How to drive down the cost of driving your car

[culzean]

if I understand correctly, hard acceleration in itself is more fuel efficient than mild acceleration
http://en.wikipedia.org/wiki/File:Brake_specific_fuel_consumption.svg

so if one joins free flowing A road and needs to get up to speed there is no fuel saving in mild acceleration
one could argue that there is, by staying in sub-50mph for longer

anyone who has ever experimented with fuel saving driving knows that accelerating slowly and trying not to brake or ever come to a standstill gives you the best results.  If you accelerate hard and get to 60 in say 100 yards, you now have to fight 60mph drag and rolling resistance for 1660 yards before you have covered a mile,
your average speed for the mile would be pretty much 60mph.

if you accelerate in a linear fashion for the whole mile the wind drag and rolling resistance will only be at 60mph level for a short distance, your average speed for the mile will be 30mph, it will take you longer to cover the mile.  However there is no time involved in MPG,  it is simply miles per gallon, so it may take you longer but you will cover the mile using less fuel, which is the whole object of the exercise.

 I don't think anyone can argue that by accelerating harder, driving faster and braking harder that you can ever use less fuel than by driving more smoothly and planning ahead.

[dg]

you're using exactly that argument of wind resistance here which is separate topic

I am just making it clear that accelerating hard when you need too actually is fuel efficient

wind resistance is separate valid concern applicable at 45-50mph+
so one could accelerate hard up to 50 and then potter along at the same speed and not braking 

[culzean]

air resistance is definitely involved in fuel usage because if you ran the car in a vacuum at any speed you would get fantastic mpg. Air resistance is there at any speed, are you saying that the air only suddenly appears around the car at 45mph ?

it is a given that to accelerate a given mass in a shorter time will take more power than if you take a longer time - and power in this case is the rate of using fuel, which is what you are trying to save.

[dg]

45-50 appears not suddenly, I can not look it up right now, but for ICE cars, under 30mph drivetrain and other inefficiencies are responible for most of loses
wind resistance grows non linearly, so from top of my head it becomes dominant/significant at threshold I mentioned.

for BEVs on the other hand other losses at low speeds are much less noticeable, so there is more noticeable gain from driving at lower speeds.

[dg]

but you will spend more time to cover same distance at lower speed, thus more time burning fuel, so it's not as simple as you're trying to put it.
I'm not in wind resistance denial though

it is a given that to accelerate a given mass in a shorter time will take more power than if you take a longer time - and power in this case is the rate of using fuel, which is what you are trying to save.

the only credible test for particular car would be to have scangauge attached driving in different styles for a while, but it might be a bit difficult in practice to change habits or make it comparable because of weather, traffic, etc

[culzean]

but you will spend more time to cover same distance at lower speed, thus more time burning fuel, so it's not as simple as you're trying to put it.
I'm not in wind resistance denial though

there is absolutely no time factor involved in miles per gallon, it is simply the 'amount of fuel used to cover a distance',  it does not matter if you take all day driving at 10 mph.

power however does have a time involved as it is energy x time (a joule is a watt per second,  a KWh is a 1000watts for an hour.  the faster you accelerate or the faster you travel the more power you need to use.  As the energy is supplied solely by the fuel you are using,  it means you burn more of it.

[dg]

I'm not really sure what are you trying to prove.
yes the higher the speed - more energy needed to sustain it due to wind resistance, no argument here, I already answered that, even in first post.
People could not travel at 30 mph on motorway or A road.

Acceleration has nothing to do with speed you are accelerating to.
I'm not urging you to drive faster.

Just pointing out that accelerating faster to the desired speed sometimes means:
that you will be getting more energy extracted from the same amount of fuel burned
than by accelerating slower.

[bill ericay]

As Harry Hill would say, there's only one way to settle this................fight!

[culzean]

I'm proper bored now -    next topic please

http://www.autoexpress.co.uk/car-news/31861/mpg-mythbusters?utm_source=taboola-interna