Open windows or air con?

[Miss D Meanour]

Ok guys - don't shoot me down in flames if this is a stupid question -

What's more damaging to my fuel economy? Driving around with the air con on or having my windows wound down?

[kambites]

There's a crossover speed. At low speed, the aerodynamic drag caused by having the windows open is negligible but at motorway speeds it's huge, whereas aircon draws the same amount of power for a given cooling effect at any speed.

Not sure what the crossover speed is, but probably somewhere around 40-60mph depending on the car?

[V88Dicky]

Mythbusters covered this in one of their shows iirc. Up to about 40mph it was more efficient to have the windows open. After that, it was better to run the aircon.

[Mars]

Depends on speed and how often you accelerate. Opened windows will be more damaging to your fuel economy at higher speeds, whereas if you accelerate while the aircon pump is engaged, you will use more fuel than when it engages during a steady-state speed.

Never a simple answer is there?

[BoRED S2upid]

The standard PistonHeads answer is who cars you will be driving flat out all the way with the roof down if you have a convertible even in the winter.

[mmm-five]

My aircon disconnects on full throttle to give me that all important extra 5hp

[anonymous-user]

mmm-five said:

My aircon disconnects on full throttle to give me that all important extra 5hp

Most cars do that, at WOT they disengage. If you suffer from hayfever then A/C is a god send..........

[BrewsterBear]

If you have aircon and drive with the windows down then you're either too tight to get it fixed, or should it be working, Scottish.

[roachcoach]

Am I the only one who prefers the window down?

I feel more engaged/less enclosed that way.

[char5]

BrewsterBear said:

If you have aircon and drive with the windows down then you're either too tight to get it fixed, or should it be working, Scottish.

I have AC, but I drive with windows down a lower speeds (not on motorway as it's too noisey), might aswell make the most of the nice weather when we get it in the UK.

[jsg612]

Always have the window down unless on a motorway. Aircon gives me a sore throat.

[andy-xr]

I was wondering this yesterday! 150 mile round trip up and down the M1 and paying for my own fuel makes you think that little bit more!

I went with windows open to the height of the wing mirrors at 60 and seemed to get fairly good economy (58 mpg, Focus C-MAX 2.0 diesel)

[Riley Blue]

Summer or winter my Audi's A/C rarely goes above 18C. The only time my car's window goes down is at the Dartford toll.

[anonymous-user]

BrewsterBear said:

If you have aircon and drive with the windows down then you're either too tight to get it fixed, or should it be working, Scottish.

[egomeister]

Dave_ST220 said:

Most cars do that, at WOT they disengage.

This could explain why my aircon doesn't seem very effective

[Fire99]

Air Con is not the most lovely thing for your health. Nice to have when stuck in traffic on really hot days but for normal stuff, Window is just fine for me.

[Hysteria1983]

I think it's already been answered.

In my Subaru, I hardly used the ac, the mpg wasn't exactly economical anyway. Luckily I had a sunroof too.

Ironically one of the few times I had to use the ac was in a bit of a traffic pile up last summer. The car overheated after 20 mins stationary so I had to open all the wu down and put the heating on. It was horrific.

Now I have a lupo, with no ac or su roof

Edited by Hysteria1983 on Tuesday 2nd August 10:25

[anonymous-user]

doogz said:

But apparently this is normal because i'm Scottish? Not quite sure why that makes a difference.

It doesn't. If you don't get the intended humour then you'll shortly be accused of having a chip on your shoulder, don't worry, it's the norm in here sometimes, and gets really fking tiresome.

[Y282]

wow, the answer to this one really IS mx5!

the things you see if you hang around long enough...

[Corsair7]

V88Dicky said:

Mythbusters covered this in one of their shows iirc. Up to about 40mph it was more efficient to have the windows open. After that, it was better to run the aircon.

Surely this depends on the outside air temperture...? If its 35 degree C outside theres little point in having the windows open at low speed.