All Things Mk5 > Performance Modifications
improving aerodynamics with OEM parts
the bruce:
Well, I like my coil over, my ARBs, my wheels and so on much more,
but these underside parts are some bit cheaper, Robin.
Placing the battery isn't easy, I know. There is a nice place for the
battery in the rear in the 4-motion models that we sadly don't have.
That's why I replaced my spare wheel with the compressor kit. One
more reason: saving little weight.
Second is the cabling. Using OEM cables is very expensive.
RedRobin:
--- Quote from: the bruce on February 03, 2011, 01:32:44 pm ---
Well, I like my coil over, my ARBs, my wheels and so on much more,
but these underside parts are some bit cheaper, Robin.
--- End quote ---
Cheaper yes, but what benefits do these aero underbits actually have in reality? - Did you read cmdrfire's reply about downforce and diffusion?
--- Quote from: the bruce on February 03, 2011, 01:32:44 pm ---
Placing the battery isn't easy, I know. There is a nice place for the
battery in the rear in the 4-motion models that we sadly don't have.
That's why I replaced my spare wheel with the compressor kit. One
more reason: saving little weight.
Second is the cabling. Using OEM cables is very expensive.
--- End quote ---
....Personally, even though some of my mods have saved weight, I'm not on a mission to save weight. If I really wanted to save overall weight I'd do at least a partial strip out. And I certainly don't want to compromise my load carrying ability.
cmdrfire:
If you want to save weight, don't buy a Golf...
Snoopy:
--- Quote from: Aaron_RJ on February 02, 2011, 10:11:52 pm ---Is a fixing kit you dot need to use It though just use some self tapping bolts m8 thread
--- End quote ---
--- Quote from: the bruce on February 02, 2011, 10:45:02 pm ---I had the bolts from VW, but don't hesitate and use some standard ones.
Just take care it's zink plated or similar.
--- End quote ---
--- Quote from: RedRobin on February 02, 2011, 10:46:57 pm ---....I think stainless steel bolts would probably be best of all.
--- End quote ---
--- Quote from: RedRobin on February 02, 2011, 11:08:22 pm ---
--- Quote from: the bruce on February 02, 2011, 10:59:53 pm ---
I try to avoid shiny bolts on, in and under the car (with the exception of exhaust).
--- End quote ---
....Any particular reason?
My thinking would be to achieve the best durability. Titanium might be rather expensive!
--- End quote ---
Thanks guys. I will use stainless steel bolts as we use loads of them at work so they are easy for me to get a hold of. Plus the underside of my car has loads of waxoyl on so there shinyness will not show after i do them too.
the bruce:
--- Quote from: RedRobin on February 03, 2011, 02:25:42 pm ---Cheaper yes, but what benefits do these aero underbits actually have in reality? - Did you read cmdrfire's reply about downforce and diffusion?
--- End quote ---
This one?
--- Quote from: cmdrfire on January 14, 2011, 06:41:49 pm ---As a note, maybe 10-15% of an "eco" car's efficiency gains are from improved aerodynamics on the underside.
Remember though that increases in aerodynamic downforce also result in increases in drag, making the vehicle less efficient and and reducing vmax.
Undertrays designed to reduce drag will not, in my opinion, improve high-speed stability.
--- End quote ---
I don't agree with this.
The stock underside of the GTI creates both, drag and lift.
But before explaning the reasons in bad English it would be easier you read some
scientific material. I've read the very most of it:
http://www.informaworld.com/index/780901753.pdf
http://elib.tu-darmstadt.de/tocs/133153142.pdf
http://www.buecher.de/shop/dynamik/aerodynamik-des-automobils/hucho-wolf-heinrich-hrsg-/products_products/detail/prod_id/14466476/
http://www.atzonline.de/Fachmedien/Buecher/4/132/Aerodynamik-des-Automobils.html
http://libros-en-pdf.com/descargar/aerodynamik-des-automobils-3.html
http://ieeexplore.ieee.org/iel5/4588253/4601965/04602075.pdf?arnumber=4602075
http://www.spiegel.de/auto/aktuell/0,1518,673321,00.html
http://www.fl-automobil.de/page-m_ge_die_kraft_Was_ist_Abtrieb-12.phtml
Feel free to find even more of this stuff in English. The conclusion will be the same:
A flat underside will always reduce drag and lift. Believe me. :wink:
Without a wind tunnel we cannot state the amount of improvement but it it will be
an improvement. Flatter is better in this area.
We cannot exactly state the resulting lift front and rear (but I promise at 200 km/h
it's around 0 front and 250 N rear). No downforce of course, but better than stock.
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