Having just read the some of the sites linked to from the other thread about how economical could a car be made, I found the following quotes to be of interest:
"completed the 330 mile event using just 19.12 litres of petrol to return an overall fuel consumption figure of 78.39 mpg. This is an improvement of nearly 28 per cent over the official combined figure."
"A later event involving three identical Toyota Avensis 2.2-litre petrol cars underlined the effect drivers have on fuel consumption. An IAM driver and a fleet manager both achieved around 56mpg, while a Silverstone instructor briefed to drive aggressively managed only 18mpg!"
I've seen many people on this forum complain that their car doesn't return the quoted MPG figures, I think the above backs up the arguement that those people are not getting good mpg becuase they have a poor driving style for economy.
It's a shame those sites don't give more details as to how they achieved those results.
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I am currently beating Volvo's claimed combined figure for the S60 by 8-10% doing almost all long motorway journeys, but in often heavy traffic which can be stop/start for an hour or more.
I can almost halve the claimed figure quite easily too. Driving style is everything.
Cheers
DP
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I think the above backs up the arguement that those people are not getting good mpg becuase they have a poor driving style for economy.
More to do with the fact that manufacturers figures have to be collected under laboratory conditions, and none of us drive round laboratories ?
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I calculate the average consumption for each month and without trying I consistently get better than the official "Combined" figure in my 03/03 2 litre Focus.
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Quite by accident, I opened the U.S. D.o.E. website on vehicle economy for 2008. They are quite explicit that the numbers are from laboratory tests and for comparison use only. They do go on to give a range of MPG within which a reasonable driver should achieve.
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Re Driving style
I was looking at the new model Xtrail to replace the one I've got. I mentioned to the dealer that it uses about 6.8 litres/100km, which goes up to about 11.5 or 12 when towing the caravan. Dealer's reply: "Some people use more than that solo"
Edited by Mchenry on 22/05/2008 at 12:47
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U.S. D.o.E. website on vehicle economy for 2008. They are quite explicit that the numbers are from laboratory tests and for comparison use only.
TBH I blame the press over here for plugging the figures without actually mentioning how they have been calculated and the reasons why they do them - the motoring press are as bad as the rags for it - that has raised expectations in the typical "layman" type of car buyer and now the manufacturers are reaping the whirlwind - perhaps HJ could explain why they do it as it makes the press look just as much idiots as the manufacturers.....
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It amazes me how many people complain about their cars economy without considering the way they drive is part of it. After all techniques to get good economy are neither complex nor shrouded in secrecy. The only thing about it is that it is much harder to drive economically than it is to drive fast. Anyone can put their foot flat, change up at the redline and stand on the brakes to slow, but to keep a fluid smooth motion going seems to be far more challenging for most. A good example is each day on my way to work I do about 5 miles in a 30 limit. I do it in my TT at 30mph on cruise control. Each day I will have someone right on my tail so close I can't see the bonnet, never mind the number plate. Thing is though, when we come to roundabouts I generally am able to avoid braking by adjusting my speed slightly (up or down) to fix with the gaps in the traffic. Mad max/maxine behind stops and then looks to see if it's ok to go. The amount of fuel people waste trying to go as fast as possible when it's straight and then waste momentum on the corners just amazes me. Then there's the ones that accelerate to the back of the traffic queues... why?
People can have as much lousy fuel consumption as they are prepared to pay for, me? I'm happy in my 40mpg sports car.
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I've beaten the quoted mpg on my 2006 Cooper convertible EVERY time I've filled it up. No matter how hard I drive it it will not got below 38 mpg, last tank was over 42mpg and thats with some spirited driving. Brilliant car.
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Beating or at least matching the manufacturers quoted MPG is easy.
Impatience, poor judgement and poor driving technique is what produces poor fuel economy for many a driver.
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Beating or at least matching the manufacturers quoted MPG is easy. Impatience poor judgement and poor driving technique is what produces poor fuel economy for many a driver.
I wouldn't necessarily classify it is poor judgement. Some people just like to drive.
I gave it a go last time I got in my car. I was slightly perturbed to learn that my friend was getting 30mpg in his S80 2.9 to my 24mpg in my 2.5T.
So I decided to take it super-gentle, and over a 12 mile round-trip, to Brooklands. 40 mph and 30 mph roads, with two large roundabouts, three mini-roundabouts, and two sets of traffic light. I used the cruise control even at 30mph, kept below the speed limit where I'd usually proceed more briskly, avoided stopping at most of the junctions, etc.
I got 27.9mpg where I'd probably normally get 21. But I wouldn't say my driving was better or safer, probably slightly less so if anything, I have more control at 2500rpm than 1500rpm
Obviously if I went along the motorway at 50mph for an hour or so, I'd do better.
That said, I don't do many miles. Perhaps 4000 a year. I could perhaps save 25 gallons a year by driving like a nun, and getting 30mpg rather than 25mpg.
I'm not going to sweat it. The £125 extra will make my journey my enjoyable and swifter.
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was better or safer probably slightly less so if anything I have more control at 2500rpm than 1500rpm
I don't follow why you would have more control at 1500rpm, to 2500rpm?
I wouldn't necessarily classify it is poor judgement. Some people just like to drive.
Also why is driving fast classed as "driving" whereas driving economically not? As said before there's just as much skill involved - in fact more skill if the antics of the typical boy racer is used as an example of "fast" driving!
Speed isn't everything, you know!!
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>> was better or safer probably slightly less so if anything I have more control at >> 2500rpm than 1500rpm I don't follow why you would have more control at 1500rpm to 2500rpm?
At 1500rpm the car has less acceleration to respond to situations. It will use more fuel at 2500rpm but has
>> I wouldn't necessarily classify it is poor judgement. Some people just like to drive. Also why is driving fast classed as "driving" whereas driving economically not?
It is not driving fast necessarily, more accelerating. I can pull off at the lights and accelerate hard to say 40mph, without ever actually driving fast.
As said before there's just as much skill involved - in fact more skill if the antics of the typical boy racer is used as an example of "fast" driving!
Well there's certainly skill in conserving momentum. It's just not much fun.
There's plenty of choices: go at 30mph rather than 50mph, because the next junction is 3/4 mile ahead, coast up to the lights rather than brake, etc.
Just not much fun.
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>> I don't follow why you would have more control at 1500rpm to 2500rpm? At 1500rpm the car has less acceleration to respond to situations.
If you are reading the road properly I'd sugest this isn't an issue, either that or I've been very lucky over the years I've been driving for economy and smoothness rather than racing!
It's just not much fun.
To you, obviously, but not everyone has the same views, some of us enjoy driving economically (and thats not just about conserving momentom!) just as much as you enjoy hard acceleration - everyone to their own...
Think you've also explained why your mpg figures are so low as well! ;)
Edited by b308 on 23/05/2008 at 17:57
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So I decided to take it super-gentle and over a 12 mile round-trip to Brooklands. 40 mph and 30 mph roads with two large roundabouts three mini-roundabouts and two sets of traffic light. I used the cruise control even at 30mph kept below the speed limit where I'd usually proceed more briskly avoided stopping at most of the junctions etc. I got 27.9mpg where I'd probably normally get 21. But I wouldn't say my driving was better or safer probably slightly less so if anything I have more control at 2500rpm than 1500rpm
It's not about going slowly either, it's about consistency. On my 10 mile commute through Bristol I usually average 30-35mph (half 30 limit, half 60 limit) while on a motorway trip I usually average >60mph without exceeding 70mph.
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My impression is that it is easier to do in petrol versions than diesel versions.
I have a 1.8 123hp Mondeo, stated mpg 37.2, actual 38 - 39mpg.
My mate has a 2.2 Dci 150hp Laguna stated mpg 47, actual 38 mpg.
We drive the same route only difference is he powers up hills on full throttle and I take it gently, but on the flat driving style is the same.
Have read many messages on this site where some diesel car owners have struggled to get any where near published mpg, not so many messages from Petrol car owners.
2or 3 Years ago a car magazine tested cars under realistic conditions and found some models performed better and some worse. Time we had a more realistic mpg test maybe?
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I used to be able to comfortably beat the official combined MPG when I spent most of my commute going up and down motorways, around 60 miles round trip spent between 50-70mph, rarely going faster and thinking ahead as much as possible to try and maintain a constant speed.
I averaged nearly 52mpg is a Vectra 1.9 CDTI doing this and 44mpg in an S80 D5 auto doing the same.
Now I work from home and spend little time on the motorway, I struggle to get around 35-37mpg, around the same as the official combined for my S80. If I don't do any longer journeys in the week this can drop as low as 28mpg, from a diesel!!! To be fair, that is about the same as the official quoted urban mpg for my car.
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It's quite easy - just preserve momentum. Use your eyes to observe the road/cars ahead and try to anticipate. Every time you brake, you're wasting energy.
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>>Every time you brake, you're wasting energy.
While this is true, I wonder why people tend to talk about braking more then over-running as a case of bad driving leading to high fuel consumption. It isn't as though overrun is in any way regenerative - you still lose the vehicle's kinetic energy to other forms of friction.
Having said that, braking excessively is probably indicative of a driving style which accelerates unecessarily, and that is where the fuel is really burnt.
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Having said that, braking excessively is probably indicative of a driving style which accelerates unecessarily, and that is where the fuel is really burnt.
Yup, sympathetic vs aggressive driving style. Obviously "flunky" prefers the latter.
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Accelerator pedal = uses fuel
Brake pedal = wastes fuel
There more you 'use' then the more there is to be 'wasted'
In normal driving on my commute I get around 35mpg from a 1999 A4 1.8. If I put in the effort I can quite easily get around 40mpg, if the traffic is light and I really go for it I can get up to 50mpg.
When I drive the supra its for fun, I have no idea what sort of mpg I get. Given that I do under 1000 miles per year in that car fuel costs are not of much concern
The only thing is I can't find the offical mpg figures for the A4 so I have no idea if I'm beating it or not!
Interesting to read the different responses, I guess some people have 'style' and some don't :)
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>>Brake pedal = wastes fuel
No more so than coasting to slow down.
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Yes, I agree.
That's why I tend to coast in nuetral when suitable to reduce the loss. It's a key technique for getting 50mpg.
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>>Yes, I agree.
>>That's why I tend to coast in nuetral when suitable to reduce the loss.
I think that you're still missing my point.
*However* you slow down, whether by brakes, by over-run, or simply by the friction from road load drag (i.e., rolling resistance, gradient load, and aerodynamic drag), you've still lost the kinetic energy, and it doesn't make a big difference to your fuel consumption how exactly you slow down.
The key is to drive in a way that minimises your need to slow or stop - by timing your arrival at junctions, traffic lights and roundabouts, for example.
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ok, get the point now. My point is the same just worded differently - once you have used the fuel you want to get th emost out of it - what I mean is that you don't want to stop unless you have to.
Yes, I agree - reading the road ahead is very important - as well as giving better mpg it also makes for much safer driving as well.
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>>ok, get the point now
Ah, sorry if I misunderstood.
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>>I wonder why people tend to talk about braking more thenover-running as a case of bad driving leading to high fuel consumption. It isn't as though overrun is in any way regenerative - you still lose the vehicle's kinetic energy to other forms of friction.
But the alternative is coasting, which us frowned upon, though I don't see why it should be at moderate speeds and with due care and attention. Driving gently the diesel CRV will average 40mpg (combined cycle official figure 42). With judicious coasting, keeping to speed limits, using the highest comfortable gear etc I have just done 550 miles before the light came on - 51.5 according to the computer, actually nearer 48.
Despite all the noise about fuel prices, I see little evidence that the majority of car drivers make any connection between their driving style and fuel costs - the tcommuter raffic on the A41 between Aylesbury and Hemel Hempstead still flashes by at 80-90, usually with lots of brake light flashes every time the speed of flow drops by a few mph.
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I really drive very gently these days with lots of anticipation, changing up a gear between 2-3000 rpm and as little braking as possible. However, the only way I can imagine that I could beat the official mpg figures on my Panda 4x4 would be to make my journeys with the engine switched off and the England Rugby 15 pushing me.
By the way, didn't you all like the cartoon on the front of the Telegraph today of the couple pulling their caravan cos they can't afford the fuel, with a huge queue behind them.
Maybe not so funny, could be that the horse will make its comeback.
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Dont forget that tyres can make quite an impact on the economy.
Certain Michellin's have a much lower rolling resistance, has do a certain Hankook range which will naturally result in better economy overall.
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brake pedal/engine braking/wind resistance/rolling resistance = wasted fuel
Over inflating the tyres will reduce resistance. I'm told that many taxi drivers do this. Not so sure if I would do this myself due to concerns over harsh ride and impact on tyre grip.
I read somewhere that some people are inflating their tyres up to around 50psi. I guess most tyres can handle that pressure but I would be more concerned about grip (or lack of).
Mind you, an over inflated tyre is probably a lot safer than an under inflated...
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Surely an underinflated tyre would grip more? I find just having it .1 bar over standard makes for a noticeably harsher ride on my Xsara.
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I was thinking safer because an under inflated tyre will have more grip but will also overheat and potentially blow out.
Which is more dangerous - less grip or a blow out?
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OK , any reason this turned into stars?
Basically it depends on the situation, and I'm sure the tyre manufactures would factor in users who only check their car once a year come the MOT thereby a bit underinflated over time.
Edited by smokescreen on 23/05/2008 at 18:18
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An underinflated tyre will adopt a profile, on contact with the road, where the outer edges of the tyre will provide more contact than the centre of the tyre.
Thus the contact is reduced, as is braking.
Similarly, overinflation will result in less contact of the outer edges of the tyre with the road, again reducing braking efficiency.
Car and tyre manufacturers don't do hours of tyre testing to establish optimum pressures just because they like a drive in the country, they do it to find the best compromise between economy, tyre wear and braking efficiency.
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>>again reducing braking efficiency.
Could you explain a this in a little more detail, Chris?
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It is very hard indeed to equal let alone surpass manufacturers' consumption figures in ordinary traffic or even in ideal rural conditions, except by adopting a special and rather tedious Mobil economy-run driving style.
It isn't difficult to get near them though driving sensibly in a good modern box. And that of course is good enough for me as well as most others. Lots of overrun and braking little and gently of course, but keep the thing rolling briskly along. Hesitancy is wasteful.
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It isn't difficult to get near them though driving sensibly in a good modern box. And that of course is good enough for me as well as most others. Lots of overrun and braking little and gently of course but keep the thing rolling briskly along. Hesitancy is wasteful.
Spot on, Lud!
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I'm not an engineer but as I see it, an underinflated tyre presents a concave area of contact with the road and an overinflated tyre a convex area of contact. Now this is a simplification, the concavity or convexity relates more to the relative pressure of contact with the road across the tyre. I know that my concept relies on a relatively stiff tyre sidewall and thus may be flawed.
I present these concepts on this site as it is how I see the physics of such situations. I'm quite happy to be shot down in flames by real and knowleagable engineers as that is the only way I will learn.
So NC, I await your valued opinion.
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>>I'm quite happy to be shot down in flames
Not at all! - I asked to try to understand exactly what you were getting at, hopefully to tailor my reply a little.
To all intents and purposes, the area of contact between a tyre and the road doesn't affect how much braking force can be applied - there's no real connection between contact area and braking efficiency as you phrased it.
Although rubber does have some odd behaviour, and as it conforms to the road surface, there is some area dependence.
As a first pass estimation, the area of contact is given by vertical load divided by the tyre pressure - the tyre behaves remarkably like a balloon, although you're quite right to point out that the sidewall stiffness is higher than the stiffness elsewhere - especially on a wide tyre.
For safety, what matters more than the absolute tyre pressure* is that the ratio of front tyre pressure to rear tyre pressure is kept on the safe side of a boundary. As you reduce tyre pressure, you reduce a proprty called cornering stiffness. Cornering stiffness relates how much cornering force you get per unit slip angle (slip angle is the difference between the direction of travel of that corner of the car, and the heading of the tyre itself).
If you reduce the rear cornering stiffness, (by reducing rear tyre pressure), or increase front cornering stiffness, you move the car's fundamental handling balance towards oversteer (this is not skidding behaviour, it's the behaviour of the car below the limits).
* The other way that tyre pressures can be made unsafe is that if you reduce them too far, the tyre deflects too much, and via hysteresis losses, the rubber overheats, delaminates, and you get a sudden blowout. This is real sudden catastrophic failure, with no warnings, as opposed to the handling changes which are quite obvious, and any reasonable driver would know something was wrong, and correct it, wheras the first you might know about under inflation is when the tyre goes bang.
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Thanx NC, I will now spend some time considering your explanation.
I think that you have introduced to me the practical concept that the balance of the car is very important in braking, especially in maintaining control and remaining in a straight line. To an experienced driver who always tries to maintain his car to a maximal degree this idea becomes second nature. However, I can see that imbalances in braking effect between wheels or axles can have a serious effect on braking efficiency.
Me Mam always told me I should have done engineering rather than Medicine.
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