Blow me if I can get my head around the maths on this one.
If I wanted to maximise economy over (say) one minute is it better to
1) Put my foot down and go from 0 to 60mph in (arbitrarily) 10 seconds, then spend 50 seconds cruising at 60mph.
2) Ease onto the throttle as if it were nitro-glycerine and take 30 seconds to get to 60mph, then cruise at 60mph for the remaining 30 seconds.
Which technique will use more fuel?
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I think one of the Breakdown companies (RAC?) did some research into this and came to the conclusion that option 2 in your list uses more fuel.
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I could well be wrong but ...
I'll stick my neck out and say option (1). My O-level physics from 1981 tells me that, in a loss free system, the two cases require exactly the same amount of energy/fuel.
However, if you run the two scenarios side by side, at the end of 60 seconds the first case is 300 yards further down the road than the second. That's got to use more fuel.
A lot depends how the acceleration is achieved. Accelerating in too low or high a gear does nothing for engine efficiency.
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"Loss free" would have to include no unburnt petrol being lost out from the system.
A foot flat on the floor would surely result in unburnt fuel being lost, whereas the gradual approach would not, or at least not to the same xtent.
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Look here:
www.potn.co.uk/potn/print.php?sid=66
Most people could probably gain at least as much by leaving a longer gap behind the car in front thus allowing grater anticipation and gentler decelleration IMHO.
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Most drivers - when faced with a straight road between 2 slow bends, will accelerate gently for about three-quarters of the straight THEN brake for the next bend.
I advocate using as much power as you are happy with (yes, up to FULL) for the first, say, third - when the view is best at the beginning of the straight.
During this time, assess the speed for the oncoming bend and gradually ease off the power, so that engine braking brings the speed to exactly that required.
Fuel consumption is the same for bothe methods, if speed and distance are equal, BUT acceleration sense assists concentration, alertness and safety.
Acceleration uses fuel - but brakes waste it.
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The winners of all the Economy Runs I have heard of, have won by keeping the throttle as closed as possible (and using brakes as little as possible, which turns forward motion into friction and heat). You don't have as much fun, but there's more cash left in your wallet.
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www.telegraph.co.uk/news/main.jhtml?xml=%2Fnews%2F...l
The relevant passage is:
"Mark Dougherty of the School of Transportation and Society at Borlange, Sweden, which supervised the project, said: "They think to accelerate gently will get a better fuel consumption. That's basically wrong." The key to fuel-efficient driving is to accelerate hard without over-revving the engine and to move through the gears briskly so that the car reaches its cruising speed quickly."
I've always hoped this was true...
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I have memories of the venerable LJK Setright writing something similar in Car magazine umpteen years ago. He was to take part in an economy run and made the point that a carb. engine would run most efficiently at full throttle.
Darcy.
People who live in Glasshouses have an HG3 postcode.
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Just a few thoughts:
Theory might suggest that a car would use twice as much petrol at 4000rpm than at 2000rpm. (Assuming that the engine always injects the same amount of fuel at all engine speeds.) Is this likely to be true in practice? I suspect not, as in order to increase the engine speed, more fuel needs to be added, though this reduces once the engine has reached that speed.
Having been trying out various driving styles between petrol fills, and calculating the mpg, I get the impression that accelerating reasonably rapidly to get into the highest gear as soon as possible is beneficial to economy - perhaps 10% better. I normally keep below 2500rpm both when accelerating and when at a constant speed.
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