Rust is appearing in the rear wheel arches under the OEM rear wheel arc trim ( the plastic part is in front of the rear wheels pictured below) on my 2006 997 coupe . The part traps dirt and moisture.
I wanted to ask the forum if it it a aerodynamic part needed for car stability or rear brake cooling ?
PCA tech told me that it’s purely decorative.
I wrote to Porsche USA - they told me to ask my dealer -my tech at my dealership ( excellent dealer) is also unsure- IMO only the factory would have a definitive answer so I have asked Porsche USA 3x to forward my question to Porsche Germany. After I get the rust fixed I will only replace the part if it is functional. I will post a response( hopefully from Porsche) so other 997 owners will know Best to all ! Russ Dejulio Pittsburgh PA



A picture of the replacement part is below
Thank you !
Russell Dejulio
Pittsburgh PA

 

I think it's an air flow piece to probably divert air around the wheel and lowered turbulence around the rear wheels, but not sure.

 

Thank you yes that’s what I thought however I checked with PCA Tech and they said the part was purely decorative . I have asked Porsche USA customer help to ask someone in Germany I hope that they can give me a definitive answer . If they serve no function I will remove them .They have trapped a lot of dirt and moisture there causing rust
thank you Best ! Russ

 

See if you can find any wind tunnel testing photos. Would be interesting to see how the air flows around that area which might let us figure out our own answer.

 

Thank you we think alike I looked in the Porsche books that I have and did not see anything I will check online tomorrow I also hope to hear from Porsche USA / Germany w an answer . I will post whatever info I receive . The answer that I received from PCA tech was that it was only a non functional decorative piece of trim
Russ

 

I removed mine to clean behind during some other maintenance last fall. I can confirm this is also an issue on the 997.2 (2009 C2S) the mess collected behind there would have caused rust if I hadn't cleaned it out. The amount of stuff caked in there and it was still moist... The stuff in the lower right was about 1/4 in thick - the stuff around the sensor was dry - that is also covered by the piece.

PSA: remove them and clean behind them before you have an issue with rust. I've added this to my pre-season clean-up process.

 

I definitely will thank you if I replace them Best ! Russ

 

Wow. Life in the rust belt I guess.

 

You will not get a concrete statement, certainly not that these are decorative parts. But I see the problem and have not yet checked with me. Can the parts be mounted with more distance so that they are ventilated and the dirt is flushed out?

 

They are aerodynamic part to prevent air to flow directly to tire and create drag (and often lift too). Almost all manufacturers have these in front of tire on all 4 corners, some just plastic flap mounted to body or part of wheel splash guard extension and some style it (like in 997).

Auto manufacturers never/rarely put parts like these (underbody parts) without any function as we are all under cost, weight, fuel consumption and emission pressure. How do I know this? I work for a major Auto maker in Aero/Thermal Computation Fluid Dynamics area. From my estimate these parts usually worth 0.002 or more with wider rear hip/tire in aero coefficient of drag reduction.

 

My car is at the dealer now for service after that I am going to ask to be referred to a body shop they recommend so I can ask them thank you for your suggestion. I also wrote to Porsche Germany someone involved w the museum there and asked if he could answer my question or refer me to someone who could . This designer worked on the 997 so if he responds I should get a definitive answer achim.stejskal@porsche.de I will leave info on Rennlist. Frankly I am very disappointed none of my friends in PCA here even those with 4 Wheel Drive 911‘s have had any rust and I don’t drive my car in the snow or salt !!

 

Thank you ! So after I get the Rust fixed I will reinstall the part I appreciate your thoughtful response Russ

 

yes it’s unfortunate and I don’t drive my car in the snow or salt

 

same.

 

I wanted to close this out with the answers I received in regard to this parts function on a 997 .

I received answers from PCA Tech Excellence magazine tech and my local Porsche dealer Service Manager.

The trim serves no Aerodynamic function It is mainly decorative and protects the car body from rocks picked up by the rear tires

My dealer is going to replace the trim because they told me that rust was on the part ( I assume screws clips that hold it on ) but luckily not the body of my car .
Thank you for everyone’s input !
Best !
Russ Dejulio
Pittsburgh PA