fuel economy

hareng

Ultrasonic wrote: »

I do still firmly believe that it is very atypical for a mass-market road car to have better fuel economy at 80 mph than say 70 mph though (let alone 60 mph). Even for 6 speed cars.

Purely speaking of current 1800cc car on motorway 6 gears close ratio.
60mph 39mpg
70mph 35/36mpg
85mpg 27mpg
Thats taking the rough with the smooth ie losing momentum uphills and not booting it to retain that speed like cruise control would.

Previous car 2.2 petrol Vectra B 5 gears EGR blanked off etc.
60mph 48mpg
70 39mpg
85mph 35mpg

Biggest mod was fit a catch can. Vectra fuel economy increased average 2.5mpg, present car undecided as yet but between 2 to 4mpg.

forgotmyname

2004 Mondeo Estate 130bhp 6 speed.

Just towed my van 300+ miles, Trip shows 39mpg. I think its lying.

Soon find out, Due a fill tomorrow. So i will know how far out it was.

29 - 31mpg more like. I hope its not less

My brim to brim tests are mostly short journey's so those figures are probably no good to you.

Ideally what i need to do is brim in at a pump do the journey in one gear, Fill at the same pump and do the journey in the other gear.
Ive not done that.

My MPG shows between 26mpg and 70mpg on the spreadsheet.

forgotmyname

OK checked my outbound figures..
I filled up. Drove home less than 1 mile.
Next morning i drove to the caravan storage approx 10 miles.
Couple of short journeys at the other end, 3 journeys of less than a mile.

Next day 4 times into town and parked up.

Filled up on the way out. 39.70 litres. Is that really 39MPG ?

Or has someone slipped something into my tea?

And i never used 6th at all when towing. Left it in 5th.

greenman7

I have measured my mpg over the last 56,500 miles in my 2003 Citroen C3 1.4HDi. My average is 65.2 mpg using hypermiling techniques. My last 10 fill ups have averaged 69.9 mpg; I think I have now perfected the 'pulse and glide' technique to increase my mpg. I tend to use it a lot of the time even though passengers in my car are not aware of it. For example on a motorway I will accelerate to 65+mph (pulse) then take my foot off the accelerator and allow engine braking to say 57mph (glide), then accelerate again and engine brake again. Obviously it all depends on traffic conditions etc, I am always conscious of who is behind me and approaching traffic. For more tips go to hypermiler.co.uk and mpg comparisons on fuelly.com.

Strider590

greenman7 wrote: »

For example on a motorway I will accelerate to 65+mph (pulse) then take my foot off the accelerator and allow engine braking to say 57mph (glide), then accelerate again and engine brake again.

You should be shot......

Trebor16

forgotmyname wrote: »

The department of transport are probably the same people that think a loaf of bread costs £20.
And modern cars have 4 gears now and you should get into 4th ASAP.

6th gear is too high on some cars, I presume this is why the figures dont match what they have been telling us since the 70's.

My figures are not just random numbers plucked from this air. They are repeatable many times over.

A38, M6, M42 or the M69.

The Department of Transport may not know what a loaf of bread costs, but I wouldn't expect them to. But I suspect they know that when you double your speed it takes four times as much power to achieve the doubling of speed. Which is why more fuel is burned. The would also be aware that drag increases considerably above 70mph.

You say your figures are not random, but you haven't answered my question about what testing you have carried out to determine if your claims that your car uses less fuel at 80mph than at 70mphin sixth gear are indeed correct.

Trebor16

Ultrasonic wrote: »

Those figures probably assume a car with five forward gears, not six, which may be relevant? It would be interesting to know quite what they are based on but they must be some sort of approximation/average. As speed increases aerodynamic drag becomes increasingly dominent, and so I'd guess the relative fuel consumptions at different speeds are likely to vary with how aerodynamic the car is.

The number of gears is not of much relevance and it is the overall ratio of the highest gear that will have more of an impact. You could have a car with a 5 speed box where fifth is of a similar ratio to 6th in a car with a 6 speed box. Aerodynamics will also play a part but it doesn't matter ultimately how aerodynamic the car is as drag will still effect the fuel efficiency of the more slippery cars. The drag coefficient is not the only factor as the frontal area of the car will also affect things.

Ultrasonic wrote:

Having said all that, like you Trebor16 I still stuggle to believe forgotmyname's claims, but if he really does have brim to brim fuel economy data to confirm them, then I have to concede they are true (for his car). It's hard to say anything more without seeing the data. (Forgotmyname - would you be willing to share this? It would also be interesting to know what car you have.)

A brim to brim figure is not going to help us here. What we need is proper tests conducted at 70mph and 80mph, carried out in a variety of conditions, to prove or disprove the claim.

Ultrasonic wrote:

I do still firmly believe that it is very atypical for a mass-market road car to have better fuel economy at 80 mph than say 70 mph though (let alone 60 mph). Even for 6 speed cars.

I agree.

worried_jim

Strider590 wrote: »

You should be shot......

Spilling my tea laughing!

AlexisV

cyclonebri1 wrote: »

No they are not in answer to your question.

The fuel consumption figures are much more recent, plus the laws of aerodynamics have not changed.

What specific vehicle are they based on? Petrol/diesel, 5/6 gears, turbo or NA, hatchback or SUV, heavy or light vehicle, what capacity of engine?

Trebor16

AlexisV wrote: »

What specific vehicle are they based on? Petrol/diesel, 5/6 gears, turbo or NA, hatchback or SUV, heavy or light vehicle, what capacity of engine?

It doesn't matter what vehicle you drive, drag affects them all and the faster you go, the more power you need to overcome the drag and more fuel will be needed for this power.