Fuel consumption conundrum

[Greg_D]

i have an idle query based on highly subjective data.

Let me make it clear from the outset that i'm no fuel consumption bore, (i've never knowingly got more than 30mpg out of any car i have ever owned)

When i accelerate slowly and considerately out of a junction into an empty road, the light throttle fuel consumption of my volvo (as signified by the instantaneous fuel consumption computer) flashes up some truly horrific readings (little more than 10mpg driving like miss daisy up to about 60mph) but once up to speed it settles down to it's normal cruising mpg - about 25mpg, pretty quickly

surely it is better to bury the throttle, accept the 6mpg for a few seconds and then cruise as opposed to creeping up to speed. Surely it is more fuel efficient over the course of the journey to drive fast and get up to speed quickly???

[StottyZr]

Brisk acceleration has always been recommended for fuel efficient driving.

[pherlopolus]

Pulse and glide is the way to do it

[fizz47]

If often thought about this too...

On a similar note - what will give me better life of brake pads/ discs?


A) Gradually slowing down so the brake force you apply is less but for a longer period

B) Applying a higher amount of brake force so total period of time using the brakes is less..

[Boydie88]

I don't think it makes much difference.

Savings are to be had by maintaining momentum.

[Boydie88]

fizz47 said:

If often thought about this too...

On a similar note - what will give me better life of brake pads/ discs?


A) Gradually slowing down so the brake force you apply is less but for a longer period

B) Applying a higher amount of brake force so total period of time using the brakes is less..

Get off of your throttle even earlier so you don't use your brakes at all

[Amateurish]

Boydie88 said:

I don't think it makes much difference.

Savings are to be had by maintaining momentum.

+1 In theory, the amount of energy requied to get your car to the higher speed is the same, regardless of whether you accelerate over a short or longer period of time.

[chris182]

Amateurish said:

Boydie88 said:

I don't think it makes much difference.

Savings are to be had by maintaining momentum.

+1 In theory, the amount of energy requied to get your car to the higher speed is the same, regardless of whether you accelerate over a short or longer period of time.

Absolutely true. The efficiency of how the engine and drive-train converts fuel energy into kinetic energy (speed) is not constant though, hence the amount of fuel required to increase speed by a given amount does vary depending on how you drive. I think for an average petrol engine the most efficient engine speed range is 2000-3000rpm roughly, so the best method to accelerate economically is by using this rpm range (don't know about diesels).

I find that in my Clio it doesn't matter how hard I accelerate, the fuel economy remains resolutely good so I go flat out to the speed limit wherever possible. In my Mercedes however, driving like Miss Daisy does hugely improve the overall fuel economy.

[chris182]

doogz said:

chris182 said:

Absolutely true. The efficiency of how the engine and drive-train converts fuel energy into kinetic energy (speed) is not constant though, hence the amount of fuel required to increase speed by a given amount does vary depending on how you drive. I think for an average petrol engine the most efficient speed range is 2000-3000rpm roughly, so the best method to accelerate economically is by using this rpm range (don't know about diesels).

I find that in my Clio it doesn't matter how hard I accelerate, the fuel economy remains resolutely good so I go flat out to the speed limit wherever possible. In my Mercedes however, driving like Miss Daisy does hugely improve the overall fuel economy.

Being a passenger in your car must be lovely.

Oh I'm sure it is. Maybe I should have qualified that with wherever possible and sensible. I don't do full on smoking starts every time I'm sat at the lights in town.

[SturdyHSV]

The Monaro is like this. If you crawl to the speed limit, it drinks petrol. Blasting there the cruising is much more efficient.

I've had 29mpg skirting around a deserted Milton Keynes with this technique. Needs to be combined with coasting in gear instead of braking though.

[Chrisw666]

I've always found my cars are best on fuel when driven at constant speeds for a long time, to get the most out of my fuel I therefore drive further and refuse to slow down for anything or anyone.

[wormburner]

SturdyHSV said:

The Monaro is like this. If you crawl to the speed limit, it drinks petrol. Blasting there the cruising is much more efficient.

I've had 29mpg skirting around a deserted Milton Keynes with this technique. Needs to be combined with coasting in gear instead of braking though.

It's the last sentence that is key. getting 300m of free travel every time you need to stop makes a bigger difference than anything around town.