I have a C4 VTR+ 1.6 (110) diesel.
I try to drive in (what I believe is) the most economic fashion. i.e. don't race away, into 3rd at about 20mph, 4th at 30mph, and 5th when it doesn't feel laboured.
Car has done nearly 6000 miles from new. Can't better than 37mpg round town. In addition, can't better than 55 on a run sticking to the 70 mph on a motorway (where I use cruise control) Aircon is usually on.
Are my expectations too high?
|
My 3.0litre E46 could manage that !
--
735310 - Total sense in an upside down world.
|
Is that a 330d or i pug?
My Ford Ka can average 52mpg on a good motorway run keeping to 70mph.
--
Its not what you drive, its how you drive it! :-)
|
d
--
735310 - Total sense in an upside down world.
|
See the possible explanation as to why:
tinyurl.com/nzju3
- - - - - - - - - - - - - - - - - - - - -
What\'s for you won\'t pass you by
|
|
|
|
Very much doubt you will see better during its run in,it also is about the same for diesels going back some years.
cruise control doesnt do anything different to using your foot on pedal/apart from automating it ie you dont need to use pedal.
give it 40k miles and you will see the difference as older diesels
--
Steve
|
The slow getaway theory is complete and utter twaddle.
You should accelreate at peak torque for your car, which will initially feel fairly brisk. This has been found experimentally to use the least fuel over a complete journey.
V
|
So why do all the test drivers who specialise in getting high MPG all state that brisk acceleration eats fuel.
------------------------------
TourVanMan TM < Ex RF >
|
Because they are wrong.
What they confuse, like most people, is instantaneous fuel consumption versus overall consumption. Look at an instant fuel consumption gauge and it looks like you're saving fuel accelerating slowly. Thus, people now dawdle everywhere. What actually matters is overall consumption.
In light of this, getting to cruising speed quicker will leave more time at constant speed. The initial acceleration's increased consumption is more than balanced out by the reduction due to spending more time at cruising speed. Unfortunately, this is counter-intuitive given the instantaneous consumption recorded by the devices being used.
For real research results: http:// tinyurl.com/oalj
or another version at: tinyurl.com/el7g3
I've named my source - who are your "test drivers who are specialise in getting high MPG"?
V
|
Stuart Bladon (who held the UK economy record for a production car) in an article about how he drove a vehicle on the contents of a standard fuel tank ( 17 1/2 GALLONS ) for 1,338 miles in an Audi 100 TDi
Unfourtunately there does not appear to be a web reference for this article.
There also does not appear to be too much in the way of scientific evidence backing up that single claim from a single experiment and a single source you quote. The sheer laws of physics would dictate that to accelerate an object faster requires more power, more power requires more fuel.
I can see the school of thought that says there must be a crossover point where more fuel x shorter time < or > less fuel x longer time. However in real world driving where its all stop start most of the time, I dont think your argument stacks up. Accelerating "briskly" from traffic light to traffic light will eat fuel.
so there ;-P
------------------------------
TourVanMan TM < Ex RF >
|
I tend to just accelerate "normally" (keep with the flow of traffic), try to keep the rev counter around 2,000-2,500 RPM when cruising, and take advantage of the almost complete lack of high gear engine braking to "coast" or use only miniscule throttle openings on the motorway.
This gets me anything up to 46 mpg in the Mondeo, a car which many other owners I've spoken to only get high 30's from.
|
Don't accelerate hard up hills.
Don't acclerate up hills.
Best tip I know.
madf
|
I watch a motoring prog some years ago - the item covered a couple of journos taking a Golf diesel (Mk3 from memory) on an economy challenge from London to somewhere 200 or so miles away, using a set route, mixed roads, with other competitors who were "expert" economy drivers. They tried driving for best economy within the the traffic, and got XX mpg. On the return they drove normally, and got almost the same.
I drive a 405 TD estate with 169k, and keep up. It gives 45 mpg overall, using mostly rural roads.
|
|
|
|
"The sheer laws of physics would dictate that to accelerate an object faster requires more power, more power requires more fuel."
I agree absolutely.
"I can see the school of thought that says there must be a crossover point where more fuel x shorter time < or > less fuel x longer time."
Try a "thought experiment" (if it's good enough for Einstein, it's good enough for me). Imagine an extreme case where you have a car that cruises at 30mpg. If you accelerate at full whack, this drops to 1mpg. If you accelerate gently enough, it will only drop to 29mpg. Sounds like gentle acceleration is the answer.
The problem is that you don't know how long you will be accelerating, so if the full on gets you to cruising speed in, say, one second, while the other takes 20 minutes (see, I told you I was looking at the extreme case) then it would make sense to accelerate hard. SO, there clearly IS a situation where it makes sense to accelerate hard in order to improve *overall* fuel economy.
"However in real world driving where its all stop start most of the time, I dont think your argument stacks up."
On what basis?
" Accelerating "briskly" from traffic light to traffic light will eat fuel."
I agree. What matters is not how much fuel you use accelerating away from the lights, but your overall consumption. That's what everyone seems to miss.
V
|
IAM drew my attention to block changing - miss out second or third. Not sure if that would help during acceleration cycle.
And anticipation of braking - try not use use brakes at all (by reading the road ahead correctly, rather than driving dangerously!!) and control your speed using your right foot. Especially good at large roundabouts - look early, judge your speed and go for your gap - hopefully avoiding coming to a complete stop (which many people do even on an empty roundabout).
|
IAM drew my attention to block changing - miss out second or third. Not sure if that would help during acceleration cycle. And anticipation of braking - try not use use brakes at all (by reading the road ahead correctly, rather than driving dangerously!!) and control your speed using your right foot. Especially good at large roundabouts - look early, judge your speed and go for your gap - hopefully avoiding coming to a complete stop (which many people do even on an empty roundabout).
Completely agree with your braking comment, but with regard to acceleration, surely it makes sense to keep the revs as close to peak torque as possible for maximum efficiency (i.e. maximum accelerative effort for minimal throttle opening).
Can't see how that would be possible with block changing, meself.
Cheers
DP
|
|
|
|
Which presumably is something to do with why fuel consumption computers always read optimistically.
If a car does 30mpg then flooring it from the lights could probably only take the fuel consumption down to 10mpg for a few seconds, whereas cruising to a halt trying not to use the brakes can take the computed consumption upto 1,000mpg or more while it is still moving without using fuel.
|
"Which presumably is something to do with why fuel consumption computers always read optimistically"
Most, if not all have an "out of range" parameter. This means in the real world that its says "1000mpg? cant be right, dump thats till we reach sensible levels. Where that sensible level is tho is a different matter and yup I can quite easily see a spurious 99mpg being fed into overall equation. Certainly seems to be that case that all car average fuel consuption computers over read by some margin
------------------------------
TourVanMan TM < Ex RF >
|
>>fuel consumption computers over read by some margin
I can't imagine any manufacturer being dumb enough to install a pessimistic one! Imagine the warranty claims - "my handbook says X, but the car's computer only says Y"
Number_Cruncher
|
|
|
|
|
|
|
|
I have the same engine in a 307 and, according to the computer, I am getting about the same figures as you. I don't drive around towns but cross-country and driving gently I can get 60 mpg and on an A road or dual cariageway run, not going over 75 I can see 55 mpg. As discussed elsewhere the consumption will vary with season/temperature. I see a reduction of about 3 mpg in the winter.
|
The argument for brisk acceleration maximising the run time at an economical cruising speed sounds plausible, but only if you are certain of being able to maintain that speed having briskly got there. It is not the same as accelerating briskly all the time, and then throwing it all away by having to brake at the next set of lights. If you know there is a pretty sure chance of having to slow down again very soon, surely intuition is right - save the fuel, save the braking?
But I see the sense in accelerating along the slip road and then maintaining a constant 70 for the next hundred miles.
|
|
I discovered that there's little or no difference in my car (Xsara 1.9TD) whether I drive really carefully or just thrash it everywhere.
|
|
Well you are lucky if it doesn't affect the fuel consumption! What about tyres, brakes, you and your passenger's nerves!
|
Stuart Bladon (who held the UK economy record for a production car) in an article about how he drove a vehicle on the contents of a standard fuel tank ( 17 1/2 GALLONS ) for 1,338 miles in an Audi 100 TDi Unfourtunately there does not appear to be a web reference for this article.
tvm - there are references to at least two cars he drove:
www.dieselcar.com/pdf-files/articles/power/power07...f
Economy driver Stuart Bladon took the 1992 Audi 100 TDI to an amazing 75.9mpg ....
www.ukcar.com/guinness/index.html
In 1989 Stuart Bladon drove a Citroen AX 1.4 DTR 112 miles 18 yds on one ......
the first one refers to "Bladon's soft foot".
|
|
|
|
Perhaps I should redefine "thrashing" to mean "driving briskly." It feels like thrashing because I'm a mechanical hypochondriac. :)
|
Sounds to me like you're changing up too early. When accelerating you want to rev the engine to around 2500RPM so that when you change up the revs drop to around 1750-1800RPM which is around peak torque. When crusing, you want to maintain above 1700RPM - anything below that and you'll be planting the throttle whenever you want more power which will use more fuel. Anticipation makes a big difference - hold back from the car in front and come off the throttle at the first sign of slowing down rather than waiting and then using the brakes. If you're foot is off the throttle and you're moving in gear you are not using any fuel at all!
You won't see the best economy until you've got at least 15k on the clock.
|
|
|
|
|
Didn't Adam go into this in some depth and come to the same conclusion (with supporting input from onlookers)?
JH
|
|
|
|
"It is not the same as accelerating briskly all the time, and then throwing it all away by having to brake at the next set of lights."
Brief experiment in the Jag tonight, so we're talking about a 2.5 petrol engine.
Accelerated at roughly peak torque and looked at my instantaneous fuel consumption; it was pretty much around 11-13mpg. Accelerated to 35, then coasted up to the lights at red. Another estimate here - I reckon I accelerated for about a quarter of the distance to the lights. This leads me to think, x yards at 12mpg, 3x yards consuming no fuel at all - thanks to fuel overrrun cutoff - gives an average over that distance of 48mpg.
Now, I was clearly experimenting - normally I'd have a drift of throttle on to keep up the speed, but the principle is there. I don't reckon there's any degree of slow acceleration that would have my car doing 48mpg. The interesting point, of course, is that someone just looking at instantaneous fuel consumption would see 12mpg and have a dicky fit, despite the fact that the overall mpg was in the region of 48 (and I accept there are a number of estimates in the above).
I also agree with your comment about the brakes. Keeping off them is probably important. What did it here was using the overrun.
I'm interested in this now. I may do more real world experiments.
V
|
I would just like to point out two great pages to check on this subject, a matter close to my heart having to fill a 2 litre focus!
money.howstuffworks.com/how-to-drive-economically....m
auto.howstuffworks.com/question477.htm
My personal best is an average 50.4mpg over 35.1 miles (about 26 miles M4 motorway, rest town).
My continental eco contact tires help, as does following articulated lorries on motorways (the correct safe following distance - you shouldn't be able to read their numberplate!, and you will be amazed at the difference the slipstream makes to your consumption).
Pretend the accelerator pedal is an egg and don't stamp on it or you'll mess up your carpets!! and avoid the brakes at all costs, they are only there for emergencies, use your engine and excellent forward planning to slow.
Air con also makes a huge difference to consumption, working the A/C on full cool on a hot day will see 6-8mpg dropping off.
|
|
|
|
|
|
