You might remember as a kid trying to turn AC on in your parents’ car and getting the scolding of your life. “Do you have a secret stash of fuel somewhere that we don’t know about,” came the rebuke. It was ingrained in our minds from an early age, you don’t use AC, you roll down the windows.
With summer upon us, you might want to know just how good that advice is. Turns out, that age old wisdom is solid. It really is more fuel efficient to roll down your windows than it is to use the aircon. However, that’s not where it ends. There are nuances.
The Society of Automotive Engineers (SAE) conducted a study a while back that showed that it is more fuel efficient to roll down your windows up to around 70km/hr. Of course it will be different for different cars but as a rule of thumb, 70km/hr is the golden figure.
When you exceed that speed, the drag caused by the open windows will increase fuel consumption more than turning on AC would.
Using the aircon can increase fuel consumption by 10%. That’s a lot. However, rolling down the windows at higher speeds can increase consumption by up to 20%.
To note is that this applies more to sedans than to SUVs and other aerodynamically challenged vehicles. Turns out SUVs already have so much drag that rolling down windows at high speeds doesn’t do much. In some studies, rolling down windows was more efficient than using the aircon in SUVs even at high speeds.
So, generally put, city driving is windows down but highway driving is aircon territory. You will find studies that say windows down is better at any speed for any type of vehicle so just know the debate is far from settled.
The fan
There is another option. The fan on but AC off option. This won’t result in any significant increase in fuel consumption because the fans will be run off the batteries just like the stereo. The aircon involves running a compressor off the engine hence why it increases fuel consumption.
This method won’t cool you as well as rolling your windows down will. The small fans can’t compete with the volume of air that rushes in from the windows. However, the fans may be the only option when the air outside is polluted and you’re in stop-go traffic.
In that scenario, the humble fan is your best option. You just need to make sure you set your dials to recirculate cabin air and not allow air from outside the car. The effectiveness of the fans will depend on how hot it is, you must know how fans can be ineffective when they are pushing hot air around.
Heating the car is easier though as the engine produces a lot of heat and that can be channeled to the cabin. Heating is as good as free.
So, on those rainy days when it gets a little chilly, you don’t have to think twice about turning the heat on. The fans will have to push the hot air in but we have already established that fans are efficient.
If you have a newer car it’s not as clear cut. You may not have the ability to manually turn fans on with AC off.
Live like a king/queen
There you have it. Don’t sweat like a pig, drive in comfort without breaking the bank. Heating is practically free as are fans with AC off.
As regards the other thing that would get you a good spanking – turning the cabin light on at night – the parents might not have been that spot on. You have no doubt heard that the cabin light should be off when you’re driving at night.
The logic is, it is hard to see into the darkness when you yourself are in the light. Try peeking outside your window at night with the light on in your room and see how difficult it is. However, if you point a light into the darkness, it doesn’t matter much that you are in a well lit room. You can see well enough.
This means the cabin light issue is simple, unless the light distracts the driver there’s nothing to worry about. Except maybe privacy. In some cars the position of the light, coupled with the slant of the windscreen may result in some glare in the driver’s eyes.
Clearly, in that case it would be unwise to turn it on. If not though, you can have your passengers read books from the cabin light, it’s okay.
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16 comments
That then begs the question of how effective are open windows with aftermarket wind deflectors. There has to be reason why they are so popular, or are they a wives tale grade accessory with a powerful placebo effect
Think about it the latest petrol/diesel or electric vehicles on the market not even one has a wind deflector. The manufacturers are obsessed with reducing wind drag and the cars coefficient, testing their cars in wind tunnels etc. This being done in order to raise fuel economy or increase range but somehow they all seem to have missed the very simple idea of wind deflectors?
If they were effective they would not be aftermarket but come with the car from the factory.
So wind deflector effectiveness is most probably a myth.
But they make the car’s look so good!
Some things on cars were removed simply to reduce production costs. It should not be taken to mean ineffectiveness of the features, or increases efficiency of the car. Now, eome cars only have one reverse light, whilst others only have electric windows for the front doors. If wind deflectors cost 5 dollars and a manufacturer produces just 10,000 vehicles, that’s $50,000 saved.
You are sort of proving my point.
There’s not a single electric vehicle with air deflectors but they all come with plastic wheel covers/inserts and lot of effort has been put in to try and make them look better but they are rather ugly looking.
But the reason why are installed at the factory is that these covers are very helpful in reducing wind resistance and lowering the drag coefficient of their cars thereby increasing the range which is very important for electric vehicles. So being able to boast a few extra miles/kms of range over the competition is still very attractive in this relatively new market where more range is still more important than the price difference of $400.
Yet we still can not find a single wind deflector installed from the factory in sight.
So we can only assume that the wind deflectors whilst they might look good were found to be very detrimental to the range and efficiency of these cars.
🤦🏾♂️🤦🏾♂️ $400 for wind deflectors are they made of gold?! 🤣🤣
Even combustion engine vehicles are coming without deflectors, but their design hasn’t fundamentally changed to reflect improved aerodynamics. In fact, a lot of electric cars are built of the same non-electric designs (except the tiny ones).
FYI, window deflectors may actually reduce drag. So there’s more reason to include them.
So we’re to believe that multiple engineers with PhD’s tested new car designs in wind tunnels, did complex calculations using fluid dynamics on Supercomputers resulting in them.
Making the handles flush with the body of the car, replacing the sideview mirrors with cameras and developing low rolling resistance tyres with ugly wheel covers/inserts all in the name of aerodynamic efficiency so that they could boast about how they lowered the drag coefficient by 0.01 increasing range by a few kms/mls further than the car from competitors.
But they somehow left the obvious and low hanging fruit of the already available concept of wind deflectors?
Yes that sounds very reasonable.
That’s not a logical deduction at all. Plenty of car designs are not as aerodynamic as they could be. With many just building on previous designs, hence the latest Hilux and its predecessors have repeatedly failed the Moose test, regardless of how many PhD holders Toyota has.
You are thus generalising things specific to high end sports cars, to mass production vehicles. Even a Ferarri can have no radio, no carpet, no air-con, no door handles and you would deduce that they serve no purpose. Mass production vehicles have always prioritised low production costs over performance.
FYI…. It either does or doesn’t. And from the levels of innovation that has gone into developing full on electric cars the answer is…. It doesn’t
It does reduce drag. These are Googleable things!
https://wadeauto.com/blogs/blog/how-to-improve-the-aerodynamics-of-your-car
It’s true that mass production have always prioritised cost. But this doesn’t apply when we talk about the range on EV’s it’s a fact that no matter how friendly to the environment they may be they are severely lacking in range and the manufacturers have pulled out all the stops trying to desperately eke out a few more extra kms in range to make them more attractive when compared to the fuel driven cars. And the fact that they have completely ignored deflectors means that the gains are not really worth it.
And yes cars still fail the moose test, but that’s down to the laws of physics. Something like the hilux with it’s high centre of gravity is not going to do so well in that test.
Ferrari 11000
Bentley 14000
Lamborghini 8400
Teslsa 930 000
Volkswagen 709,030 China’s BYD Co 595,089 units.
General Motors 515,584 units.
Hyundai Motor and Kia, the two automaking units of Hyundai Motor Group, 348,783 units
Now I know it might not be much compared to the 40 million plus production of normal car but I would argue that it is now mass market when compared to the niche markets of the High end sports cars
Fun fact… In the Moose Test electric vehicles generally tend to perform better than ICE cars, but EVs derived from ICEs are worse
The reference to the Moose test, is not drag related, it is that bad designs are created and continue despite having PhDs holding engineers. Other 4x4s with the same clearance perform margins better on the test.
EVs perform better on the Moose test as a the heavy battery packs lower the centre of gravity, as a side effect, not explicit design.
Deflectors reduce drag, There are even scientific research articles about it 🤷🏾♂️. I don’t see how some EVs not having them means otherwise. EVs are not the gold standard for efficient vehicle design. A significant number of EVs also share the same body as the ICE counterpart. They don’t magically become more aerodynamic, because they are electric.
Whilst a significant number of EV’s maybe based on ICE models. This is because the manufacturers ignored EV’s until Tesla started stealing their market share and they panicked and did conversions to cover the gaps in the short term.
Developing a new clean sheet design from scratch takes time. But I am actually basing my argument on those clean sheet designs cos as I said before range is a very significant problem for EV’s and because it’s such a problem every effort has been taken to address the problem. With quite a few solutions coming up but somehow the simple and low tech deflectors have been ignored
Even the first Tesla was built of an existing ICE car design.🤷🏾♂️
Your original point was deflectors don’t reduce drag, they do. I haven’t found a single article disproving that.
You are also generalising the Tesla 3 design, to cover all EVs. Deducing that since it is very aerodynamic, then they are all aerodynamic. It’s bad logic.
🤣🤣🤣 imi editor dont compare aircon ye honda fit neye subaru or Mercedes ka , i think u comparing fan iripa cold ne aircon, if i drive from harare to masvingo with aircon i waste about a ¼full tank bt without ndakavhura window doing 80km-100 i use half
Yes i understand aerodynamics and wind deflection bt on this opinion i beg to differ , ask anyone ane electric car
Interesting