optimum fuel economy
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55.3mph
Soldato
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What is this fuel economy of which you speak? Is that when you don't see your fuel guage physically creep downwards because of just how hard you're hooning it?
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on my private dual carriageway m'lud
*on my private dual carriageway m'lud
Jez said:
Unless it's say 55mp in a 20
But as Jez has said, it really does depend upon what car you're driving, its engine efficiency, gearing, power, weight, etc etc, but I've heard 55 as a general ballpark figure, but it's probably +/- 10 mph.
DaveyD said:Unless it's say 55mp in a 20
But as Jez has said, it really does depend upon what car you're driving, its engine efficiency, gearing, power, weight, etc etc, but I've heard 55 as a general ballpark figure, but it's probably +/- 10 mph.
what does weight have to do with fuel efficiency at a constant speed?
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Clarkey said:
Less weight = better fuel economy
BeatMaster
Clarkey said:
I suppose for example if you had 2 cars with the same size tyres. The heavier one would have a larger contact patch with the road due to the tyre being misshapen more. Also on average heavier cars do have larger tyres, so this will increase the friction against the wheels turning.
Clarkey said:
Requires more power to keep speed constant when going uphill?
I get better figures on the trip computer doing 85 than 75. Over 90 and it starts drinking presumably because of the short arse aerodynamics.
Clarkey said:
Surely you'll use less fuel driving on your own in a car compared to driving with 3 large blokes + boot full of luggage giving say an extra 200kg of weight in the car.
Edit, though you're probably right when up to a constant speed, but you've got to get to that speed in the first place
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Weight obviously makes a huge difference to fuel economy when accelerating or going up hills - and you do get them on motorways of course.
It also makes a difference to the magnitude of frictional resistance when maintianing speed, but how much? And how much if at all with the component of wind resistance?
So you wouldnt expect weight to be that much of a factor on long stretches of empty motorway.
It also makes a difference to the magnitude of frictional resistance when maintianing speed, but how much? And how much if at all with the component of wind resistance?
So you wouldnt expect weight to be that much of a factor on long stretches of empty motorway.
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frosty03 said:
Surely it must be the lowest rpm for a given speed. Though without knowing engine mapping characteristics ( to know how much fuel is injected for a given engine condition) it would be quite tricky to guess it.
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That would be true but for air resistance which rises exponentially above 60 whereas rolling resistance is a constant, hence the midway cutoff point of 55mph or so.
50 would be a good speed but its a bit dangerous so 60 is my advice, only 10mph slower then the limit but on long journeys it would make a few quids difference.
Weight doesnt really matter too much at a constant speed, even a big heavy car can do good mpg on a motorway but around town its much more unlikely because its a far greater factor in accleration then a top or constant speed
50 would be a good speed but its a bit dangerous so 60 is my advice, only 10mph slower then the limit but on long journeys it would make a few quids difference.
Weight doesnt really matter too much at a constant speed, even a big heavy car can do good mpg on a motorway but around town its much more unlikely because its a far greater factor in accleration then a top or constant speed
aztechnology said:
You don't exactly get a choice of what RPM you are doing if you have a manual box!
But certainly higher engine speed = more frictional losses, lower engine speed (to produce the same power) = higher volumetric efficiency and better thermal efficiency due to increased compression ratio.
I did try a few experiments when I had my XJS (5.3 V12). I had the center exhaust boxes removed as this improves fuel economy substantially at the expense of a bit more noise.
I found that on the flat, 55-57 was optimum giving ~28 MPG. However, on my test route (M25 from J13 to J8) I found that this constant speed only gave ~24MPG due to the hills. If I held the pedal in a constant position so that I would be doing 56 on the flat and allowed the car to speed up downhill and slow uphill, I could get ~26MPG.
Obviously, I didn't buy this car to sit doing 55 on the motorway, so I rarely saw more than 20MPG.
I found that on the flat, 55-57 was optimum giving ~28 MPG. However, on my test route (M25 from J13 to J8) I found that this constant speed only gave ~24MPG due to the hills. If I held the pedal in a constant position so that I would be doing 56 on the flat and allowed the car to speed up downhill and slow uphill, I could get ~26MPG.
Obviously, I didn't buy this car to sit doing 55 on the motorway, so I rarely saw more than 20MPG.