£80 to fill up!

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[TW]Fox;19990621 said:
3mpg from not filling the tank?

my car would be roughly 25kg lighter with out the extra weight of 30 litres of petrol, wales is'nt the most level place to live and yes our hills/mountains do go down and not just up :D

Im just going by past experience of driving my car for year and half+
 
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my car would be roughly 25kg lighter with out the extra weight of 30 litres of petrol, wales is'nt the most level place to live and yes our hills/mountains do go down and not just up :D

Im just going by past experience of driving my car for year and half+


Are you saying that from experience, you save a significant amount of money through not filling the tank fully? I'd like to know how you've calculated this and your results.
 
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Are you saying that from experience, you save a significant amount of money through not filling the tank fully?

As part of my 'pre phd' work I have been reading the odd thesis or two on sustainability, papers, books etc. The last few days I have read all of the 2011 'Automotive Engineer' and it is all about new powertrains, aerodynamics etc just to save a few co2 and a few mpg.
I have no idea of the circumstances in which the co2 ratings are done, but if they are on a full tank, then making the fuel tank much smaller would save a few co2.
Automotive engineers really are doing everything they can to incorporate new things into a new car, such as more airbags, better safety, more gadgets whilst making the car lighter than the previous generation.
It seems the entire focus of the auto industry is focussed upon co2 (which afaik is co2 equivalent, as Nox etc are worse than Co2 and are accounted for in the co2 value).

Luckily for the customer, the best way of reducing what comes out the exhaust pipe is to reduce fuel consumption, via more efficient engines, better aerodynamics and lighter cars :).
 
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Soldato
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Do cars have no mass on a rolling road?!

Of course they do but they don't have to accelerate it because it stays in exactly the same spot whilst the wheels spin on the rollers.

Sure there might be a little bit of extra friction on the rollers but nothing massive, nothing that would even register a difference in economy or emissions figures.

I think the rollers are set to provide a certain resistance based on standard kerb weight and air resistance figures to simulate real world conditions. How accurate that process is I have no idea.
 
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I tend to find similar but that's because i consciously think 'wahey, got a full tank' *stamp on pedal* :p

Me too. Full tank and I'm Jensen Button. Nearing the red and it's like someone's glued an egg shell to my accelerator pedal and they're holding a gun to my head, the trigger to be pulled if the egg shell should shatter.

I hate visiting petrol stations. I'll always brim it. Always. But I love driving, so if I have to fill up, I have to fill up. And no, it won't make 3mpg of difference in the average car having the tank half full or full or whatever. That's utter bunkum.


Oh, and I always brim the MX5's tank too. And no I don't notice a difference in performance or handling. It's just handy, because it means I can go a month+ without filling up if I don't use it a great deal :)
 
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I average around 0mpg commuting - work being 5 minutes away by bicycle is a dream!!

Volvo V40 takes ~£80 to fill up, but that lasts me a month and a half, Discovery is more than £100 a tank these days, but it's only used for playing off-road at the weekends...
 
Soldato
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Of course they do but they don't have to accelerate it because it stays in exactly the same spot whilst the wheels spin on the rollers.

Sure there might be a little bit of extra friction on the rollers but nothing massive, nothing that would even register a difference in economy or emissions figures.

I think the rollers are set to provide a certain resistance based on standard kerb weight and air resistance figures to simulate real world conditions. How accurate that process is I have no idea.

They do a coast down test to get a measure of the cars rolling resistance. The resistance of the rolling road is then set to mimic this.
 

Bri

Bri

Soldato
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I tend to put £20-30 in at a time. If I fill the tank, I tend to do more unnecessary drives out at the weekend.

[TW]Fox;19989271 said:
This sort of comment just boggles my mind.

If I know I have a full tank I'll make outlandish suggestions to the wife to go for a drive to Durham/Newcastle/the Metrocentre when we have no real reason to go. Invariably she agrees so not only do I use petrol that I didn't need to, we buy stuff that we didn't need as well :)
 
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Well I do really wacko things like brim my tank every time and use my brain to decide not to drive somewhere if I don't want to go or to calculate that I don't save money by visiting the petrol station 6 times a week or to grasp the incredible concept that £90 once a month is the same as £10 9 times a month.

But it seems I am in the minority.
 
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[TW]Fox;19994535 said:
Well I do really wacko things like brim my tank every time and use my brain to decide not to drive somewhere if I don't want to go or to calculate that I don't save money by visiting the petrol station 6 times a week or to grasp the incredible concept that £90 once a month is the same as £10 9 times a month.

But it seems I am in the minority.
HERESY

burning.jpg
 
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Isn't filling up with 10/20 at a time the thing you do when you borrow your parents' car when you first pass your test and don't have a job? It's certainly not something that seems to have any benefit once you're a fully productive member of society.
 
Soldato
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Of course they do but they don't have to accelerate it because it stays in exactly the same spot whilst the wheels spin on the rollers.

Sure there might be a little bit of extra friction on the rollers but nothing massive, nothing that would even register a difference in economy or emissions figures.
I'm no physicist but my brain tells me that there are two key resistances to the motion of a car - air resistance and friction. Friction is the result of the weight of the car multiplied by the coeffecient of friction between the surface of the tyres and the 'road'. Friction is what makes heavier cars accelerator more slowly, so that "little bit of extra friction" is all that there is on the road; I don't think there are any other (significant) forces involved? If the rollers replicate the friction of a road surface weight is accounted for almost completely.
 
Soldato
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My car is a Hybrid so if I had 25 litres of fuel in the car rather than 55 it would make a noticeable difference to my MPG say 3+mpg

30*0.711=21.33 so your saving 21.3kg by not filling the tank, that's less than 1.5% of the weight of a Prius with driver (don't know what hybrid you have) assuming the 1.5% weight saving translates directly to a 1.5% mpg increase (it won't) you would get an absolute max of 1mpg out of that (assuming the most economical driving possible to meet the cars advertised max mpg), what your describing is called a placebo effect.

Also another reason why its best to fill the tank is that the fuel pump depends on the fuel to keep it cool, driving around with low fuel can cause the electric fuel pump to die sooner and the cost of a new pump could buy a lot of petrol.
 
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