Downside to cheaper petrol.

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beardy
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Re: Downside to cheaper petrol.

Post by beardy »

al_yrpal wrote:
Mick F wrote:Yes, the Fiat500 is a Twinair 2cyl 85bhp and goes like a rocket. The CO2 is 99gms per Km, and that puts it into the zero VED category. We can get 60mpg out of it on a run on the motorway, but locally it returns just less than 40mpg.

The 1.6 16v Clio OTOH has 170gms per Km. It can give 55mpg on a motorway, but locally it's more like 35mpg ........... ie not a lot different economy to the Fiat500. It's the CO2 that's the difference.


Blimey! I had noticed that those Fiats streak along but those figures make it less economical than my Mitsu ASX Cat 5 diesel 1.8 4wd. I have never got 60 mpg. More like 45 mpg whatever.

Al


Probably a reflection on driving styles. How you feel about using the brakes and throttle, how long your journeys are and the type of terrain you drive on. If I was to take the lanes instead of the A and B roads my mpg would plummet, a big heavy diesel likes to cruise on straightish, flat roads with no interruptions.
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Mick F
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Re: Downside to cheaper petrol.

Post by Mick F »

Yes. Very very true indeed.

Try driving round here.
If I reset the trip meter (engine warm!) at home and drive up the road to the next village a couple of miles away, I'll have done 15mpg.
Reset, then turn round and come back, and the mpg figure is off the scale at 99.9mpg but the brakes are on most of the way. :lol:

Try cycling round here!
Either in bottom gear struggling, puffing and panting up the hills ............ or 40mph flying back down.

It all takes its toll. Fuel, brakes, tyres. Get on a motorway and take your time, and there's hardly any effort.

70mph in the 500 will get 60mpg if you don't keep slowing and flooring it getting through busy motorway traffic. The car is good for 100mph+.
The Clio OTOH, will do about 40mpg at 70mph, but if I slow to 65mph or slightly less, I can get 50mpg out of it. Take it over the limit, and the fuel consumption plummets. By all accounts, it'll do 120mph.
Mick F. Cornwall
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al_yrpal
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Re: Downside to cheaper petrol.

Post by al_yrpal »

beardy wrote:
Probably a reflection on driving styles. How you feel about using the brakes and throttle, how long your journeys are and the type of terrain you drive on. If I was to take the lanes instead of the A and B roads my mpg would plummet, a big heavy diesel likes to cruise on straightish, flat roads with no interruptions.


No motorways or dual carriageways around here, plenty of hills and narrow lanes although not as hilly as Devon and Cornwall. The Mitsu will do 45 mpg all the time as long as you stay under 75, if you floor it and average higher than 75 it returns about 38mpg. It has quite an advanced engine with variable valve timing and very low emissions. In four years I have only done 18000 miles so I will be keeping it for a while. I am surprised tbe Fiat mpg varies so much, plenty of very short journeys up and down steep hills on the choke to the pub I guess? :lol:

Fitted a new battery to my wifes car this morning, what a struggle! Modern motor mechanics need to be contortionists with mega toolkits.

Al
Reuse, recycle, thus do your bit to save the planet.... Get stuff at auctions, Dump, Charity Shops, Facebook Marketplace, Ebay, Car Boots. Choose an Old House, and a Banger ..... And cycle as often as you can......
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Mick F
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Re: Downside to cheaper petrol.

Post by Mick F »

The main problem with fuel efficiency is aerodynamics. If you have a nice slippery car with a low drag coefficient, and an economical engine, you're quids in.

Drag coefficient of a Fiat 500 isn't good. 0.33cd I think.
This is because of its cutesy looks. Look is everything to the markets.

I bought the 500 for it's looks and the very interesting 2cyl engine - and the fact that it's zero VED - not for its outright economy.
Mind you, it's classed as a "city car" and in that environment, it's very good indeed.
Mick F. Cornwall
iviehoff
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Re: Downside to cheaper petrol.

Post by iviehoff »

Mick F wrote:
Samuel D wrote:CO2 is directly proportional to the weight of fuel burned ...........
There's much more to it than that perhaps?

Surely, CO2 is a by-product of burning fuel in a particular engine, not directly proportional per litre burned. Differently designed engines will produce less CO2 than others. Yes?

No. It is a matter of very basic chemistry as taught at GSCE. Each atom of carbon in the fuel is converted to CO2 when the engine combusts it. What else do you propose happens to it? Clearly a little bit of uncombusted or partially combusted fuel can sometimes be seen coming out the exhaust pipe, for example as soot, but that is tiny unless the engine is very faulty. And there is a tiny amount of carbon monoxide, 'cos people can poison themselves with exhaust fumes in an enclosed space, but it only takes very tiny amounts to poison you. So it doesn't quite all convert to CO2, but I would say that something like 99.9% is a reasonable estimate of the conversion rate even in a Model T Ford. So basically the CO2 is precisely related to the quantity of fuel consumed.

The kind of fuel makes a difference. CO2 per litre is 5-10% higher for diesel than petrol, depending upon the precise composition of the fuels, but that's because diesel has more energy per litre ("higher energy density") than petrol. In general, diesel vehicles put out less CO2 per km, because diesel engines are inherently more efficient, even after correcting for the higher energy density of the fuel. That's why we British diesel users are content to pay more per litre for the stuff. The increased NOx output of diesel engines is only a problem in areas of high pollution, it's really irrelevant everywhere else. What we really need in our cars is something like that Volkswagen software, but which changes the engine tune according to our location, prioritising pollution when in dense conurbations and the like, and prioritising efficiency everywhere else.
Last edited by iviehoff on 29 Jan 2016, 3:29pm, edited 1 time in total.
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Mick F
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Re: Downside to cheaper petrol.

Post by Mick F »

Thanks for that. A day isn't complete until you learn something! :D

Strange that some economical cars produce more CO2.

Our Clio is rated at 170g per Km. So that must be directly proportional to the tested fuel consumption.
Our 500 is rated at 99g per Km.

Therefore, there must be a table or an equation to work this out?
Why have CO2 per Km as a figure when they could just use MPG?

I reckon (or at least I did reckon) that MPG and CO2 weren't directly related. But as they are, there must be a conversion figure.
Mick F. Cornwall
iviehoff
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Re: Downside to cheaper petrol.

Post by iviehoff »

Mick F wrote:Thanks for that. A day isn't complete until you learn something! :D

Strange that some economical cars produce more CO2.

Our Clio is rated at 170g per Km. So that must be directly proportional to the tested fuel consumption.
Our 500 is rated at 99g per Km.

Therefore, there must be a table or an equation to work this out?
Why have CO2 per Km as a figure when they could just use MPG?

I reckon (or at least I did reckon) that MPG and CO2 weren't directly related. But as they are, there must be a conversion figure.

There is. For a petrol car take 6760 and divide that by the mpg. For diesel use 7440. Clearly as mpg goes up, CO2 per km goes down. See
https://www.eta.co.uk/2010/02/22/calcul ... m-its-mpg/
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Mick F
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Re: Downside to cheaper petrol.

Post by Mick F »

OK.
Simple bit of transformation, it means that 6760 divided by the CO2 figure equals the MPG

99g per Km for our 500 twinair works out as 68mpg. :lol: :lol: :lol: :lol: :lol: :lol: :lol:
No way is this true.

170g per Km for our Clio works out as 40mpg.
Now that seems correct to me as we often get that figure or even exceed it.

Therefore Fiat are cooking the books. :lol:
No way on God's Earth that we can get 68mpg diving it exactly the same in the Clio that returns 40mpg.
Mick F. Cornwall
iviehoff
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Re: Downside to cheaper petrol.

Post by iviehoff »

Mick F wrote:99g per Km for our 500 twinair works out as 68mpg. No way is this true.
170g per Km for our Clio works out as 40mpg. Now that seems correct to me as we often get that figure or even exceed it.
Therefore Fiat are cooking the books. :lol:
No way on God's Earth that we can get 68mpg diving it exactly the same in the Clio that returns 40mpg.

The rules on the way in which fuel consumption, and pollutant emission, is measured in the EU in effect invite people to measure them in a way that will not in practice be achieved on the road. This is well known, including in government, it was a government official working on vehicle emissions that I first learned it from. However there are legal practices and illegal practices. Also different models vary quite substantially in how far they are from realistic road measures, I think up to 30% difference has been noted in some recent realism checks. There was no way the car industry could achieve the EU targets they were given without, shall we say, a bit of latitude in the measurement methods, so there was a bit of latitude in the measurement methods. On the other hand in the USA they have rules that the measurements - although done in a lab - have to be "realistic" and they reserve the right to do on the road tests to check their realism, which is why Vokswagen was so bang to rights in the US. It is now recognised in the EU that there has to be migration to realistic measurement methods. But people have to be given time to devise better engines. There is also the problem that present day engines can be tuned to produce a lot less NOx, but generally at the cost of much worse fuel consumption. I don't really think that is acceptable.

68mpg is entirely achievable in modern small cars, and in a car that is perfectly pleasant to have and drive. I once hired a car when on holiday that did give me about 70mpg. And I was driving it over the hills. It was a small turbo diesel, iirc a Daihatsu. It was a small car, but it was a nice car, and I had the power to get up all those hills. I was astonished. That was about 7 years ago. More recently I hired a Volkswagen Polo with a turbodiesel for driving around a hilly area, and it was horrible to drive, and nowhere near as efficient as the Daihatsu. I was disappointed.
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al_yrpal
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Re: Downside to cheaper petrol.

Post by al_yrpal »

One has to remember that modern cars have power sappers - catylitic converters and DRLs on diesels.

Al
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Mick F
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Re: Downside to cheaper petrol.

Post by Mick F »

iviehoff wrote: ..........68mpg is entirely achievable in modern small cars .............
I wasn't suggesting that it wasn't.

I was saying that there is no way on God's Earth that our Fiat500TA could achieve 68mpg .................. unless it was driven on a flat motorway at a constant 50mph. It could get to 70odd mpg like that, but on real normal roads, even driven gently, it's impossible.
Mick F. Cornwall
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