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

steve6375

Has anyone mentioned 'digital driving'?

Whether you have your foot down by 1/4 or 1/2, the difference in mpg is only small (say 10mpg), but if you take your foot completely off the accelerator then the difference is at least 100mpg!

As has been mentioned before, when you take your foot off the accelerator, the engine management units effectively cuts off the fuel.

I have a new Vectra 2.2SRi - no matter how carefully I drove to work, doing no more than 50mph, with a 10 miles journey on B roads, I would get 26mpg (!!!!). I tried many things to improve this but to little affect. I am a careful driver and not at all heavy on the pedal!
I tried the 'digital' method - accelerate mildly (about 1/4 to 1/3 on accelerator) up to my required top speed (55mph), then take my foot off the accelerator completely until I slowed down to just about 30mph (i.e. the slowest I could go and still keep in top gear), I then repeated this and accelerated up to 50mph again. Obviously you only do this on fairly flat roads and downhill.

I got an increase from 26mpg to 30mpg - better than 10% or 10p per litre - not bad!

I tried just going at 40mph all the way (where possible) and I got 26mpg again. Then went back to digital driving and got 30mpg again.

So it really works. Some side effects are:
1. It's really annoying/uncomfortable to drive like that!
2. Cars behind you tend to keep their distance because you keep slowing down. So only do this if it is not too busy.

This is effectively driving in neutral but it is legal and safe. So reasonably hard acceleration is OK, as long as you then 'coast' with your foot off for a good length after that. The average of doing this is less than if you just kept your foot at 1/4 all the way.

Idiophreak

steve6375 wrote: »

Has anyone mentioned 'digital driving'?
no matter how carefully I drove to work, doing no more than 50mph, with a 10 miles journey on B roads, ...I tried the 'digital' method - accelerate mildly (about 1/4 to 1/3 on accelerator) up to my required top speed (55mph), then take my foot off the accelerator completely until I slowed down to just about 30mph (i.e. the slowest I could go and still keep in top gear), I then repeated this and accelerated up to 50mph again.

I always wondered what the weirdo's in front were up to, making me late for work...maybe this is it.

Have you thought, perhaps, about buying a car you can afford to run and keeping up with the flow of traffic?

In reference to this thread, generally, though - I had a debate with my parents about whether it would actually make as much difference as Martin claimed, so decided to do an experiment.

My first tank, I drove normally (and I do have quite heavy feet) - got about 330 miles out of a 45-50l tank.

The second tank, I drove "granny style" - shortshifted all the time, cut 10-15mph off my top speed, careful not to rush too much (except to overtake "digital drivers", obviously ), cut down on engine breaking - got 430 miles out of the tank.

Needless to say I've learnt my lesson - if nobody's waiting for me, I keep it granny style - and just imagine the pounds I'm saving...

tomstickland

baileypl wrote: »

- use downhill to gain momentum then go uphill on feathered throttle( many people brake downhill then accelerate uphill)
- keep momentum round corners rather than brake, where safe to do so
- adjust speed coming up to roundabout or traffic lights so you don't need to stop
- on busy motorways use middle or inside lanes mainly as outside lane suffers from concertinaring which involves braking then acceleration
Hope this helps!

I agree with this, however, on busy motorways just use whatever lane is available, try to maintain a constant speed, if yo-yo traffic is encountered than back off early and try to smooth the yo-yos out.

I have to laugh at the randomness of some drivers: I travelled abour 40 miles at 70mph indicated the whole way and managed to leapfrog someone. They came flying by after following me for a while in the outside lane, big acceleration run etc. Then about 2 miles later they were in the middle lane following a lorry and I overtook them.

I've discovered that maintaining a near constant speed or avoiding stopping at all costs is actually pretty entertaining.

I agree that there is a requirement to consider those behind you. I've found that at 60 indicated on the local twisty road I'm showing 50mpg and I can drive most of the road at that speed with no big issues. It's very frustrating to encounter the local "40 everywhere" vehicles and I actually lose mpg because of them, either due to their unpredictable braking or when the opportunity comes to overtake them.

steve6375

The other people that cause loads of pollution and traffic jams are ...... cyclists!

Yes, on a narrow country road, why do these 'green' lycra-clad maniacs who insist on cycling in the in a wibbly-wobbly way all over the lane, think they are being really 'green'?

The nice quiet bloke on his way to work, pedalling slowly at the side of the road and politely keeping as far left as he can to let cars pass is fine. But these lycra-clad twits should be banned. And it gets worse in the summer!

I always know when there is one on the road, there is a large queue of traffic trying to overtake but cannot because of traffic coming in the opposite direction and the very wide clearance you have to give them!

Some even insist on riding in the middle of the road ('look at me I am doing 25mph - aren't I cool!') when they know you and 30 other cars and trucks are stuck behind them.

I wonder how much pollution and expensive fuel does just one cyclist cost the world?

Can we ban lycra cycle shorts please?

maudred

MushyPeas wrote: »

Interseting post as I've been thinking a lot about fuel consumption. I travel a lot between SWest and London. I noticed that if I took the motorway my consumption increased (driving around 70 mph) whereas on the 'old road' up it was averaging 60mph so was more fuel efficient.

Also I purchased a tomtom last year. I keep experimenting with the 'shortage' route versus the 'fastest' route. Sometimes the time different isn't much but I save around 5 miles in distance. Though in the country you do end up going down some little roads! Has anyone else tried this method to save mileage?

My next plan is to calculate how much it costs me to drive a mile, will get around to that soon

I guess it would depend on how much you were sitting in queues on the motorway, depending on what time of day you were travelling ie you may have been able to maintain 60 mph on the less busy roads more than you could maintain 70 on the motorway. Like someone has said in another post, changing speed uses more fuel. The motorway is the best way to go if there is hardly any other traffic but if you have to start waiting to change lanes then flooring the accelerator to take advantage of a gap etc it is probably gonna use more fuel.

maudred

Another thing to take into account might be the wheel alignment. Appologies if someone has already posted about this, i didn't have time to read the whole thing. If the wheels aren't aligned properly the tyres wear more quickly and unevenly. You are basically stearing slightly sideways to compensate but you don't notice it. This obviously means the tyres need replacing more often so there is a saving to be there, but i would guess it would cause greater resistance too.

Does anyone have any info to confirm whether this is the case and how much the fuel efficiecy could be affected?

harryhound

steve6375 wrote: »

The other people that cause loads of pollution and traffic jams are ...... cyclists!

Yes, on a narrow country road, why do these 'green' lycra-clad maniacs who insist on cycling in the in a wibbly-wobbly way all over the lane, think they are being really 'green'?


Can we ban lycra cycle shorts please?

Here speaks a motorist, who I bet has not made a 15 mile cycle journey in the last 10 years?

Cyclists block lanes because it only takes one idiot to swipe us with a wing mirror and we are likely dead.
I've seen dead cyclists but I've yet to see a motorist killed by a cyclist.
The majority of car journeys are less than 5 miles so get on your bike.

Harry.

steve6375

Hi Harry

I used to cycle to work every day for 20 years (and in that time I was only knocked off my bike twice by cars and squashed by a bus that failed to signal left once). However, you are correct in that I have not cycled to work in the last few years as I now live more than 10 miles from work. Also my need for two total hip replacements have impeded my cycling somewhat!

I am not against cyclists - far from it - I am against these unthoughtful lycra speed merchants on their racing bikes that wobble all over the road whilst 'powering' along the road and cycle in the middle of the road lane even though they are fully aware they have a queue of traffic behind them. It is not just unthoughtful it is rude and environmentally unfriendly too!

steve6375

Reply to IdioPhreak

What I am saying is that 'granny' style driving is not the most fuel-efficient way to drive.
If you drove at 65mph on a motorway and then took your foot completely off the accelerator until you reached 55mph and then accelerated up to 65mph again (assuming a flattish road, not going up a hill and assuming it was safe to do so) you will get better fuel economy than just driving at 60mph all the way because you have 'coasted' for a lot of your journey at well over 100mpg .


Try it. i.e. try to take your foot completely off the accelerator whenever you can (but keep in top gear) and don't worry if you have to accelerate up to top speed again after a few minutes as you have saved a lot more fuel coasting than you used to accelerate.

Obviously consider other road users when you do this!

bigpat

I haven't read all eight pages of this thread, but does anyone else use neutral rather than potentially wearing out their clutch for "coasting"? I've only been doing this for about six weeks now and already i'm seeing approx 15% extra mileage out of my tank of diesel (2.0L Vectra 04 reg).

If I'm on the dual carriageway and traffic is light, I will smoothly get my speed up to about 70 and then pop it in neutral. The rev counter drops back to idle speed, but my speed stays the same for ages. I've travelled nearly a mile before my speed goes under 50 and other motorists are free to overtake if they wish. Equally, even around town, I've started to think ahead more and if I see I'm going to come up on a queue of traffic or if I need to slow for a roundabout or stop at a give-way, I'll slip it out of gear in good time.

All the while being MORE aware than I ever was before of what's in my rear-view mirror, so that if I need to speed up I can put it back in fourth or fifth, depending on what speed I'm coasting at.

And if I should come to the top of a steep hill, then I just need to nose it over the top and gravity will do the rest.


Last week I even overtook someone while I was doing sixty in neutral. It felt just great knowing that I was probably burning less fuel than he was. Two minutes before that I'd been overtaken by some nutter doing at least 100, and then watched his brake-lights light up as he approached the roundabout. I reckon he got to it maybe five seconds before I did and then I could hear his engine over mine as he floored it again. I bet his journey cost a lot more than mine for a few seconds spared.

I haven't tried any of this on a motorway yet, as it's generally rush (crawl) hour, so you don't get much momentum in the first place.

I learned a lot of this stuff during the 2000 fuel strike. We had just arrived in Cornwall for a weeks holiday from the midlands and had planned to drive about a bit. We knew we needed half a tank to get home, so we drove VERY sparingly while we were down there. And we noticed most other drivers wewre doing it too. I recall dawdling along at 40 in the inside lane of a dual carriageway and even though traffic was reasonably heavy, almost no-one was overtaking.

Ever since then I've stopped thinking about miles per gallon and instead measured it in miles per tank. And recently I have consistently got well over 500 from my tank, sometimes 520, whereas it was always under 450 before.

And now, my thinking has moved on again, to "miles per pound". I worked out a few months ago that (on average) every eight miles I drove cost £1. But now I'm sure I'm getting well over nine and possibly ten. It will need to be averaged out over a few months though.

Cycling and walking help too!:D