'Petrol efficiency experiment; an increase of 20%' blog discussion

tomstickland

I'm well on target for 38mpg or maybe even 40mpg from my 1991 BMW 318iS (1.8 16v). That's for cross country B road commuting (hilly) for a few days, two motorway trips and driving round Bristol and Cheltenham in busy traffic. I've done at least one foot-to-the-floor overtake on each commute journey too.

I've generally been accelerating at about half throttle. My biggest savings have come from backing off the power a lot earlier for slow points (allowing the car to gradually slow whilst still in gear), avoiding stopping at all costs, and lowering my cruise speed on the motorway from 85 to 70. Planning ahead allows a near constant speed path to be plotted through the middle of typical jerky traffic.

I've done a lot of thinking about this. I don't think that cautious acceleration helps much - if you wish to accelerate from 20 to 60 then it will take a certain amount of energy to do so, and doing it in 15s versus 45s doesn't make a huge difference.
However, it is throwing energy away by braking that is where the savings can be made.

Tojo_Ralph

pault123 wrote: »

A quest should you choose to accept it on tomorrows commute - radio, aircon and headlights ON but keep the "gear change thingy" happy and let me know what mpg you average?

For every ying there is a yang... The journey in today recorded under the same conditions as last night c/w traffic and against the lie of the land resulted in the following figures...

42.8mpg... Ave Speed 22 mph... Time 31 mins... 11.5 miles

Which is a good bit down on last nights figures travelling in the opposite direction...

50.4mpg... Ave Speed 34 mph... Time 20 mins... 11.5 miles

I don't know how much longer I can last without music... .... And I want to test the radio fuel consumption theory, so tonight I will go with adding in music as the only variable to see what difference that makes and if we are going to get really technical, cranking up the tunes will mean powering fourteen speakers, ten amplifiers and a Digital Signal Processor.... So it should provide a good indication of whether or not the radio makes a difference to fuel economy.

pault123

Tojo_Ralph wrote: »

For every ying there is a yang... The journey in today recorded under the same conditions as last night c/w traffic and against the lie of the land resulted in the following figures...

42.8mpg... Ave Speed 22 mph... Time 31 mins... 11.5 miles

Which is a good bit down on last nights figures travelling in the opposite direction...

50.4mpg... Ave Speed 34 mph... Time 20 mins... 11.5 miles

I don't know how much longer I can last without music... .... And I want to test the radio fuel consumption theory, so tonight I will go with adding in music as the only variable to see what difference that makes and if we are going to get really technical, cranking up the tunes will mean powering fourteen speakers, ten amplifiers and a Digital Signal Processor.... So it should provide a good indication of whether or not the radio makes a difference to fuel economy.

10 amps! :rotfl::beer:

redux

You can get some good ear defenders for under £20, if the volume ends up too loud :rotfl:

golders

Thanks for all the great tips on gentle considered driving. I have found it really makes a difference too. Even my old Nissan 100nx is doing 44mpg (not bad as its supposed to do (35mpg combined).

I have also been using this Miles per Gallon Calculator to work out the correct MPG.

www.mpg-calculator.co.uk

Tojo_Ralph

redux wrote: »

You can get some good ear defenders for under £20, if the volume ends up too loud :rotfl:

Volume and clarity is where it's at ... and anyways, so the blurb says, to address the issue of a uniform volume, an integrated microphone is fitted between the two front seats and continuously measures changing noise conditions (tires fitted, rain on windscreen, wives, bleating kids, etc) and instantly adjusts the output sound to ensure a uniform acoustic experience..... What we don't know yet though is if it sucks the juice out of the tank.

pault123

Tojo_Ralph wrote: »

Volume and clarity is where it's at ... and anyways, so the blurb says, to address the issue of a uniform volume, an integrated microphone is fitted between the two front seats and continuously measures changing noise conditions (tires fitted, rain on windscreen, wives, bleating kids, etc) and instantly adjusts the output sound to ensure a uniform acoustic experience..... What we don't know yet though is if it sucks the juice out of the tank.

does it wash the pots as well? :T

Tojo_Ralph

pault123 wrote: »

does it wash the pots as well? :T

The equipment I have for pot washing is far less sophisticated, a lot older, far more temperamental and to be honest with you, I really don't know why I am still living with her?

tinbucket

harryhound wrote: »

Guess the speed that gets the most cars down a stretch of road in a given time?

If a stop and start and slam on the brakes crash test dummy causes a "ripple" the speed falls below this magic number and a traffic jam then develops. Not to mention the number of tailgating drivers who then have near misses or worst "kiss" bumpers, putting a lane out of action for a good 20 minutes.

Harry.

here here. I travel around 35k a year mostly on motorways and I have lost count of the number of tailgating idiots or lane hoping under cutters who I've seen cause accidents... it's a mind set. if I drive like a bat out of hell, i'll get there quicker - of course you will! and what will you do with all those five minutes? spend them in the forecourt filling up of course, or in a tyre garage getting your tyres changed from all the excess wear. The aim is to find the speed at which you use the least fuel for the given journey, for a reasonable time spent driving.

Tojo_Ralph

So here are my driving home figures with the tunes cranked up. I didn't really get the traffic and had to gun the car a couple of times to pass slow moving vehicles.

To... Ave 41.5 mpg... Ave Speed 23 mph... 31 mins... 11.5 miles. Tunes On
From... Ave 46.3 mpg... Ave Speed 32 mph... 21 mins... 11.5 miles. Tunes On

To... Ave 42.8mpg... Ave Speed 22 mph... Time 31 mins... 11.5 miles. Tunes Off
From... Ave 50.4mpg... Ave Speed 34 mph... Time 20 mins... 11.5 miles. Tunes Off

That said, I don't trust the figures at all and just know that when I fill the tank and do the sums I'm going to see an average of 40 mpg, which is well down on the 51.3 mpg published Ave Combined. I'll wait until I get more miles on the clock before drawing conclusions.