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

MushyPeas · 13 January 2008 at 10:25PM

charlieheard wrote: »

I'm very surprised that your consumption is higher on the motorway unless you're travelling significantly faster than 70mph. One thing that really kills fuel consumption (apart from high speed) is changing your speed. Slowing down for corners and junctions and speed limits around towns all mean that the car using energy to return to the cruising speed. So as well as being slower, non-motorways usually mean poorer consumption. Think of it like going the shortest route on a walk. You lose loads of time and energy climbing hills and descending rather than taking the smoother, longer path.

It also means that the shortest route is seldom the most economical, as it usually involves lots of junctions and minor roads. (Unless you're travelling on a bicycle, of course, where the cruising speed isn't very high, so distance is more important than cruising. )

Charlieheard, thanks for your input. I think I might have to do some more experimentation to find out if my fuel consumption is really changing. With the 'old road' vs. the motorway I really did find a difference with fuel consumption over 250 odd miles.

Tonight I travelled a shorter but 'windier' route home (20 mile trip), so logically your arguement about slowing down etc. makes sense! But one trip I do still ends up being on quite smooth roads (and a ferry...) so I am hoping that I am saving money as it saves around 8 miles per round trip.

I guess to find out the answer I'm really going to have to start tracking journeys, fuel consumption etc

anewman · 13 January 2008 at 10:34PM

LYNNIT wrote: »

I seen a product in the garage called Redex which is reputed to save up to 20% of petrol when it is put in the tank.
Does anyone know if this stuff works?

This cleans the injectors. It may improve efficiency, but only slightly, perhaps 5%. I certainly wouldn't expect anywhere near 20% improvement.

Ben1982 · 14 January 2008 at 12:21AM

I started trying to drive more efficiently starting last Monday. Have increased my onboard average mpg display (on my Diesel Primera) from about 33.6mpg to about 40.9mph (similar ~20% increase).

Will see how much this will save me in the long run, by how often I need to fill up (currently it's around the 2 week mark).

robin58 · 15 January 2008 at 3:36AM

When I used to work in London, I tried unsciencetific test on fuel consumption.

I drove to London on full tank 44ltrs, 1.1 car. over a week.

If I drove at 70mph, drove 'fast off' at the traffic lights and generally heavy on the accelerator , I used up more petrol.

IF I took it sedatelly, doing no more than 50mph, drove with consideration at traffic lights and took my foot off the accelerator I used less petrol.

I could and did save at least a one way trips worth of petrol over a week ( about 35miles). sometimes more. Add that up every week and it was big money. ( car ran about 11miles to the litre )

Pygmymonkey · 15 January 2008 at 11:52PM

A friend of mine has just bought a bio diesel reactor for his garage. £900 + VAT. Says that he can get cooking oil for free from local chippy (they have to pay to dispose of it) and he can make about 40L in 36 hours. total cost of 8p/L. Recent tax changes say you can make 2500L a year for personal use before you have to pay tax or duty. Can't remember where he got it from, i'll find out and post here tomorrow.
Unfortunately i've got a petrol car but the payback on one of these things would only be a year... worth thinking about getting a different car.

crossleydd42 · 16 January 2008 at 12:10AM

redpete wrote: »

56mph is often quoted because this is a standard used to give a common comparison point, it is not the speed at which cars exhibit the best mpg.

56mph is used because it is the highest speed one can travel at without incurring [significant] wind resistance. I usually push my driving up to 60mph as wind resistence is still not very significant. The difference in fuel consumption between 60mph and 70mph is very significant, though.

SingingDwarf · 16 January 2008 at 12:58AM

crossleydd42 wrote: »

56mph is used because it is the highest speed one can travel at without incurring wind resistance.

Absolute poppy !!!! :rotfl:

56mph may be the speed at which a vehicle incurs *least* wind resistance, but it will not incur *no* wind resistance at this speed! Wind resistance (or drag) is related to the square of the speed of the vehicle.

Olz · 16 January 2008 at 1:03AM

Driving economically is all about reading the road well ahead, and as Martin states road safety benefits too. I was taught the 'police system' of car control which utilises 'gears are for going and brakes are for slowing.
Some people are taught to drive by changing gears down in sequence to slow the car for a junction. This is not how to drive, it is how we learn to use gears when we are taught to use the clutch. We learn to drive after passing our test!
Using your head and slowing for the 'feature' and sometimes not even using the brakes but maintaining momentum will not even cause you to lose journey time. It is also cheaper to replace brake pads than it is to buy a new clutch.
If you go to a local advanced driving group, they will teach you these techniques, and if you pass the test, with some companies you will qualify for cheaper insurance. You will save fuel and there will be less wear & tear on your car and we will all be safer. I am not connected in any way with adv. driving groups or schools. I am now climbing off my soapbox!!
OLZ:cool:

Jay.992 · 16 January 2008 at 1:23AM

:T I spent many years driving a white van with all my fragile work kit in racks in the back. You soon learn to drive carefully when you have to spend hours putting a few hundred small item back in boxes and racking bins.
The habits stay with you and when in your car the drive is far more comfortable for passengers as they don't get thrown about.
It is right you can drive quickly without driving fast, we had to do that all day long or we got nothing done.
Although my wife is a good and careful driver I can always get a better fuel return than her, she says that I drive faster than her but as I say - quickly not fast.
The other week we were in lengthy traffic and I must have only used my brakes once for every ten of the cars in front. I like to keep a sensible distance so that I can allow my car to slow more naturally, when the brake lights on the car in front of the obe in front come on I take my foot off the gas. When they race off I let the engine pick up speed gradually - quickly but not fast. We always caught up easilly without leaving large gaps for other to leap into. To sum up, when at work I had to drive 250 miles to a company do, two of us left together in separate vans, I drive like described above my colleague raced off changing lanes and running about flat out. I arrived five minutes behind him and I got back on the same tank of fuel but he had to fill up before setting off back!

AHAR · 16 January 2008 at 1:51AM

crossleydd42 wrote: »

56mph is used because it is the highest speed one can travel at without incurring wind resistance.

No resistance?! :rotfl:Next time you're going at 56mph pop your hand out the window. Feel it?

When Jeremy Clarkson got that diesel Audi from London to Edinburgh and back on one tank he seemed to be trying to keep the car at the lowest speed it would smoothly go in top gear so maybe that's a good approach to take.

I find the constantly changing current fuel consumption display on my car too distracting - I keep looking at it willing it to get better! I leave the display on outside temp. instead.
A far more effective way for me to improve fuel economy is getting out of bed earlier and missing the worst of the queues on the way to work!

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

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