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Discussion Starter #1
Hi everyone, been lurking on these forums for a while and have recently purchased a 2016 1.6 DTEC SR, after all the positive reviews I read on the 9G and the diesel engine.

So far I’m really enjoying it - the great engine along with the high spec make it really fun to drive. Performance and economy have both been great and hopefully reliability will be as good as my old 7G.

However, with the recent bad weather, I’ve noticed the mpg drop dramatically when driving down the A30 here in Cornwall and straight into a headwind. Would usually be getting around 55-60mpg in that direction but today and earlier in the week I’ve been down to 45-50mpg. Don’t think it’s been doing a regen either time and the fan hasn’t been running after each journey, which is usually a tell-tale sign. On both occasions the wind was high and almost head on or sideways so I’m guessing it’s more than coincidence.

I know this generation was heavily tweaked when it came to aerodynamics and drag in order to achieve greater efficiency, but could that be working against it when the airflow is disrupted by high wind (50-60mph), particularly when it’s head on?

Curious as to whether anyone else has experienced this or if it might actually be something else?
 

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The aerodynamics on the 9 / 10G Are rather wizard:- You've got a 0.27Cd on the 9th Gen in standard trim; The new Focus released in 2018 has a 0.275Cd with the addition of air curtains for the wheels, active radiator flaps and all manner of improvements. - You can tell Honda got the F1 engineers on board!

When it comes to headwinds, the lower drag of course helps, but it's overshadowed by physics. Drag increases exponentially with airspeed, which is why driving at 100Mph requires so much more power / fuel than 70; And why it takes something very special to get over 200Mph.

In essence, with a constant 50mph headwind, and a road speed of 70mph, the aerodynamic drag forces would be equivalent to those experienced at 120mph (Though of course, It's very rare to get a truly constant speed of headwind)

Similarly, If you have a constant tailwind on the way home, you'll have less drag - And better fuel economy!
 

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Not forgetting throwing winter diesel and the cooler temperatures into the pot. All combine to spoil your fuel returns. Mine always drops during winter but regains some decency once the temperature climbs back up.
I’d check your tyre pressures just to eliminate those as a possible cause but obviously a strong headwind won’t help your MPG returns. Plus don’t trust your computers MPG displays, it’s usually off by a good 3-5 MPG.


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When I first got my tourer I took a long trip (150+ miles) and was disappointed with the economy, later looking at the weather maps I could see I had been driving into a headwind

Other times the same journey yielded far better economy so the conclusion I came to is that yes, the Civic is very affected by wind. No idea if the tourer and hatch are different in this respect though
 

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Discussion Starter #6
Thanks everyone. Seems the Civic can be quite sensitive to these things, more so than my previous Auris was but I know they’re very different cars.

Going the opposite way today, and with somewhat less wind behind, the mpg was up into the low 70s, so can’t complain too much really!
 

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Drive into a gale force headwind with bikes on the roof in my mk8 diesel civic. The fuel economy was dropping so fast that I thought I had a fuel leak. I think after 2 hours it was down to 32 mpg! And that was in the very flat A11.

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I wonder if this is how Honda got 100mpg on that tourer. They checked the wind direction every morning and drove wherever they had a tail wind


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