I read a post on here a while ago, which got me thinking. The interesting bit is this,
"1.4 GSI Getz is only returning 37mpg (several full tanks) which is the urban cycle consumption - despite a number of long outings"
Now, that seems pretty poor to me. My car gets more than this in stop-start traffic dispite my combined cycle being 1mpg less than this. It almost always gets over 40mpg, and on the motorway it can approach 60mpg (depending on conditions). If I got this car I would be very dissapointed because I wouldn't expect it to drink more fuel. I suspect the Getz would probably pay lower tax too, but in reality it is probably worse.
This week I saw an interesting thing in my local IAM newsletter. Apparently some Auto Express tests have show that the best-selling models do not live up to their claimed fuel consumption figures, with some using a third more. They said that the official figures should be taken with a pinch of salt. This could make the difference between a car being very green and a car being very environmentally unfriendly. If this is true, then how do we work out the fuel consumption of vehicles? Should we test drive all models for a few hundred miles to get consumption figures? Is modern trickery (stop-start nonsense, and hybrid) badly distorting these figures? Do these tests need updating? Maybe test the emissions at idle, emmissions when cruising at different speeds and then when accelerating?
I also wonder how the performance figures compare. I've driven the Aygo and Panda, which had similar performance figures, but they felt slow, even compared to my car which takes almost 5s long to hit 60mph. I then drove a 1.2 Corsa which was the complete opposite, it felt really fast, dispite less than a 2s difference in 0-60 times.
When we're looking for cars to test drive how do we get a short list, should we just ignore performance/economy figures and test drive everything?
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'When we're looking for cars to test drive how do we get a short list, should we just ignore performance/economy figures and test drive everything?'...
In my opinion....yes! I would never buy any new car without first having a test .That is the only sure way of assuring yourself that you are entirely satisfied with the performance and that all other aspects are completely appropriate to your personal requirements before parting with your 'hard earned'.
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OK, you've let us know you are an advanced driver; so, what is your car?
Numbers don't really mean very much do they? What does it matter if one car does 1.5mpg more than another when you are pouring money into the bank or the chancellor's pocket every day anyway, not to mention the depreciation factor...
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When buying our family cars we've always test driven them, the latest acquisition being an example Mrs P's GTi feels very much quicker when we got it :-). Does the comment also mean we need to take a stop watch and do a brim test on a test drive ?
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No need for stop watch or anything so scientific. Just stop buying cars based on emissions and economy.
Let's all go back to buying cars like we did when we were younger..... based on the following criteria:
1. Will it help you pull?
2. If it succeeds at "1" will the seats recline enough?
3. Can it leave rubber behind at the lights?
4. Has it got a big stripe?
Then again, it was choosing cars by this criteria that sold the old Allegro 1850........
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OK you've let us know you are an advanced driver; so what is your car?
Fiat Seicento 899cc.
Numbers don't really mean very much do they? What does it matter if one car does 1.5mpg more than another when you are pouring money into the bank or the chancellor's pocket every day anyway not to mention the depreciation factor...
Ah, but that's not the case, the if the figures are out by a third then the figures could be out by over 20mpg, just on the combined cycle (if that's what Auto express were going on). So a car that is 1.5mpg better may actually be more than 18mpg worse, which is a LOT! If you spend £1000/year on fuel you could be looking at more than £300 extra, not to mention the environmental impact.
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Ah yes, you should definately test driven them, but I narrow our choices down first, and the performance/economy figures are an important factor. The importance of these figures will depend on what the car's for and who the buyer is.
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Apparently some Auto Express tests have show that the best-selling models do not live up to their >> claimed fuel consumption figures with some using a third more. They said that the official figures should be taken with a pinch of salt.
The issue here is that *some* cars don't get anywhere near their laboratory tested fuel economy, yet other cars apparently do. Why is that?
We know that manufactuers do things like putting thin oil in the ebgines, or tweaking the ECU for economy, but surely they all do the same things, so the comparison should be valid.
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Oh, I didn't reallise that they tweak the ECU etc., that makes the tests almost useless! I suspect that some cars a designed to be economical for the consumption tests, eg. lowest consumption will be at the speeds the tests are done at.
One thing that gets good performance figures is making sure that you can get to 60mph in 2nd gear, which eleminated a gear change, saving a considerable amount of time. I think they did this on the Saxos.
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All you are seeing is that once a test is well known, some cars will be engineered to do well in it. The same, of course, is true for NCAP tests. Some cars will just simply perform well, and others will only perform well under the test conditions, and some (like the Chinese example) simply perform badly all over.
It's a similar thing to NHS targets. There's a target that says that you will be seen by a nurse within X minutes of going to A and E. The smart hospital managers simply replaced the receptionist with a nurse - bingo!, everyone is seen by a nurse within seconds of entering the A and E, even if they then need to sit around for a few hours waiting for a nurse who will actually *do* something for them!
However, we do need tests to help us decide between cars - and these test must be standardised, to enable a fair comparison. I'm sure the tests are way more accurate than most* people's attempts to measure their own fuel consumption figures.
Number_Cruncher
* with the obvious exception of the Focus driving mollusc!
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Performance figures are misleading too. Not many people are going to achieve the optimum 0-60 time for their car by abusing the transmission, front suspension (in most cases) and tyres.
Times for 30-50 in, say, third gear and 50-70 in fourth are more meaningful to the road driver.
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Many cars come with a choice of engine sizes. A bigger engine should at least be similar to, if not better, a smaller engine's fuel consumption in the same body.
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What\'s for you won\'t pass you by
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snipquote -PU
Uh? That's the wrong way isn't? A bigger engine should drink more fuel than a smaller on in the same body.
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Snipped - PU
Not necessarily P3. If the performance is used to the full perhaps, but the point is that a bigger engine doesn't have to be worked so hard and the car can have higher gearing. I seem to remember that Renault made a super-economical Renault 5 that had a much bigger engine than its predecessors and higher gearing, as well as a couple of years of technical progress in engine design....
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I used to have a four-speed 1.3 Jetta and eventually changed it for a bit more overtaking oomph to a five-speed 1.6TX - the latter returned up to approximately 50 per cent better fuel consumption overall. Apart from the extra 300cc, the only noticeable changes were central locking and the bigger plastic bumpers.
You particularly noticed the difference, obviously, with passengers aboard.
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What\'s for you won\'t pass you by
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most cars have an optimum engine to go for, if you want an extreme example i can think of a montego with a 1300 ohv or a 2.0 litre ohc,the 1600 was the best engine for this car for pootling around but im sure someone will be along in a minute and say the refined diesel was the best one ;-)
My primera is much more fuel efficient in 2.0 litre rather than the 1600
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>>the refined diesel was the best one ;-)>>
You mean the Perkins lump?
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What\'s for you won\'t pass you by
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You mean the Perkins lump?
no the o series with a different head ;-0
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Manufacturers neither "tweak the ECU" or "put thin oil" in the engine. Fuel,emission and engine performance tests;these tests are all officially observed by Government inspectors from one of the EU countries and the certificates they issue are valid for all EU countries.Their official stamp goes on the report as the representative of their government.Emission and fuel tests are carried out to a drive cycle which has periods of idle,acceleration,cruise and deceleration which,I agree,does not represent average driving but does allow for comparison betwwen makes/cars.The road load(used for setting the test equipment)is also observed by a certifying authority.
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Manufacturers neither "tweak the ECU" or "put thin oil" in the engine.
I meant that the ECU's program is designed to give the best emission figures (it's from those that the fuel consumption is calculated - fuel consumption itself isn't measured). 0W30 grade oils are used for better economy.
However I would say that I don't for one moment believe that the engine submitted for test is some random engine pulled off the production line.
but does allow for comparison betwwen makes/cars.
It doesn't if some models don't get anywhere near their rated fuel consumption, yet others have no problem meeting or even exceeding the quoted figures.
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The engines certainly won't be off the production line;these tests will have been completed months before a car/engine goes into production.However,as part of ongoing quality control programmes,both engines and vehicles will be checked and,also, the certifying authorities can, and do,carry out random checks on production vehicles/engines;these procedures are written into the relevant regulations/directives.As to fuel consumption being calculated from emission figures,partly right-it is certainly calculated but the emission tests are carried out from a cold start whilst fuel tests are run from a hot start.
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Some years ago one of the motoring magazines carried out tests on four makes of car that were available with different size engines.They drove these vehicles on four different test routes ranging from 100% city to 100% motorway;the only time the smaller engines were more economical was the 100% city;as soon as the average speeds increased,the bigger engines were better.
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The only figure I take into consideration is power/weight ratio. I wouldn't consider anything with less than 160bhp per ton.
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Abracadabra - PU
Your wife has a Golf GTi (Mk5?) which has a p/wt ratio of 147bhp per tonne (or 149.82bhp per ton) unladen weight 1336kgs, BHP 197.
It's safe to say you had no input in this ?
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Abracadabra - PU Your wife has a Golf GTi (Mk5?) which has a p/wt ratio of 147bhp per tonne (or 149.82bhp per ton) unladen weight 1336kgs BHP 197. It's safe to say you had no input in this ?
I did wonder if someone would mention that but thought that nobody would be quite so up their own posterior. Anyway I have the answer to hand which I didn't bother mentioning before.
I chose her car, she chooses our kitchen equipment- hehe!
Our Golf has been rolling roaded at 261bhp.
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:) Oh ! it's dark up here....
It's like me saying I would never buy a car with anything less than 17" wheels, then buying a car with 14" wheels knowing that with a bit of metal chopping around the wheel arches and a few hundred quid in my back pocket I could go to Halfords and stick 17" wheels on pretty much any car.
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:) Oh ! it's dark up here....
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Our car was already remapped when we purchased it.
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In that case pretty much any car can be made to hit your 160bhp/ton criteria then, even a twenty year old Mk1 Fiat Uno Turbo with mild chip tune to 136bhp, kerb weight 780kgs p/wt 174 or 177 (tonne or ton) if you can find anyone who can still programme a ZX81 :)
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In that case pretty much any car can be made to hit your 160bhp/ton criteria then
That's total nonsense and you know it. There are any number of examples that disprove it as you are well aware.
In any case I think 200bhp per/ton is more like it the 160bhp figure is that I'd consider adequate for a car to do the supermarket run in..............
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I am sure that someone can enlighten us to how the test actually works. As far as I am aware, the car is put on a rolling road and hooked up to computers and that is how they work things out.
I am sure that it would make much more sense to use somewhere/one like MIRA to do the tests on actual roads rather than a rolling road.
I do think that MPG figures are hugely important for a lot of people and their decision whether to buy or not, so manufacturers theoretical figures that are nigh on impossible to replicate out side of a laboratory must surely be verging on false selling/advertising. I also remember talking to my local dealer who said that certain cars perform better/worse than other identical ones.
Unless you are buying a brand new model, it is possible to garner so much information about mpg from various forums on the www, so it should be easy to verify or not the manufacturers' claims.
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>>I am sure that it would make much more sense to use somewhere/one like MIRA to do the tests on actual roads rather than a rolling road.
I am quite sure that the opposite is in fact true. To use a real track, how would you collect the tailpipe emissions?, how would you deal with the varying weather conditions?, how would you accomodate all the cars which need to be tested at one track (there aren't any *identical* tracks), how would you make sure the cars followed identical paths round the track? How would you control the friction levels between track and tyre? How would you choose the test driver to use?
In a lab, with a rolling road, you can control the conditions of the test - this is vital to enable any sort of meaningful comparison between cars. In a lab, you can use either a robot to directly control a car, or have a computer instruct a test driver to reach a particular speed - this could be quite difficult in the coditions of a test track (although handling robots which put in known steering inputs have existed for some time)
Number_Cruncher
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I still think all this talk about how to establish exactly how much fuel a car uses is to miss the point. It seems - to me anyway - only an issue because people notice what they have to pay straight out of their pockets.
But a few hundred pounds a year for fuel can pale into insignificance beside the amount of interest paid every month on a car loan standing order or wages removed in company car tax, let alone the hidden cost of depreciation.
I did a rough calculation the other day that showed an Aston Martin DB9 is likely to cost at least 55 pounds a day in lost value.
But if you've never actually seen the cash you don't miss it so much, do you?
Maybe that's why I know so many people who own impressively new up-market cars that have the low fuel warning light on most of the time.
So, yes, what I am trying to say is that owning and running cars is indeed just a numbers game.
Better to buy what appeals to you and stop worrying about it.
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I think the tests have to be done in lab, but there ought to be some realworld test available as well, although clearly there would have to be a fairly wide tolerance.
Look at the fuss there's been about Honda Accord CTDi - Honda produced a car with great CO2 figures so it made a very attractive company car choice as the tax was low. It should have been capable of 50MPG but many owners struggle to get 40, which makes a heck of a difference to running costs.
My daughters 1.2 VW engined Seat Ibiza is way off the combined figure - it should do 47.9 but I can't get it over 40, yet our Jazz and my Mercedes easily beat their combined figures.
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It is SWMBO Getz in question. Definitely thought we'd have got closer to 50mpg.
Otherwise running and performing admirably.
My Passat 100 ps PD also has dissapointing mpg. Averaging 45mpg in the warmer weather but normally only 42mpg overall. Spends a lot of time indicating 30s and even teens on computer even under gentle acceleration or slight gradients. Had it from new and now celebtrated 98k at weekend.
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..... although handling robots which put in known steering inputs have existed for some time ......
Mostly driving round the M25 etc....... :-)
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