Fuel Economy Reporting Thread

cecilia_aldridge

I may have missed it, but can anyone tell me the best speed to drive for economy

Crabman

cecilia_aldridge wrote: »

I may have missed it, but can anyone tell me the best speed to drive for economy

Welcome to MSE :beer: It's usually around the 50-55mph mark though this increases dependent on the engine size. The larger the engine, the higher the most economical speed will be.

PrincessG_2

shimmyshack wrote: »

"wind resistance goes as square of speed"
anyone who needs confirmation of this well known rule, need only look as far as
http://en.wikipedia.org/wiki/Drag_(physics)
(see the secton on drag at high velocity)
"Assuming a constant drag coefficient, drag will vary as the square of velocity."

Not many cars I know of change shape as they increase speed, consequently they do indeed have a constant drag coefficient.

A graph of force vs velocity that increases exponentially - now /that's/ rubbish

Yes, the wind resistance increases with speed - BUT drag is not the only force the car has to overcome. It also has friction, engine inefficiency, rolling resistance and such like. Drag is just a small part and doesn't have a huge effect on things like cars (lorries maybe).

Sorry to go all techie but I didn't spend 4 years at yoo-nee-ver-city for nowt

kaya

all cars built after 1997 have an ecu, they will operate from a predetermined fuel map when accelerating hard ,and run in closed loop mode(using the air/lambda sensors to determine fuel use) when cruising, when you put your foot down your adding as much fuel and air as your system will allow, in cruising or closed loop your engine can work out the fueling/economy and adjust accordingly

Paul1_2

Since I bought a car with a computer that works out you MPG it's does have an effect on your driving, sticking to 70 will achieve over 64 mpg and be happy in the knowledge that the Govs loosing money! Just think of the impact of cars showing MPG and cost per mile, would you really want to burn an extra £5 to get to the next set of lights?

Paul1

The_moose

I have a Skoda Fabia 1.9 TDI (diesel) and it is excellent on fuel consumption. On a journey where I drive faster I get about 52 MPG, drive sensibally and get 65mpg, and being really careful I can get 70+mpg. I did a 300 mile round trip on the motorways and got 74mpg!

And the best bit is that because it is low emissions it is only £115 per year road tax.:D

Iluvorkney

plane_boy2000 wrote: »

You also need to remember that a/c systems are more efficient now than they use dto be, and in the summer the effect of opening the window changes the co efficient of the car so you burn more fuel. In a lot of cases opening the window has the same effect as having the air con on.

Nothing personal, but if opening your window is as good as having the a/c on, you want to get it seen to

smurf_2

I think he meant in terms of fuel economy rather than cooling ability.

AP

Myron wrote: »

Okay... I know I'm cheating by owning a Toyota Prius but recently, and with the optimal style driving I manage to get well over 20 minutes of over 100mpg. For my commute to the office and back 20 minutes is about 12 miles.

If I mostly use cruise control then I can't achieve over 100mpg for such a long duration because cruise maintains a set speed and in a urban environment this is not always a desired action.

For any vehicle a predictive style of diving needs to be adopted and not a reactive and/or lazy style of driving.

Would you be able to tell me what your 'optimal syle driving' is to get over 100 mpg on a Toyota Prius?

I've got a Toyota Prius T Spirit and the best I can get is 64.3 mpg driving southbound on the M5 at constant 60 mph under cruise control.

DontDoDebtKids

I've been driving carefully since filling up last week and really found that this comment is true, having monitored my trip computer carefully:

ajuniper wrote: »

I find that being gentle on the accelerator is much more important when the engine is cold - having to stop at a few junctions early in the journey can make a surprising difference on the overall economy of a journey.

I tracked my spend for three weeks prior to the last fill up and was getting about 33mpg average in my 1.8 Petrol Octavia. I'm now up to a week since my fill up (normally I would have to fill up by now) and I've got just under half a tank to go, and I've managed just under 50mpg per trip according to my trip computer.

I await the average mpg for this week's fill up, hopefully later this week (is friday too much to hope for?)

Oh, and I've cleared out all the rubbish in my boot...can anyone beat three (heavy) bags of grit for the garden just lying in your boot?