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Discussion Starter #1 (Edited)
Anyone else come out an inclined driveway and heard a scrape on the front end, but when you go to find a scrape, you never find it?

Well I was coming out a steep gradient driveway today and just as the front end made contact with the road, PartTronic sent out its signals flares and had its spasms. But I still felt contact. It was pretty loud too. Felt like the front lifted a little. When I went to go check. There wasnt a scrape to be found anywhere on the bumper or underside. But there were there square prong like projections on either side right in front of each tired. They werent bent, but the undersides of them were scraped slightly.

Makes me wonder what those thingamajigs are. And has anyone else experienced this phenomenon?

BTW there is one P is scraping
 

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Yep this happened when we were looking at houses last summer... the house had an inclined driveway and I had my doubts so I took it veeery slowly... heard a scrape and instantly backed away... (deal breaker on the house). No damage. I think the part I hit was a plastic piece behind the center front splitter.
 

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Oh so this is the other scraping post I saw ... anyway might be the serrated tire spoilers that got hit but that doesnt make sense geometrically
 

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Yes there is a vertical piece of protruding plastic hanging off the front plastic shield on each side. I recently also scraped the front end coming out of a Dunkin Donuts parking lot. There were scratches on the underside of the bumper (which I had just has repaired two weeks before *$(#@)#*!!!!).
 

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Discussion Starter #5
Wow @RSM you must have had some incline.

I had a moderate incline and only think I could visibly and tangibly notice to be scratched was those projections pictured here.

20150819_142933.jpg 20150819_142928.jpg
 

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Yup those are the infamous computer optimized aero spoilers for the tires ... so says Benz ?
 

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Yup those are the infamous computer optimized aero spoilers for the tires ... so says Benz ��
What the heck do they spoil?
 

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I had that experience once as well but I couldn't find out where it is scratched........... but I guess it will happen sooner or later anyways :doubt:
 

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Discussion Starter #9
Yup those are the infamous computer optimized aero spoilers for the tires ... so says Benz ��
I think I spoiled it more than it spoiled the air!

After that little driveway fiasco, dont know if they that much optimized anymore. One seems to be bent forward.

On a side note, I now notice that my paint may be what another thread mentioned as orange peel paint.
 

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@Texas Dave - they "spoil" the poor airflow around the tires for better aero dynamics ... well supposedly! ? I saw the airflow patterns and I think the jury is still out
 

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@Spartacus - looked and looked again today just geometrically does not make sense a typical poorly formed entrance or exit driveway would hit the spoilers and not the splitter or front engine shroud ... as the spoiler fingers are so close to the tire ... unless that transverse driveway section has a crown to it but that does not make sense either?
As for the orange peel our CLA paint coats are pretty good compared to other cars' paint surfaces that just beg to be wet sanded. I recall reading somewhere Benz uses PPG paints and there was some R&D into solgel based catalyzed polymers that cure pretty darn close to "glass like" finishes ... but no secrets are open source yet. ?
 

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@Texas Dave - they "spoil" the poor airflow around the tires for better aero dynamics ... well supposedly! ? I saw the airflow patterns and I think the jury is still out
How fast would you have to be going for that to be effective? Man, now we need an expert in fluid dynamics!
 

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Discussion Starter #13
@Spartacus - looked and looked again today just geometrically does not make sense a typical poorly formed entrance or exit driveway would hit the spoilers and not the splitter or front engine shroud ... as the spoiler fingers are so close to the tire ... unless that transverse driveway section has a crown to it but that does not make sense either?
As for the orange peel our CLA paint coats are pretty good compared to other cars' paint surfaces that just beg to be wet sanded. I recall reading somewhere Benz uses PPG paints and there was some R&D into solgel based catalyzed polymers that cure pretty darn close to "glass like" finishes ... but no secrets are open source yet. ��
I may not be vehicle savvy. But can you give me a picture of the area you say may have been scraped. Because I ran my palm a good 6-7 inches from front of the bumper along the bottom. Everything is relatively smooth. Only thing I found to have a rough and uneven edge was the spoiler. Perhaps along with my promised CPA+ experiment for @Texas Dave I'll find out. But on a sunny day I walked a few paces in front of the car and bent over to clearly see the underside of the bumper. It looked okie dokie. Perhaps you may shed light on a conclusion @Clallan have come to add the spoilers being the protectors of the CLA Angelina Julie like lips
 
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Discussion Starter #15
:spank1: (alive enough for you)
 

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:spank1: (alive enough for you)
OK OK ouch!!
So this is coming out of a shopping mall with a poorly graded ingress/egress area but I think
I can touch up and buff this out
RoadScrapes1.JPG
These next two are parking spot concrete barrier cases where either parking too far forward
or the barrier was a tad too high though these I can only smooth out and get rid of the hair
RoadScrapes2.JPG
RoadScrapes3.JPG
And as you can see the serrated spoiler parts are too high and too close to the tire to be dinged
at least in most cases ... unless of course I put the parking spot concrete carrier there instead of
in the middle under the engine shroud
 

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How fast would you have to be going for that to be effective? Man, now we need an expert in fluid dynamics!
Well these are what the flow simulations look like for the serrated spoilers:
(front of car is on the right side of both pix)
CLAwind1.jpg
CLAwind2.jpg
They must have done some sims or trial&error to note they need to be positioned inboard
of tire centerline though without the full FEM spreadsheet we can guess all we want, but at
least this shows some flow evaluation results.
As for at what speed the decision boundaries cross, not sure without reynolds numbers etc
but my guess is since its nonlinear horsepower increase with air resistance, and approximately
we have (presuming Cd~0.28 A~24sqft M~3250lbs) 16hp needed for 60mph and 92hp needed
for 120mph well then I suppose every bit counts above say 40mph? But again that's a guess.
 

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Well these are what the flow simulations look like for the serrated spoilers:
(front of car is on the right side of both pix)
View attachment 20634
View attachment 20635
They must have done some sims or trial&error to note they need to be positioned inboard
of tire centerline though without the full FEM spreadsheet we can guess all we want, but at
least this shows some flow evaluation results.
As for at what speed the decision boundaries cross, not sure without reynolds numbers etc
but my guess is since its nonlinear horsepower increase with air resistance, and approximately
we have (presuming Cd~0.28 A~24sqft M~3250lbs) 16hp needed for 60mph and 92hp needed
for 120mph well then I suppose every bit counts above say 40mph? But again that's a guess.
Fascinating stuff. Never would have guessed that much impact at those speeds. I feel better now, thanks.
 

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OK OK ouch!!
So this is coming out of a shopping mall with a poorly graded ingress/egress area but I think
I can touch up and buff this out
View attachment 20628
These next two are parking spot concrete barrier cases where either parking too far forward
or the barrier was a tad too high though these I can only smooth out and get rid of the hair
View attachment 20629
View attachment 20630
And as you can see the serrated spoiler parts are too high and too close to the tire to be dinged
at least in most cases ... unless of course I put the parking spot concrete carrier there instead of
in the middle under the engine shroud
From here, looks mostly cosmetic, except they aren't really visible. I guess it would be better to say they aren't structural?
 

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I may not be vehicle savvy. But can you give me a picture of the area you say may have been scraped. Because I ran my palm a good 6-7 inches from front of the bumper along the bottom. Everything is relatively smooth. Only thing I found to have a rough and uneven edge was the spoiler. Perhaps along with my promised CPA+ experiment for @Texas Dave I'll find out. But on a sunny day I walked a few paces in front of the car and bent over to clearly see the underside of the bumper. It looked okie dokie. Perhaps you may shed light on a conclusion @Clallan have come to add the spoilers being the protectors of the CLA Angelina Julie like lips
I took a pic but it was badly lit so I'll try describing... just put your hand under the splitter it's less than a hand length away from the very front tip... it's a 3/4" tall piece of plastic pointing straight down and runs all across the front. Mine's lightly scuffed but it's not visible unless you're under the car. If you go up an incline it would be the first thing to hit the pavement rather than the splitter. This wouldn't save you from high concrete parking stops or curbs, you still have to watch for those... just make sure to take steep grades at an angle.
 
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