lower gear and less throttle uphill uses more fuel than a higher gear and foot flat on the floor according to fuel consumption instant economy display, that and holding up traffic is why I mainly use hard accel and short shift, often skipping gears if sufficient torque.
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Do you have a diesel or petrol? My wild guess would be that the most fuel efficient way to get up a hill would be with the revs near peak torque for your engine - which for diesel would usually be lower down in the rev range than a petrol.

I don't get instantaneous consumption displayed in my car so can't go test what's best for me unfortunately. I usually go for a gear that will require the accelerator to be around 50% depressed.
 
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