Afternoon All,

Can I please ask for an ST3 owner for some help please.

Could you kindly put Cruise on with AC off @ 70MPH with the windows down and let me know what the MPG figure is,

And then repeat with the windows up but AC on at the same speed.

Had bit of a row today over which uses more fuel, can't test myself as no cruise / pauper spec car.

I realise I don't have an ST(3), however have always read that at 30mph or below it is more efficient to have windows down A/C off, then above 30mph (e.g. 70mph) it is more efficient to have windows up A/C on.

I'll be interested to see if someone can test (or has tested) the theory though.

Go on matt which side of the row were you on?

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I realise I don't have an ST(3), however have always read that at 30mph or below it is more efficient to have windows down A/C off, then above 30mph (e.g. 70mph) it is more efficient to have windows up A/C on.

I'll be interested to see if someone can test (or has tested) the theory though.

Mythbusters on discovery channel did once, I can't remember what the outcome was though

I think the windows down will use a huge amount more fuel in real life, whether the CPU will tell is a different matter.

AC I have always thought is a flat 5%.

I remember the myth Busters, drifting a lorry was something stupid like 18% more efficient.

.

Matt I shall have a crack at this on the way home in about 40 mins :P

Mythbusters on discovery channel did once, I can't remember what the outcome was though

i remember this one it was busted the air coming into the car did nothing at all but with air con on it did bring the figure down the windows down didnt cause enough drag at all to slow car down enough to use more gas (petrol)

I've always thought it's about the same fuel consumption.

Either ac on or windows down. I have tried both and still put the same amount of fuel in each week on my work run, same route day in day out.

Sorry didn't get overy 45 on the way home dam Friday traffic :(

Surely it's more important to be comfortable rather than worrying about mpg. Unless your travelling hundreds of miles it's not going to make too much difference. I like it cold in the car rather than windy but sometimes like to get fresh air in.

Also windows open at 70 is just too noisy for me.

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At low speeds windows down will be best (with fans running without aircon switched on).

At higher speeds aircon running with windows closed is better.

I love having the windows down, in a month or so we won't be able to for god knows how long so got to make the most of it, I know the window option will be more uneco but was wondering if the trip will actually show this.

Yeah mate it will reflex lower mpg.

At higher speeds the engine generate so much energy that some becomes waste energy, in those circumstances it has more energy than the ac would use therefore it does not affect mpg.

At lower speed or idling there isn't enough energy, your car will need to create that in order to run the ac by using more fuel

Recently my fuel consumption has been high because of ac, I run that bad boy 24/7 windows closed, super dry air inside the car

An important thing to remember is the car doesn't cut through the air as cleanly when the windows are down hence the fuel consumption. But as stated multiple times, AC is best at high speeds over windows.

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