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

aloiseb

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

LandyAndy

The reality is that it is costing you something but not as much as having the interior cleaned if one the sprogs pukes.

rrf494g

I think the figures for . . .
Ancient Skoda Felicis Estate
2 Adults in front
3 Children in rear
2 big suitcases and 3 holdalls stuffed in boot
26 psi tyres at front and 28 psi in rear
Normal extended radio aerial (fully pulled)

---

Each front window costs extra 1.352 miles per gallon fully down
Each back window costs extra 1.002 mpg
Sunroof (alone) costs 0.745 mpg OR 0.634 mpg in conjunction with at least two other lowered windows
Roofrack costs 1.563 mpg or 1.653 if with open sunroof
BUT
This all assumes zero windspeed. If travelling "with following wind" the mpg losses are reduced by a factor= windspeed (in mph) /squareroot of rolling mass of car (in cwt) * air temperature(c)

If there is a headwind, the factor to increase the mpg loss figures is = windspeed (mph) /time(in mins) since last "are we there yet" question* percentage of picnic alraedy eaten

hope this answers family discussion

vaio

I got 1.357 mph for the front windows

Trebor16

It only starts to make a real difference when you get above 40mph. Below that speed it won't affect the economy that much.

Stephen_Leak

I always thought it was allegedly and infinitesimally better with the windows up. Cleaner airflow, etc.

forgotmyname

Windows down causes drag, The argument is usually which uses less fuel windows open or aircon on.

Windows open at low speeds affect economy very little, Aircon on at high speed doesnt affect economy as much as it does at low speeds.

Strider590

Stephen_Leak wrote: »

I always thought it was allegedly and infinitesimally better with the windows up. Cleaner airflow, etc.

This......


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

worried_jim

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.

funkycoldribena

rrf494g wrote: »

I think the figures for . . .
Ancient Skoda Felicis Estate
2 Adults in front
3 Children in rear
2 big suitcases and 3 holdalls stuffed in boot
26 psi tyres at front and 28 psi in rear
Normal extended radio aerial (fully pulled)

---

Each front window costs extra 1.352 miles per gallon fully down
Each back window costs extra 1.002 mpg
Sunroof (alone) costs 0.745 mpg OR 0.634 mpg in conjunction with at least two other lowered windows
Roofrack costs 1.563 mpg or 1.653 if with open sunroof
BUT
This all assumes zero windspeed. If travelling "with following wind" the mpg losses are reduced by a factor= windspeed (in mph) /squareroot of rolling mass of car (in cwt) * air temperature(c)

If there is a headwind, the factor to increase the mpg loss figures is = windspeed (mph) /time(in mins) since last "are we there yet" question* percentage of picnic alraedy eaten

hope this answers family discussion

Your figures are wrong by 0.012.

Lum

forgotmyname wrote: »

Windows down causes drag, The argument is usually which uses less fuel windows open or aircon on.

Windows open at low speeds affect economy very little, Aircon on at high speed doesnt affect economy as much as it does at low speeds.

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.