Thame Driving Blog

    Windows down or air con on? Which is best from a fuel economy perspective?

    Thame Driving Blog

    About 2 years ago I was approached by several customers about information that we know as "motor industry experts" but is unknown to the wider public.

    I thought that knowing what to do to pass your MOT or how to claim money back if you hit a pothole was easy information to find. Apparently not, and anayway when it comes to cars and motoring, what I have found is that there is alot of guff and untruths out there. The feeling I got was that people want to listen to people that they trust.

    So....I started writing articles about useful motoring information, amusing tales and local information. I now send this out to over 2,000 people on a monthly basis along with other motor related emails and generally get really good feedback. In fact what happens now is that my readers are now telling me what to write about.

    I hope you enjoy the articles and if there is a particular topic you want to know about then please let me know.


    It’s the classic car conundrum isn’t it?

    With the mercury rising we’re doing everything we can to not complain about how hot it is, so it’s great that we have a couple of cooling options when we’re in the car.

    We can wind down those windows or crank up the air conditioning to blast arctic air into the cabin.

    But which is best from a fuel economy perspective?

    We asked Thame’s fitness expert George Anderson for his take on the conundrum.

    Why would a fitness guy know anything about it? 

    Before he moved into fitness George studied for 5 years at Loughborough University for a masters degree in automotive engineering, and has apparently spent 'many a happy an hour tinkering about in wind tunnels'.

    Yes, that’s what we thought as well.

    Here’s what he had to say…

    “The answer is ‘it depends’. 

    It depends on the kind of car you’re driving, the speed you’re driving at, the direction of the wind, ambient temperature, and how much you want to cool it down.

    Thanks to the laws of physics the faster a vehicle is moving the more significant aerodynamic forces become.

    Winding down your window creates a kind of parachute effect, which means your engine has to work harder to maintain the same speed.

    Harder work = thirstier engine = less fuel efficiency.

    A typical air con unit is going to reduce fuel economy by about 10%, but if the windows-down-effect is going to drop it by 20% on the motorway, you’re better off with the chilled air.

    On the other hand, if you’re driving a people carrier, SUV or other aerodynamically suspect vehicle, the effect of dropping your windows probably won’t add a significant amount of inefficiency to the equation.

    If it’s hot outside, windows down is going to just suck in a warm, muggy breeze of pollution and noise.

    Which brings us onto personal preference.

    Even if you could save a couple of quid on a tank of fuel by rolling your windows down, that might not be the ideal way for you to keep cool.

    Noise, ease of control, feel of the air con and sense of privacy…

    These are all factors you need to take into account and weigh up against the potential savings.”

    Thanks George, personally I like to start off with the windows down and then switch to air con after a few minutes.

    Good to know that with so many variables, including personal preference, it’s not worth worrying about!