Churchill

So less than 200 pounds at 190MPH. At 100MPH it's well under half that, i.e. undetectable.

And no, none of this matters, and yes, people should set up their car to look however they want. Just think it's silly when people convince themselves their car handles better taking the highway on-ramp because they've got the wing extended.

Zekiel

I don't know, sometimes you can feel what would seem fairly minor changes. I put a splitter lip on a previous car and the tracking at freeway speeds became just a touch sharper in steering response and stability. Going to a 5 lbs. battery vs. a 35 lbs. one over the nose of the vehicle, I could feel the transient response in turning was more lively in this same vehicle. You could say this might have been placebo effect but I DD this car for more than 11 years so I knew its handling like the back of my hand.

Let's just say, I personally, am not willing to say the rear spoiler is undetectable.

Dennis C

I read a bit about downforce on F1 cars after reading this thread. They produce downforce that exceeds three times the weight of the car. The downforce allows for cornering at 3.5 G. It's pretty amazing.

Hurricane

Very true. Porsche designed them to provide sufficient downforce at the appropriate speed...if you need it, the spoiler will raise on its own.

LnC993

I'm sure 100 lbs of downforce alone would be hardly noticeable. But together with maybe around 100 lbs of uplift the rear wing eliminated, it should make some difference.

StormRune

Yep... just watching that race video posted the other day makes it clear there must be some significant lift at play when there is nothing there. At track speed it seems to have been enough to completely unstick the rear of that cup car.

As Hurricane said, Porsche seems to have gone to considerable trouble to make sure it comes up at the right speed and the right amount. The fact the angle is different for SPASM cars, cabs, and whether or not the top is open must have been due to some good wind tunnel testing to find the right speed and angle for the best results.

Valvefloat991

Sport Auto, the German Sports car magazine does its own aerodynamic tests of various cars. Here are the figures they reported for the 991.2 Carrera S, the 991.1 GT3, and the 991.1 GT3 RS (Positive figures are lift, negative is downforce, at 200 kph (124mph):

911 C2S FRONT/REAR (kg) +8/-8, +18/-18 (lbs)
911 GT3 FRONT/REAR (kg) -18/-29, -40/-64 (lbs)
GT3 RS FRONT/REAR (kg) -50/-94, -110/-207 (lbs)

At top speed, the numbers would be considerable greater:

911 C2S (190 mph) F/R (kg) +19/-19, +41/-41 (lbs)
911 GT3 (196 mph) F/R (kg) -45/-72, -98/-157 (lbs)
GT3 RS (193 mph) F/R (kg) -121/-228, -267/-502 (lbs)

In all cases there is more downforce in the rear than in the front, which tends to favor high-speed understeer, exactly what you want for stability. And you can see why the GT3 RS corners so well. At top speed the aerodynamic downforce increases the vertical force on the tires by about 25 percent.

This is relevant even on the C2S, where the overall downforce is zero, but the front/rear balance favors stability.

gearFX

Great post! I can't read German, and don't have a subscription to Sport Auto, but do they publish similar test data for all Porsche models? (I tried looking for a comprehensive list, but couldn't find one.)

Valvefloat991

Sport Auto is a monthly and, in each issue, it runs one "Supertest" that has all of this detailed information, along with lap times they generate at the Ring and Hockenheim. Being a German magazine, they take great interest in Porsche's but don't necessarily subject each model to this procedure.