By the way guys, I'm really enjoying this conversation! I've actually learned a good deal of things looking up the stuff I have posted! I hope you two (NHB, serialk11r) know that!
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Originally Posted by NHB
Vents are there for cooling. More power needs more cooling. I really don't believe that downforce is that important in these machines. I don't have measurement data for CLA, but it's sister model A-Klasse was tested in SportAuto 3/2014. Even with optional AMG Aerodynamics package (AMG rear aerofoil, additional flics in front apron, larger front splitter) it didn't generate any downforce. It generated 430 N lift at the front end and 150 N lift at 200 km/h. Looks are there for sure but downforce is missing totally.
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I can't find an english version of that article, or a site that will translate correctly
But I found this about the A45 AMG, so I find the generation of lift you claim a little bit suspect:
"The car only comes with three options - black wheels ($490), stiffer suspension ($1990) or the AMG aero package which adds front winglets, front wing and a fully sick rear wing which sets it further apart from the A250 Sport but also adds 40kg extra downforce at 250km/h"
(
2013 Mercedes Benz AMG A45 | Top Gear)
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AMG model is the only model which has any change to be decigned downforce in mind.
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I Understand that, but it's not the only one with modifications for aerodynamics.
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Ok. Let's take an example, which doesn't have any aero packages or anything to do with downforce. Here are Cd values for Skoda Octavia:
1,6 l TDI/66 kW 0,286
1,6 l TDI/77 kW 0,288
2,0 l TDI/110 kW 0,297
1,2 l TSI/63 kW 0,294
1,2 l TSI/77 kW 0,290
1,4 l TSI/103 kW 0,301
1,8 l TSI/132 kW 0,304
If I understand correctly, all of these values are listed for standard base model with 195/65 R15 tires. If the tire size wuold increase, we would see a bigger change in Cd.
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Awesome, this is great! I could totally believe that +44kw would lead to .011+ in CD. I could also believe that +69kw would lead to .01+ in CD. Like I said, I understand and believe in the idea...
But take those ratios and apply them to the +175kw of the CLA:
Average the +44 and the +69, use +56.5kw gets us .01+CD.
+175kw = .034+CD
I can totally believe this figure! This would be around 1/3 of the increase in CD for the CLA. But this number would not be the "majority" of the increase in CD.
Lets say the tires account for .025 and the KW increase accounts for .034, that's .059. What causes the other .049 increase in CD
Even if the two combined account for .06 of the .1 increase on the CLA, where does the other .04 come from? It must be aerodynamics of some type right?
~C