MarcD147

so far I have not changed my aero settings from stock and I was wondering if any one has done data analysis on impact.

eg back to back laps/sessions with aero stock vs max

• impact on laptimes
• impact on G in high speed corners
• impact on top speeds

interesting areas where the aero could be beneficial to me are WGI the esses; NJMP TB T3 and T12.

a track where I would want stock aero might be Daytona.

will you lose by drag on the straights what you gained in the high speed turns?

if laptime is the same does it create more risk as you run higher speed through corners vs on the straight?

orthojoe

I've never run with stock aero settings, so I can't say. However, the change to the wing is so subtle and the front piece of plastic is so small, I have to guess that the effects are subtle as well. Nothing to back that up though

johnsopa

Remember that the max down force is at top speed -- 220 lbs. at 183 mph. I couldn't find reference to whether the 220 lbs was the "from the factory" aero setting or the max setting. Let's assume it's with the street setting and that the max aero setting is worth 50% more (which I seriously doubt).

So, about 300 lbs at 183 mph. The fastest corners I've typically see on track are 50 - 80 mph turns. I don't remember if lift increases linearly or exponentially with speed. Let's assume its linear which would be the best case.

80 mph is 44% of top speed. That would be about 132 lbs of down force at the high setting vs 97 lbs of down force using the street setting. That's 35 lbs. Then, split that in half for front axle vs rear axle load.

I know I can't tell if 17.5 lbs is added to the frunk and trunk when I'm on the track. Maybe someone else can.

My guess is that we can't tell the difference on most tracks.

I talked with Mike Levitas at TPC a bit about this. He suggested leaving it on the street setting because he felt the additional downforce of the max setting didn't get you anything on the track but did hurt about 1 - 2 MPH at the end of long straights. I had already set my downforce to max and don't feel like undoing it.

MarcD147

@johnsopa
my thinking has reflected what Mike told you but I was looking for data to counter that.... so I am not changing from street till I get info otherwise.


I hope to run with you in a few weeks and that would allow us to compare some data.....

of course there is the Psychological factor as well which could result in more confidence and less lift....

johnsopa

Marc, agreed on all fronts.

I will bet that for most of my track driving (NJMP and Summit Point) I could probably take off the rear wing and it wouldn't make much, if any, difference on lap times. Not sure I want to try it but...

GT3Bob

While I don't have timed data, my experience in fast sweepers - where downforce is desirable - is that the front still gives up before the rear, moving you off line at the limit. A mild breathe off a steady state throttle puts the nose right back where it belongs. Nice, and very easy to manage. A big lift can induce rotation. Fun!

I added 2 degrees of rear wing prior to adding camber (bad idea), and now I am taking it out, back to stock wing setting. Kent at Premier Sportscar Service (shameless plug for a great engineer!) has now gotten the front end to work extremely well, eliminating understeer in almost every situation, but the rear on the GT4 is still the stickiest I've ever driven. It feels like it is velcro'd to the pavement.

Jimmy-D

Let me ask you all this question:

I do spirited drives in my GT4 and there is under-steer and agree the rear is very planted which some times it good. I would like, though, to dial that out a little w/o going crazy. I think the front and rear sway bars(If I am correct) are delivered on Med/Med. What would be the ideal set-up to dial out some under-steer??

4carl

i played with the aero on my first 4 @ the streets. first with just the fronts out,wing down and then with the wing up . The only thing that i felt was 3mph less on the back straight 109vs112. Couldn't feel any difference in balance. liked it better with the wing down and fronts out.

Jimmy, tried all the bar combos i like the front bar mid and rear full hard. Not saying its the best but for me i like it . My alignment is F-1.9 R-1.5 toe F-0 R.131"=21' .carl

arter

Softer on front and harder on back will reduce understeer ( as would more neg camber on front, larger tires on front and lower air pressures on front).

James88

Wouldn't this over steer too easily?

ShakeNBake

I would be really surprised if anyone would notice either a balance or grip difference at canyon or street speeds. This is not high accuracy, it's the data Sport Auto took in their GT4 supertest extrapolated to find the WHF constants of a perfect wing. It's assuming the entire aero effect is coming from a wing (which definitely not, and way more complex), but it should still look like this curve for the most part because the effect is still a V^2 function.



Where I noticed it on my prior car, was in a turn like the 2-3 sweeper and the 16-18 carousel at COTA. Max aero on the 997.2RS made a big difference in V-min and V-max exiting in these corners, and I believe it's very similar in amount/difference between min.max settings on the rear wing vs the GT4. I didn't notice a difference in the other corners at COTA.

ML///

ShakeNbake, you're a data guy. Do you have data for both of those cars on similar performing tires? Not lap times, but similar setup on grip with the car's aero and car being the difference. I think we can view both trace lines to see how the braking and corner speed differ. We don't have to look at just one trace, but layer them and we should be able to see a difference or not as it relates to corner speed. The reason I say corner speed is because most aero should create stability in cornering. We don't have to car about straight line speed deltas. If you have some speed, long ACC, brake and throttle traces we should be able to see something.

ShakeNBake

I do not have back to back and apples to apples vbox data, and a DE adds a lot of variables. My generalization after looking at many laps before and after, but different days, etc, is that at COTA it's worth 0.75 seconds in a .2RS. Now a lot of that is limited to my driving ability and confidence. There are three areas I looked at COTA (on BFG R1). Segment 1-3, 11-12, and 16-19. In 1-3, the stability of the car was much stronger, such that I can stay full throttle (with the normal short shift to 4th, remember .2RS has different gearing) all the way to a small brake before the apex of 3 and then braking into 4. This manifested in a min speed increase of 5mph and exit speed 10mph higher before breathing a bit on the brakes at 3. Again, a lot of this is confidence. I could probably take the risk and dance the car to the same effect without the aero, but there was no more acceleration to get out of the car with the max areo setting, except leaving in 3rd, which is really hard to modulate, and then requires a brief shift to 4th before 3 anyways. The Time gain here is in the neighborhood of 0.3-0.5 seconds.

On the back straight, I lost 3mph top speed due to higher drag. I had a bit more braking stability so I started braking later which negated the lost time, but honestly, I could have taken the same braking point in the other configuration. Again it more of a confidence thing. Going hard on the brakes at 150mph was more confidence inspiring with a more planted rear end - what I would guess a lot of y'all have noticed on the 997 GT cars and even the GT4 to some degree.

For 16-18, I was able to maintain a higher min speed by 3-5 mph and exit about 5 mph faster (115-117mph vs 110-112). That's probably the most dangerous corner at COTA to lose it in, so again, confidence was really what probably drove that delta. It's a corner that you can't really fix once committed, so when the car starts to step out or slides too far across the track in 18, you have to ride it out. With the higher aero, the car responded with an onset of understeer, which is when I knew to ease up a bit, vs. just plain avoiding exploring the ultimate limit with the normal configuration (which was more neutral to oversteer). Time improvement here is 0.3-0.5 seconds.

In the GT4 I went straight to Max cowbell, so no data. I am probably not a strong enough driver in the GT4 to be able to make the min/max aero comparison meaningful anyways. Even the above info from the 997 is more skills limited than a true test.

Bill Lehman

I had posted this earlier on the forum but here's data from Watkins Glen from my 987 Cayman S. The Blue trace is with Getty Wing and Splitter. The Orange is the standard aero. The Blue is faster at the the beginning of segment 2, through segment 4 and 9. The added aero lost 2.4 mph at the end of the back straight.

MarcD147

so bill I am I not good at reading your data let me ask you some questions:

you state that with the aero you lost 2.4 in vmax at the end of the backstraight.
did the aero result in higher vmin in T2 and the Esses?
at what point in the backstraight does the aero result in a slower speed than without aero

if you create a segment that starts at turn in of T2 till middle of busstop what is the difference in segment times?