How much do you save by driving with the windows open?

Mr_Toad

Lum wrote: »

This thread isn't about windows down vs aircon, something that was covered pretty well on Mythbusters a few years back.

This is about windows down vs making your child suffer and then puke all over the back seats.

Windows down it is.

Quite.

What sort of parent is prepared to make his children suffer just to save a few pennies.

s_b

Strider590 wrote: »

This......


Open a window and pretty much all the manufacturers millions of £ spent on aerodynamics testing, quite literally goes out of the window.

ER its a skoda felicia ee state
these didnt go in wind tunnels
they used a house brick in front of a vent axia fan

s_b

aloiseb wrote: »

I've searched but can't find any answers so far to the question....

How much more petrol do you use when driving with the windows open, rather than closed? Does it make any difference, how many windows are open, and how far down they are wound?

It can't be just me with a back seat full of children feeling car-sick if the windows are not down......am I right in telling them they are costing a lot more in petrol?

Also wondering, as our car (ancient Skoda Felicia estate) has a wind-up sunroof which comes up at an angle to the car roof, would it be more economical to open that than the windows? It has fixed on roof rack too which I would hate to take off in case it made the car fall apart, never mind the drag.

Please, can anybody point me to any realistic facts and figures about this? I don't mean tests for posh whizzy cars....I mean realistic ones with clapped-out family cars.

It could at least sort a very ongoing family argument.:D

on this car the rear tailgate corrodes badly and it is quite possible the rear window will blow out if you exceed 40 mph with all windows down

almillar

I'm very impressed that rrf was able to calculate all of that without any mention of speed....
Anyway, yes, opening the window causes extra drag. If it's open fully there's more drag than if it's open a little bit. If it's open when you're driving fast, there'll be much more drag (drag squares with speed) meaning a bigger dent in economy the faster you go with the window open.
Therefore at low speed (say below 40 then as above), don't worry too much about windows, but my preference at all times would be to angle the sunroof, as it just seems more aerodynamic to me.

Marco_Panettone

You also need to factor in weight. It'd be cheaper to leave one of the kids to walk...

worried_jim

Lum wrote: »

This thread isn't about windows down vs aircon, something that was covered pretty well on Mythbusters a few years back.

This is about windows down vs making your child suffer and then puke all over the back seats.

Windows down it is.

http://dsc.discovery.com/videos/mythbusters-air-conditioning-vs-windows-minimyth.html

Premier_2

aloiseb wrote: »

I've searched but can't find any answers so far to the question....

How much more petrol do you use when driving with the windows open, rather than closed? Does it make any difference, how many windows are open, and how far down they are wound?

It can't be just me with a back seat full of children feeling car-sick if the windows are not down......am I right in telling them they are costing a lot more in petrol?

Also wondering, as our car (ancient Skoda Felicia estate) has a wind-up sunroof which comes up at an angle to the car roof, would it be more economical to open that than the windows? It has fixed on roof rack too which I would hate to take off in case it made the car fall apart, never mind the drag.

Please, can anybody point me to any realistic facts and figures about this? I don't mean tests for posh whizzy cars....I mean realistic ones with clapped-out family cars.

It could at least sort a very ongoing family argument.:D

How far did you search?

Turn off air con at lower speeds.
Efficiency Improvement: Up to 8%

Air conditioning uses an incredible amount of fuel, so make sure it's turned off unless you really need it. The general consensus is it's more efficient to drive with the windows down and the air con off at lower speeds, but at higher speeds it's better to use the air con and keep windows up due to the extra drag caused by having windows down.

If you're not using your air con, it's worth turning it on once in a while as not using it can mean it stops working.

Also, don't keep the engine running. Drive off as soon as you start up and switch off the engine as soon as you reach your destination.

http://www.moneysavingexpert.com/travel/cheaper-fuel#drive

fivetide

I remember my Dad having a Renault 25 years ago, proper 80's style wedge but the handbook was quite green for the day.

It had a section on fuel economy (and a green line for the most efficent rev range on the dash) which said that over 56mph there would be a 10% drop in fuel economy with the windows open.

Not seen the same claims with any other car I've owned.

5t.

aloiseb

Thanks rrf494g, I reckon your answer will quell family discussion in all but the most smararse teenagers.;)

Premier, yes of course I've read the MSE fuel efficiency page. My question was about having the windows open, not about windows v aircon, which I haven't got in my Skoda Felicia estate.

BTW I hope they didn't test it with a brick: I doubt it would have survived.

worriedjim, Thanks v much for discovery channel video link - interesting, although I wish they had done the test one more time without aircon and with windows shut, and see how many laps they did. As I haven't got aircon.

I think DD who won't take her jumper off (she was too hot, which was why she insisted on having window down) may find herself paying a small surcharge off her allowance if she persists in turning car into wind tunnel test on motorway again. 10% extra fuel seems to be the consensus: I make that £1 per journey to Gran's. And that's not even factoring in wear and tear on the other passengers.,....

And before you all call me a skinflint, yes of course they are allowed the window open if they feel sick! - ie on bendy roads. Our kids don't feel sick on straight fast roads.

red_eye

worried_jim wrote: »

Be comfortable when you drive, why make you passengers suffer for 1mpg. I've heard that windows down below 40mph and windows up and aircon on above 40mph.

makes sense. drag is porpotinal to square of speed
so drag goes up faster then speed and drag starts at around 40mph