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Mr Xtrail Profile
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X-TRAIL FANATIC
 


Date Registered: 12-2008
Location: Sydney
TOTAL POSTS: 392
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Re:


Translucidus I think I understand you post above although still have just question, as the high pressure air is reduced due to the exy being higher and the air flow under the car increased, would this give us exy drivers a higher or lower chance of the car being thrown around on the highway at high wind areas? im guessing an even lower chance as it is low pressure air.

I havent had a chance to get under my exy to see the air dams to get the size and see if its on an angle as suggested above, although I will try and do this in the next day or so.



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2008 T31 TL DCI 6 Speed Manual X-Trail (x-1083)
with JAOS Strut Bar, K&N filter, Mats, Rubber Boot Liner, Tints, Cargo Barrier, Towbar, glove box light, dashmat, Geo ATS 225/60/17 & now with babyseat

6/Oct/2010, 8:24 am Link to this post Send Email PM   Send Private Message
 
Translucidus Profile
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X-TRAIL LEGEND
 


Date Registered: 05-2010
Location: Adelaide
TOTAL POSTS: 599
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Re: Front Wheel Air Dams


I understand that some aerodynamic solutions are counterintuitive, but air flow is a complex field of research, and "Mind Experiments" and reasoning are unable to solve or understand many aspects. There are so many variables involved and many of these are obscure eg raise the body and drag on the body is reduced but overall drag may increase or decrease depending on the increased lower wheel area exposed and how wide or narrow the tires are and some other factors such as is the lower body below the centre line of the wheels or not!!!

Although I'm not an aerodynamics expert, have just researched and experimented a lot and found some things that work for me.

With that in mind here goes:

With regard to cross wind and high winds generally, the addition of front wheel air dams (and any smoothing of any surface of the car ie underbelly) will reduce the impact of these factors. The underbelly is not seen by the consumer, so most designers haven't bothered to give it aerodynamic treatment until recently.

The air dams do this by preventing some air entering the wheel wells (that are an aerodynamic disaster area). The higher the car, of course, the more lower wheel area is exposed and so the higher the additional frontal area caused by more wheel being exposed (wider wheels bad, narrow wheels good from a drag perspective).

The higher the car the less the ground effect and there is a drag reduction on the body, but a drag increase caused by more exposed wheel area.

It's all quite complex and change one aerodynamic aspect eg at the front, and things change elsewhere for the good or bad (only wind tunnels show the whole picture from any change).

For a good example of aerodynamics from a drag (better fuel mileage) and performance in all wind conditions look at a new Camry (CfD of about .28, very low) and its features eg smoothed underbelly , wheel air dams, sharp rearward cutoffs, relatively narrow tires etc etc.

For an XTrail there probably isn't much room for improvement aerodynamically beyond some underbelly smoothing and the wheel air dams and perhaps removing or covering with a rear bash plate, that rear lip that catches in the sand and rips off the bumper.

The higher the car remember, the more "Leverage" a cross wind has on the higher body, but the less the drag caused by "ground effect".

It's all a balancing exercise between form, function and what the car needs to do.

If your Xy has the small front air dams, they would be fine for a 4WD car given water crossing loads on the plastic and the compromise needed here. Mine have been OK so far with water crossing, so there you go.

Last edited by Translucidus, 6/Oct/2010, 4:37 pm


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2007 X-Trail T31 ST-L

Xy going vertical at Bendleby Station . . .

6/Oct/2010, 4:29 pm Link to this post Send Email PM   Send Private Message
 
oldbeach Profile
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X-TRAIL ENTHUSIAST
 


Date Registered: 12-2008
Location: Tasmania
TOTAL POSTS: 110
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Re: Front Wheel Air Dams


Hey Guys

All very interesting. I have an item you may want to consider. You have all seen the flared guards on most 4 X 4s. This is simply a rubber strip with a flange on one side and a 100mm strip on the other. A friend of mine has this on his car as side skirts and front lower spoiler.

Pros, very easy to attach, screw through flange to body. Rubber easy to shape with cutters or sharp knife. Flexible good for us 4X4s.

Could be a suitable alternative to using a plastic strip, also cheap @ about $6.00/M

sample.
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Cheers
Les

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Les X-1074
T 31, Black, Bonnet protector, TowBar, Reverse Park, Cargo Tray, Angel Eyes
7/Oct/2010, 9:57 pm Link to this post Send Email PM   Send Private Message
 
boodz Profile
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X-TRAIL NEWBIE
 


Date Registered: 10-2010
Location: the GONG
TOTAL POSTS: 11
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Re: Front Wheel Air Dams


thought i would post this just incase anyone is interested...
i personaly belive it to work, because alot of new cars and the t31 diesel has them too.
so i ordered the ones off the diesel and they fit perfectly and they only cost $36 for both of them... all you need is 4 x 6mm bolts to mount them.i also used pannel washers and lock nuts to prevent vibrating loose... emoticon

part numbers are...
63844-jg00A (protector right hand side)
63845-jg00A (protector left hand side).

these are genuine nissan so if any are to work these will.
i will test them out in feb. 2011 when i go to see family 10 hours drive away. emoticon

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Last edited by boodz, 6/Jan/2011, 8:42 am


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Bowden A Grace
this is my missus automobile, (that i steal) a 2008 st t31
6/Jan/2011, 8:26 am Link to this post Send Email PM   Send Private Message Blog
 
Translucidus Profile
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X-TRAIL LEGEND
 


Date Registered: 05-2010
Location: Adelaide
TOTAL POSTS: 599
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Re: Front Wheel Air Dams


Fantastic Boodz - a lot easier to make and fit and if one breaks you can buy another one.

Size & shape may have even been optimised in a wind tunnel - then trimmed by stylists and shrunk until they don't break in water crossings and get caught too much in the scrub.

They look just fine to me emoticon

 emoticon

Last edited by Translucidus, 6/Jan/2011, 9:32 pm


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2007 X-Trail T31 ST-L

Xy going vertical at Bendleby Station . . .

6/Jan/2011, 9:29 pm Link to this post Send Email PM   Send Private Message
 


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