Aerodynamics

dillosk8ter · Post by **dillosk8ter** » 12 Aug 2005, 20:33

Does anyone know how aerodynamic the ZX is i.e. cd 0.??. I've been wanting to know since I bought mine 5 years ago and haven't been able to find out anywhere.

Ross_K · Post by **Ross_K** » 12 Aug 2005, 21:19

0.33 apparently...
http://www.carfolio.com/specifications/ ... /?car=5984

oilyspanner · Post by **oilyspanner** » 12 Aug 2005, 23:17

Interesting site, found a BX ! CD 0.34
Stewart

dillosk8ter · Post by **dillosk8ter** » 13 Aug 2005, 00:31

Think DS was 0.36? might be wrong.

James.UK · Post by **James.UK** » 13 Aug 2005, 01:01

I think the Volcane with its flatter deeper front lower skirt would create more drag than the other ZX models.. So the figure may well be lower than 0.33 for most ZX's... [:)]
Hmm... So how much could be gained by curving your front number plates? widthwise I mean, not lenghtwise, and how could this be done? Heat? but how to bend it? press it against a piece of hot pipe? Any ideas?
Other than the number plate most of the front end is already fairly curved (ZX).. Change door mirrors for more aerodynamic ones maybe? but what would fit? Incidentaly most of the wind noise in my ZX is caused by its door mirrors.
.

dillosk8ter · Post by **dillosk8ter** » 13 Aug 2005, 01:13

Same here James. Not suprised the ZX has a decent drag co as the body looks pretty streamlined and smmoth especially when compared some of its contemporaries e.g. Escort

Ross_K · Post by **Ross_K** » 13 Aug 2005, 04:49

The worst source of wind noise on my ZX would have to be the sun roof...

howiedean · Post by **howiedean** » 13 Aug 2005, 12:17

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Ross_K</i>

The worst source of wind noise on my ZX would have to be the sun roof...
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Or that stupidly large aerial just above it. [:D]
Regards

jeremy · Post by **jeremy** » 13 Aug 2005, 13:11

I'm not surprised that the ZX has a drag figure of .33 - it explains why they go so well over 70 on 71 BHP. My BX estate is noticeably worse and feels much harder work - and indeed probably ultimately is no faster.
I had a Renault 21 (early one) with an amazing drag so-efficient of .30 if I remember correctly and although the thing looked like nothing on earth the attention to body detail was amazing, with deep rear bumper, nearly flush glass, neat door handles etc. This car was extremely fast over 80 and I have no doubt would have achieved the claimed 113 on 1721cc and 90 BHP. If you lifted off at 80 the thing felt as though it would run for ever with no engine! It was also very economical at speed and I recall finding that it would do 43 on long runs at moderate speed (cruising at 80+ and acelerating quite hard). Round town it was the same as everything else - very expensive!)
jeremy

James.UK · Post by **James.UK** » 14 Aug 2005, 01:35

Ross, check that your sun roof it closing right down flush, I get very little noise from mine.. You could also add some tar backed flashing to the back of the internal cover if you have room on top. That might help as well. [:)]
Howie.. Tip the aerial back to about 38 degrees above horizontal to minimise any noise, and try the flashing as suggested above.. [:)]
.

Ross_K · Post by **Ross_K** » 14 Aug 2005, 02:01

Thanks James, I'll check that out. I have a feeling it isn't quite flush. One more job to add to my list of things to do... [8D]

tomsheppard · Post by **tomsheppard** » 14 Aug 2005, 15:45

Aerodynamic drag figures are like manufacturers' MPG figures- fiction mostly.
For the record, CDa DS.36, CX.35, BX.34. BX estate below BX saloon. (It is longer.)The ZX won't be far ahead on aeros. A TZD estate will do 120MPH on 90BHP once run in. It isn't just light but slippery, too. Surprisingly the shape of the car is 85% of the drag and mirrors, aerials, bumpers etc contribute only 15%. Comforting when you consider the BX's elephant ears.

oilyspanner · Post by **oilyspanner** » 14 Aug 2005, 16:54

I suppose having fat wheels and tyres doesnt help either, and I have found my BXes sensitive to a roof load, even a pair of oars strapped to the otherwise bare roofbars used to have a significant effect on the top end, it was more noticeable with the old 1769 motor, the 1905TD seems to push the air out of the way even with my giant roof box on, though at the expense of more diesel going in.
Stewart

FrenchLeave · Post by **FrenchLeave** » 16 Aug 2005, 04:01

The major influence on drag coefficients seems to be the rear end. I once did a demonstration by puting a standard aerofoil section (RAF148) the right way round in a low speed wind tunnel, the calculated Cd came out at 0.12. I then put it in trailing edge first and repeated the test. It looked very streamlined with its wedge shape but the calculated Cd was 0.25. The reason for this was that the airflow the right way round was laminar over its whole length, whereas the arse forwards section became turbulent immediately after the point of maximum thickness.

fastandfurryous · Post by **fastandfurryous** » 16 Aug 2005, 04:40

This is very true, it is the convergance of the airflow at the back that has the greatest effect on aerodynamic drag. It's the main reason an estate car is less fuel economic than a hatchback car. The odd thing is that if you take most cars on the road today, and drive them in reverse, they would be more aerodynamic. Take a Pug 306 for instance. Far more aerodynamic in reverse than going forwards.
This is most noticeable on cars that have been designed by aerodynamicists. Look at a Porsche 911 (early models) or a Saab 900. Quite bluff fronts, but gently tapering at the back.