MPG

[CyberCynth]

Sorry Mods, I know there's already a thread somewhere about MPG, but I can't find it.

Last time I posted about my towing MPG I think I was boasting 49, but accepting that I'd probably made a mistake in my calculations. After my last outing I rechecked it. Still thinking I must have made a mistake! Ok, someone else try the maths. Full tank at 26986 miles. 345 miles (260 of which towing) 35.60 litres of petrol to refill the tank. 345 divided by 35.60 x 4.55 = 44.09. Perhaps I'm making a mistake with the calculating formula

The advantage of the little Gobur folder is the lack of wind resistance. However, I still find it hard to believe my Skoda is taking so little account of the weight she's towing. (MTPLM 950kg, but I'd love to put her on a weighbridge fully laden) All I can think of is that the 1.2 turbo, which apparently provides as much power output as the previous Fabia 1.4 (no longer made, as the 1.2 does the same job)

Driving style? I try to remain within the legal limits but I do have to reign in the Skoda once she's got up some momentum. Driving solo, I'm perhaps not as sedate as a woman of advancing years ought to be.......says she, a former amateur rally driver.

 

[Boltmaker]

Hello CyberCynth,

To change litres to gallons you DIVIDE not multiply litres by 4.55.

 

[WoodlandsCamper]

Cynth is right because because she is dividing miles by litres to get miles/litre and then multiplying by litres/gallon. The litre units top and bottom of the calculation cancel out, leaving the answer in mpg.

 

[colin-yorkshire]

hi CyberCynth,
forget the maths for a moment and think positively. you got 345miles on 36 ltrs of fuel thats 9.58miles per ltr
now times this 9.58 by 4.55 [litres in a gallon] answer = 43.59 mpg
not as much as 44.09 but near enough and still very impressive.

 

[TheTravellingRooster]

Hi to all of you fuel consumption mathematicians.
I always use the one method of calculation and for the sake of the exercise - I am going to use the figures provided by CyberCynth.

Distance covered between full and refuelling = 345miles.
35.60 litres to refill.
35.6 divided by 4.5461 litres to the gallon = 7.83gallons.
345miles divided by 7.83 + 44.06mpg.

Just for the record I believe it was me that started an mpg debate/discussion/argument off some months back. I highlighted the inaccuracies of my 2005 905) Volvo V70 D5 SE Geartronic OBC.
I have recently carried out another brim to brim fuel check and the findings - yet again support what I had previously said and in real terms are far from encouraging in keeping a diesel powered car.
as an occasional tug.
The OBC was lying through the back-teeth when it showed an average mpg of 45mpg.
A brimmed fill-up and calculation showed 35.37mpg.
That is a massive 21% discrepancy.
I had actually covered 428miles with no towing duties and the brimmed fill-up took 55.00 litres.
Doing the same mileage in my old 1997 Volvo V70 T5 CD Auto I would regularly return 30mpg+ on petrol
When towing the Elddis Crusader SuperSirocco the T5 towing figure was 19mpg and the D5 towing figure was 22mpg - both at best returns.

 

[colin-yorkshire]

0.47 mpg difference impressive that is about the same as the amount of gas that goes on the floor when you take the nozzle out of the filler cap.
none of this of course is relevent to the actual running costs as it does not take into account the fuel price.
the best calculator is the price per mile, the actual cost will vary depending on price. and will give a larger differential
although to be honest I never bother it costs what it costs. I fill it, when its empty, I fill it again simple.
did the Cornwall trip a couple of weeks ago first one without the van could not believe the difference. [with the van] fill up at home, put some more in at Bristol, top up at Exeter, run round a bit fill up to come home, top up at Bristol again. then fill it when home.
[without the van] fill up at home go to Cornwall run round all week, fill up run round another week set off and get back with what's left in the tank. must be 50% saving on fuel and its dearer down there by 4pence a litre.
happy caravanning.

 

[CyberCynth]

Travelling Rooster; I shan't be buying one of the Volvo models you quoted any time soon. Ouch! Shall stick with my little Skoda, she's lovely!

So, concensus of opinion seems to back up my towing mpg? Colin, I agree with you too - it costs what it costs; if you want to go caravanning you have to put up with the expense! I do tend to feel though, that a check on the mpg figures are useful to keep an eye on engine function; if the mpg drops dramatically it could be a symptom of other problems developing. Or that's what I've been told in the past, anyway. P.S; glad I moved from Cornwall to Wiltshire! 4p a litre more for petrol??? My budget would struggle with a sting of that sort these days!

Thanks for your input guys!

 

[colin-yorkshire]

your welcome, from the figures you can confirm you are getting around 44mpg on a journey that includes mostly towing thats brilliant be happy with that, most I ever got with the meriva was 34ish while towing but it is one of those penalties you pay for towing with a smaller car. yes you gain solo but the differential while towing is greater .

 

[Raywood]

I did not realise the advantage of a folder was that big but towing a full size tourer is a bit like towing a barn door and wind resistance must be the main drag on fuel consumption.
My Mazda using a tank to tank filling on our trip down to Troutbeck Head and a bit of running round did manage about 36 mpg against the cars figure of 38 which seemed very reasonable to me.

 

[CyberCynth]

your welcome, from the figures you can confirm you are getting around 44mpg on a journey that includes mostly towing thats brilliant be happy with that, most I ever got with the meriva was 34ish while towing but it is one of those penalties you pay for towing with a smaller car. yes you gain solo but the differential while towing is greater .

Yes indeedy Colin, I'm a very happy bunny with those figures!

 

[JonnyG]

Hi to all of you fuel consumption mathematicians.
I always use the one method of calculation and for the sake of the exercise - I am going to use the figures provided by CyberCynth.

Distance covered between full and refuelling = 345miles.
35.60 litres to refill.
35.6 divided by 4.5461 litres to the gallon = 7.83gallons.
345miles divided by 7.83 + 44.06mpg.

Just for the record I believe it was me that started an mpg debate/discussion/argument off some months back. I highlighted the inaccuracies of my 2005 905) Volvo V70 D5 SE Geartronic OBC.
I have recently carried out another brim to brim fuel check and the findings - yet again support what I had previously said and in real terms are far from encouraging in keeping a diesel powered car.
as an occasional tug.
The OBC was lying through the back-teeth when it showed an average mpg of 45mpg.
A brimmed fill-up and calculation showed 35.37mpg.
That is a massive 21% discrepancy.
I had actually covered 428miles with no towing duties and the brimmed fill-up took 55.00 litres.
Doing the same mileage in my old 1997 Volvo V70 T5 CD Auto I would regularly return 30mpg+ on petrol
When towing the Elddis Crusader SuperSirocco the T5 towing figure was 19mpg and the D5 towing figure was 22mpg - both at best returns.

..

On board trips, lie both ways and i mean the same on board trip computer can and will under read and over read. it uses historic values from your driving style and journeys .also did you do the 428 miles in one journey? if so those figures are appalling, but if on the other hand it was five or 10 trips cold starts ect ect then 35 mpg isnt that bad. mind you the clues in the CO2/roadtax to how good a car is on mpg.....and a diesel will always be 15 to 20% better on mpg than a petrol in a simalar like for like. power weight cc...

 

[CyberCynth]

Ah, I wondered how long it would be before reality hit home. :S I returned yesterday from a few days away in the 'van; didn't go far, just fancied a trip out. That's what caravanning is all about in my mind; those lovely impromptu outings. I could have picked better weather for my mini-break, but, hey ho, can't win 'em all. Thought I would do another check on the fuel consumption, and didn't fare nearly so well as the previous two calculations. Only 36.5mpg this outing. Of the 266 miles I covered between fill-ups, 120 were towing, mostly motorway/dual carriageway. Mind you, that was in the teeth of a howling gale.......

 

[ProfJohnL]

How wound up we get with accuracy of MPG figures! Now I must qualify that little I know that some people will choose a car which they hope will provide good fuel consumption and that is a laudable, but the reliance on the figures produced by on board computers is almost always going to end in tears. They are not designed to be highly accurate measuring devices, and the way manufacturers are forced to produce and work out the official figures bears little resemblance to real life driving.

For reasons I have previously explained the readout is usually based on a running average, which may be over several hundred miles. Exactly how it does it will depend on each manufacturers designs. Even F1 cant get it right!!

It frankly isn't worth quoting results to tenths as even if the same driver were to repeat the same journey, its quite likely the results will be different on every run.

Rather than looking at the OBC as an absolute value, which can't be relied on implicitly, look at what happens to the trend, If its apparently improving then take solace in the fact you must be driving more economically.

As TR points out the best way of assessing your MPG is to brim to brim fill and calculate from the mileage between fills. However, even this method is not foolproof because you are still relying on the cars odometer, which in its self is not 100% accurate.

 

[JonnyG]

oh i don't know ,either a computer reading or a brim to brim reading is always far far better than the chap who quote it does 100 miles to a tenner or the bloke that says it does 40 mpg because he put 20 pound in and he knows exactly when he had used 20 pounds worth of fuel by looking at his fuel gauge! but seriously is it necessary for it to always become a case of pointing out the obvious! when somebody merely wants to know about their maths with regards working out their own MPG, instead we get a scientific lecture on how un perfect any measurement is outside a control scientific laboratory! news flash we live in an un perfect world! "wound up" wondering how wound up people must get to keep quoting how inaccurate everything is!

 

[CyberCynth]

Prof, if you had read earlier posts in this thread you would know that I haven't got an OBC in my Skoda, my figures are worked out mathematically, after topping up the tank following an outing with the caravan. I don't think I'm getting particularly wound up on the issue, just commenting wryly on the fact that the extraordinary mpg I'd achieved on earlier runs had, this time been reduced to a more realistic level!

 

[JonnyG]

"even F1 cannot get it right"..err i think you'll find F1 can get it right . unfortunately not even F1 can foresee the future,and a race is subject to ever differing circumstance's that effect both performance and indeed fuel usage not even precise laboratory testing can emulate varying race conditions or circumstance to give an absolute answer.
oh when was the last time you saw a Mercedes or red bull or Ferrari run out of fuel in a race before crossing the finishing line? so really as they have somewhere between 130 to 150 litres 100kg by weight on board and need 1 litre for testing after the race,they are able to control fuel usage to an accuracy of error of under 1% ...without any driver having to slow down to 50 mph.. now that's accurate...

 

[RogerL]

"even F1 cannot get it right"..err i think you'll find F1 can get it right . unfortunately not even F1 can foresee the future,and a race is subject to ever differing circumstance's that effect both performance and indeed fuel usage not even precise laboratory testing can emulate varying race conditions or circumstance to give an absolute answer.
oh when was the last time you saw a Mercedes or red bull or Ferrari run out of fuel in a race before crossing the finishing line? so really as they have somewhere between 130 to 150 litres 100kg by weight on board and need 1 litre for testing after the race,they are able to control fuel usage to an accuracy of error of under 1% ...without any driver having to slow down to 50 mph.. now that's accurate...

Red Bull have been disqualified for exceeding the permitted fuel usage rate, others have been disqualified for insufficient fuel for testing - all F1 cars are liable to be slowed down during the race to conserve fuel to ensure they don't run out - their ability to be so precise is a tribute to their radio-montoring of engine data.

 

[JonnyG]

"even F1 cannot get it right"..err i think you'll find F1 can get it right . unfortunately not even F1 can foresee the future,and a race is subject to ever differing circumstance's that effect both performance and indeed fuel usage not even precise laboratory testing can emulate varying race conditions or circumstance to give an absolute answer.
oh when was the last time you saw a Mercedes or red bull or Ferrari run out of fuel in a race before crossing the finishing line? so really as they have somewhere between 130 to 150 litres 100kg by weight on board and need 1 litre for testing after the race,they are able to control fuel usage to an accuracy of error of under 1% ...without any driver having to slow down to 50 mph.. now that's accurate...

Red Bull have been disqualified for exceeding the permitted fuel usage rate, others have been disqualified for insufficient fuel for testing - all F1 cars are liable to be slowed down during the race to conserve fuel to ensure they don't run out - their ability to be so precise is a tribute to their radio-montoring of engine data.

red bull [Richardo] were disqualified for red bull insisting on using their own fuel sensor after claiming the official F1 meter wasn't as accurate as theirs! they were informed in parc ferme of possible action since then red bull have complied and used the official metering system .sorry i don't know who this "others" is,who does he drive for? no matter he would be an exception in this season championship anyway.Also F1 cars for years are never ever fuelled up with enough fuel to complete a race flat out anyway,hence the numerous fuel maps they have.my point was/ is their fuel metering and the reading of is extremely accurate...