Petrol prices, and driveing sloooooow

Hi dudes.

I have noticed with the increase of fuel prices that ppl are driveing slower.

Does driveing slower actually save you money.

I figure. ( but I am a dill )

Weight of vehicle X distance travelled X rpm X time = fuel used.

So if you go slower it takes longer to use the same fuel for the journey.
But your fuel cost for the journey is the same.

If you travel faster ( Im talking of 100 kms ) you get there useing the same ammount of fuel as someone traveing at 70 kms, but faster.

I know there would be wind resistences etc.

But all these ppl travelling at 70 kms, are they saveing fuel??

Al :confused:

Yes.
Air resistance is a square law.
Double the speed, four times the energy required to overcome the air.
Dropping the speed does improve fuel economy.
Try riding a motor bike to check out the air resistance.

I cant claim any real knowledge just some research and personal experience, having lived around cars fanatics all my life. You wont save much fuel by travelling slower in most cars, the only time being slower really can save you fuel is in the take off. The only real way to save fuel is to keep a constant speed at all times. Let the car do the slowing for you. On take off gently, gently until you are up to speed. so these 5 changes of speed limit in 5 K's really screws with that.

Thats my 2c anyway.

You are probably thinking right Al

Each car will have a 'most efficient' speed.
What that is depends on the engine design, gearing, body aerodynamics etc.
The speed is probably somewhere between 70 and 110 ks, but to work it out you need a trip computer. 2 cars I've driven that had one were an Audi 100, and that showed least fuel used at 110 kph :eek: The other was an old 1300cc Mitsi mirage, and even that got best economy at ~100kph. (and 70kph was about the same as 115kph)

So I guess they say your mileage may vary :confused:

Cheers

Ian

With highway driving I've found I get around 150kms per litre if I drive at 90kph instead of 100kph or more.

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Originally Posted by MathewA

With highway driving I've found I get around 150kms per litre if I drive at 90kph instead of 100kph or more.

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Thats some lean vehicle you drive Matt.
I get 16l per 100 kms out of mine.

Al :)

I think I need to re-write that. I get an extra 150km per fill up if I keep the speed at around 90kph than if I drive at 100kph. About 750km/42litres

MPG is far easier to work out isnt it?

Took me ages to figure out this metric rubbish.

Al :)

Accelerating quickly also uses more petrol. How fast can you get to 60kph?

I know accelerating quickly uses more fuel, I assume all you old buggers drive smoothly and calmly.

No harse accelerating, braking. etc.

Al :rolleyes:

Maybe, the day will come where petrol will become so expensive we'll be cutting holes under the pedals and just run our cars to and from work ,,, Fred Flinstone style.

Be good for the environment, wouldn't it ?

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Originally Posted by apricotripper

Maybe, the day will come where petrol will become so expensive we'll be cutting holes under the pedals and just run our cars to and from work ,,, Fred Flinstone style.

Be good for the environment, wouldn't it ?

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Yabba dabbaa doooo!!!!!

Fred :p

Just be happy that ya car doesn't run on ottled water or Coke. :rolleyes:

High petrol prices have increased the cost of lots of things delivered by road, Bread, milk, vegies, meat....I'm wondering if the price of petrol also increases the price of petrol. It's delivered by road too ? :rolleyes:

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High petrol prices have increased the cost of lots of things delivered by road, Bread, milk, vegies, meat....I'm wondering if the price of petrol also increases the price of petrol. It's delivered by road too ?

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Quite so, Gumby. It's a vicious cycle. The price of petrol increases the cost of delivering petrol which in turn increases the price of petrol which in turn …

Expect the price to be $10 per litre next week

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Originally Posted by Cliff Rogers

Just be happy that ya car doesn't run on ottled water or Coke. :rolleyes:

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Cliff...youve hit the button!!

People who complain about paying $1.30 a litre for petrol don't bat an eyelid at paying much the same price for bottled water.

They tend not to buy 60 bottles a week thought.

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Originally Posted by Gumby

High petrol prices have increased the cost of lots of things delivered by road, Bread, milk, vegies, meat....I'm wondering if the price of petrol also increases the price of petrol. It's delivered by road too ? :rolleyes:

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Most petrol tankers are diesel powered
:)

Thats why you need to drive a v8 landcruiser

Uses a &^%&* load whatever speed you go;)

And the quicker we use up all the fossil fuel the faster earth can recover;) .

Looks like I'm a greenie after all. Now to save some trees!

dazzler

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Originally Posted by Grunt

They tend not to buy 60 bottles a week thought.

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People in this great country need to realise that the water is going to run out before the petrol does.

Well, we did a trip recently, about 500km return. Normally the car gets about 450-500km to a tank, but including that trip, nearly 600km.

The scary part is we were doing about 130 in both directions... :D

In cars with half decent fuel injection systems, it also makes sense to keep the revs low. If the brainbox decides you are wanting more go, it will dump bulk fuel into the engine, especially on those cars that have a bit more go than standard. I know with the RX-8, it's about 4,000rpm, and the fuel economy goes out the window.


Next car will be a hybrid for us thanks. ;)

I'm getting about 5.4l per 100km out of my Hyundai Accent, having changed 3 things:

1) removed the convoluted resonator before the airfilter box, and replaced it with a straight tube from grille to filter box.
2) stick it in neutral any time the road slopes down.
3) given up washing the car. I used to believe that the air resistance bit was lowered if the car was smooth and slickly polished, but look at shark skin, whale skin, golf balls, olympic swimming costumes. They all have lumps and bumps to deliberately create a small layer of turbulence close to the surface, which is supposed to reduce resistance all over.

Cheers,
Andrew

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3) given up washing the car. I used to believe that the air resistance bit was lowered if the car was smooth and slickly polished, but look at shark skin, whale skin, golf balls, olympic swimming costumes. They all have lumps and bumps to deliberately create a small layer of turbulence close to the surface, which is supposed to reduce resistance all over.

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Thank you, now I finally have an excuse.

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Originally Posted by Grunt

Thank you, now I finally have an excuse.

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Don't forget, you save even more fuel if the boot is full of fishing gear and the cabin full of sand ... like mine :D

Richard

I found what buggers my fuel economy on my Cruiser is SWMBO towing the float with two TB's and the hand brake on.
Complained when she got home that accelleration was a bit lacking, also put about 500,000k's on the floats brake linings :mad:

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Originally Posted by Iain

I found what buggers my fuel economy on my Cruiser is SWMBO towing the float with two TB's and the hand brake on.
Complained when she got home that accelleration was a bit lacking, also put about 500,000k's on the floats brake linings :mad:

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:D Well that will do it.:D

Al :D x a brazilion

Best economy is when you get the thing into top gear or overdrive in its recomended speed range , touch the breaks as little as possible use cruse controle , don't carry any extra weight , or roof racks, accellerate slowly , get picked up rather than pic up









Oh and pump you tyres up to a brazillion kpa,


The trouble with life is there's no background music.

If game, tuck in behind a semi and use their drag to pull you along. :rolleyes:

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Originally Posted by DavidG

Yes.
Air resistance is a square law.
Double the speed, four times the energy required to overcome the air.
Dropping the speed does improve fuel economy.
Try riding a motor bike to check out the air resistance.

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If you are doing 50 kms per hour no wind, and I go to 100kms per hour no wind.
How can the wind resitance be 400 kms per hour?

Al :confused:

AIR resistance Al, not wind resistance, thar's a diff-a-nance. ;)


The amount of power required to overcome a 100Km "wind" is 4 times greater to overcome a 50Km "wind".

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Originally Posted by Daddles

Don't forget, you save even more fuel if the boot is full of fishing gear and the cabin full of sand ... like mine :D

Richard

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That must be "Quicksand"...Ha!Ha!:D
savage(Eric):D

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Originally Posted by DavidG

If game, tuck in behind a semi and use their drag to pull you along. :rolleyes:

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Right in his blind spot.....just keep a close eye on those brake lights.....and hope like hell theyre working :D

kiwigeo
I did put "If game".
I am not but know of others that have :eek: and they say that they used very little fuel.

ozwinner
At 50kph your car moving through the air and causing the air to move around the car. This needs energy to do this.

At 100kph you car will consume 4 times as much energy as it did at 50kph.

This is why manufacturers try to reduce the air resistance of their cars.


ps: I always thought red cars went faster, and used less fuel, and ..... :D

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Originally Posted by DavidG

ps: I always thought red cars went faster, and used less fuel, and ..... :D

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only if yer got a foxtail tied to the top of your radio aerial :D

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Originally Posted by Cliff Rogers

AIR resistance Al, not wind resistance, thar's a diff-a-nance. ;) The amount of power required to overcome a 100Km "wind" is 4 times greater to overcome a 50Km "wind".

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I can hear the squeaky cogs of Al's grey matter turning over from here :D