The question of the place of a rubber overlay to the bumper.
 

Hello, I would like to know which place is best to put on a rubber overlay? In the blue or red spot in the picture?
https://image.ibb.co/fJ5b2w/renault_...9_649_head.jpg

Me i would go blue and wrap around to front of wheel arches. Sure some else with greater knowledge than me will guide you.

which place
 

In Wolf H. Hucho's book,he devoted an area of the text to airdams.He showed all the variants of airdam locations and sizes,and there was nothing intuitive about any of it.
There is a risk that Renault has already optimized the existing nose of your car.
Renault has constructed cars with Cd 0.13 already, and they know a great deal about streamlining.I'd be reluctant to try and second guess them.:p

The one on the picture is 0.35 Cx. The problem is that the rubber pad is not only 90 degrees, but only 120 degrees.

120° as in the bottom is further forward than the top of the air dam, more like the chin splitter on a muscle car than an air dam?
http://ecomodder.com/forum/attachmen...1&d=1512250952

No more like the picture just a little lower angle.. I can not attach a photo because it does not allow me something here. Tomorrow I can take a picture of what the bottom of the bumper looks like.
This is how a rubber strip looks like:
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This straight line from the top is glue.

Seehttp://ecomodder.com/forum/showthrea...rty-35894.html
This was my experience with testing . Will be the best answer. A pic from the front highlighting what the manufacturer did would help. As you said tomarrow.
Most moddern cars use a Spat. A small 1-2 tire with mudd flap looking thing 1-2" vertically angled slightly to the outside 1/3 tire. This softens the angle of impact, and redirects the air to go around the front tire with the smallest protruding wake(hence they stop short of the edge of the tire). This reduces the increases of frontal aera to the smallest number with the maximum effect. At some point the increases in frontal area offset the improved side flow. Theas spats that I have seen (I freek out car sailsmen and start asking them aerodynamic questions wile looking for the patterns of what the new technology is hidden by bodywork) typically start about 2" rear of the red and finish about1.5-2" forward of the finder openings.

Coefficient of drag down, Aera up at equal percentages will net a zero change. Its about finding a balance. And that can only be found by mesuring . To improve accuracy add a vacuum gage so you know if your driving teckneek is consistent or if the results are skued. If posable drive 30mi prior to startingthis test session to insure everything is constantly warmed up.

What are your goals? Downforce (for stability) or lower drag for economy?

An airdam may require other modifications. Porsche found that on their 911, an airdam required a rear spoiler, and vice versa, for best effect. You may want a partial bellypan instead.

How much day-to-day trouble are you willing to put up with? Some people won't accept anything that alters the stock appearance. Problem?

This what my front airdam looks like

View from side