APR GTC200 Setting
 

Anyone running the GTC-200 wing? Installed mine and have it at the lowest setting, the base plate is obviously tilted (due to trunk design) and am wondering if the wing angle needs to be adjusted and if so how much. On my previous cars, I'd get baseline from the known race company (Bimmerworld) taking the guesswork out but would appreciate if folks running it can chime in on the height they have tested and their findings.

TIA

Lutfy

I'm no aero pro and have no first-hand experience with it. That said, you probably want to share more information like other aero modifications, suspension setup, tires, etc. I see from your signature you're competing in time trials, so that is helpful.

550/550lbs Motion Control Suspension (MCS) double adjustables, TRD swaybars, ride will be set to 13 -13.25 inches hub to fender f/r, 255 R888 with 17*9 wheels. APR non adjustable front splitter. Weight 2700lbs without driver.

Cheers,

Lutfy

Very similar setup to mine, except my suspension is slightly softer (around 340/450 F/R) and I have a bit more rake (about 1/2 in), same size wheels with 245 RS4 tires and same front splitter and wing. My car is NA and on stock swaybars.

I have played with 3 settings on the wing. Full angle, minimum angle, and middle. I found my car understeered like a pig at full angle, understeered like a smaller pig at medium and had a small understeer at minimum angle. I added hood vents to the car and the aero balance changed, now its slighly loose at minimum angle (very very small, its almost all neutral) with the dampers being set softer in front than rear, and its about neutral with a hint of understeer if dampers set harder on front.

Regarding speed traps (from videos and just eyeballing the speedo before braking on straights), my top speed drops by around 5-8mph on a 100+mph straight from maximum angle, to minimum angle.

Regarding lap times, Im around 1sec per minute faster with the wing at minimum angle vs maximum angle.

Middle angle was like maximum, but less. Meaning less drop in lap times, less drop in speed, less understeer, but still worse than at minimum angle.

Hope this helps.

Awesome info! I intend to realign to -2.8/9 front and likely static -2.2 (stock arms).... My fear when looking at the wing was that the angle looked a bit reversed (from the middle) giving me fear of having lift (reverse tilt) but your feedback allows me to go and test it out. If you can share any pics, that would be great!! So so many variables (converted from TTE to TTD overnight) I have one test weekend before timed event so want to make sure I have all the notes/data/documentation prior.

Cheers,

Lutfy

I get what you mean, indeed the wing looks like it has negative angle (and it does!) but it is still generating downforce at negative angle, and according to APR themselfs, the wing is most efficient at -2 angle of attack (which is around what the minimum angle is). I forgot to mention camber, I run a retarded amount of camber, -3.8 in the front, -3.2 in the rear. I started increasing it from -3 front and -2 back until my current setup, every time I added more camber, I went around the track faster... At -3.8 I think the front still needs a bit more, at -3.2 I think the rear needs a bit less, Im going to try -4.0 front and -3.0 rear next, see how that works out. I have -0.1 toe (toe-out) front, and 0 toe rear.

Amazing info thanks mate!! The wing angle is one less worry. Got all the baseline I need to hit the ground running!!

Lutfy


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Bringing up an old thread. Have you measured the AOA at full min to see its actually -2? I ended up getting a shorter height link from APR to see if I can actually go lower. With 3d wings you still have df and drag at - AOA so I may go down to as much as -4 if possible.

Am losing a LOT of speeds in the straight and seriously contemplating going with the 2d GT250 wing.

Lutfy

I have the same problem as you with speed Lutfy. I put the wing at -2 and there certainly is enough room to go down more. I will be at a high speed track this next tuesday so I will try 0, -2, and however much lower I can go and collect some data. You can totally tell the différence between say +5 and -2, the rear is completely different, specially during trail braking. I have gotten better at that so I think I will be faster with a lower drag, lower DF setup. I will try to come back here and post some data if I remember. Maybe quote me or msg me if not, I always check alerts on the forum.

Thank God I am not the only one :) I got shorter height adjusters from APR. They are to be mailed out today. I will measure my current setup (whatever the angle is now at lowest setting) and set the same with the shorter link. I can then go down each degree per session until I find a resolution. I 'think' I can go faster as I have way much DF at the back, car is touch understeery and the drag on the straight hurts speed.

Before moving on to a GT250 I want to exhaust all options first.

Lutfy

PS: @Icecreamtruk perhaps you can also get the shorter links overnighted to you and do the same prior to your tuesday run?

My balanced got quite a bit better after I installed canards. So if you havent done that, its a cheap and effective way of getting more front downforce, but it will cost you extra drag, so to keep that in mind.

Unfortunately canard and diffuser or even vortex gen are illegal in class so I will just have to toodle with the wing. Per your earlier post I did the hood vents and it made a pretty noticeable difference (less high speed understeer).

Lutfy

What do you expect to be different with the 250 wing?

[QUOTE=Sleepless;3128564]What do you expect to be different with the 250 wing?[/QUOTE

Less drag especially at higher speeds. More efficient wing.

Ordered a set of shorter rods and will go down to as low as -4 degree to balance and also gain some mph at VIR.

Lutfy

Less drag, with less downforce. Are you out of options to increase front downforce and/or ways to make the rear looser?

I use a much, much larger wing than your GTC200, with a higher mount, without balance issues.

This is not how I understand canards to work. My understanding is that drag reduction is their main purpose by causing the air flow to be smoother around the front wheels. I'm pretty sure you'd needs some seriously massive canards to actually generate any downforce.

Mike, what is your current aero setup (parts only; not asking for secret tuning sauce :) )

Thx

It depends on the specific placement and design of the canard. Some can make front downforce, a different placement/design can reduce drag, and yet others can shape airflow around the car to increase rear wing efficiency. There are other effects/uses as well, but these are the most common.

APR front lip, Trackspec hood louvers, and Voltex wing (Type 1S, 2, and 12 in rotation at the moment).

Remember there is both static and dynamic balance involved, in getting the cornering behavior you want out of a car. When one limits you, you can use the other to (somewhat) compensate/balance.

Mike logical step is to run down (negative AOA). Currently at -1 at full low (rod setting) and APR sent me a new shorter rod so will try -3 and ultimately -4. There is still DF at negative AOA given the 3d curve.

Lutfy

There is still downforce at negative AOA, because your AOA measurement is relative to the ground, and not the plane of the airflow over/around the car, hitting your wing.

Thank you very much for posting this helpful thread.
Like you, I was missing a few MPH at the end of most tracks when comparing to before Aero BRZ in my case. Awesome on the shorty and twisty ones. After reading your thread, I have no doubt what was causing the drag. I was running 6 degrees positive AOA at the center :confused0068:
Really out of ignorance more than anything and basing myself in the curves I saw in the internet.
I am going to shorten the eyelets myself and go to -2 degrees AOA at the center of the wing to start with. That should suffice.
For the record, the two eyelets when threaded into the rod are too long to bottom out inside the rod and you will not get them any closer with the potential to break them. I plan to shorten all eyelet threads at least 1/4" on each end so it should give me what I need for down to -4 AOA at the center and to avoid contact between them.
Please keep us posted with your results on the different AOA at the center of it and your impression on downforce and drag.
I do have the canards and the APR front splitter along with the APR rear spats and the FT86 aggressive rear diffuser with differential covers.
Like you, I have contemplated to swap this wing for the GT250 which I know produces less drag cause I have driven on it on my buddy's BRZ but it is much more $$ and I am on a tight budget.
On the other hand, I had talked to the guys from GoodAero and I wish I had the budget to really invest with them. They are awesome and very thorough but unfortunately, cannot afford it.

6 degrees is too much. You can eliminate the screws sandwiched between the eye bolt and the rod for more clearance. Mine would collapse all way without touching. I got shorter rods from APR and restarting from 0 AOA and going down from there.

I realized no need to get rid of the wing just find a way to adjust.

Will update with new settings soon.

Lutfy

To get back to this, I ran the wing at around 1 degree last weekend at Circuit Mont-Tremblant (high speed track, old Canadian F1 layout). The car is looser in high speed sections but not by as much as I had initially though. I gained some 3mph or so down the straight, so not huge, but car balance was way better. Comparing times to a different day with higher wing settings, newer tires, colder temps, I should have been a second slower or so, but was instead able to get within 0.1s of my best time there, so it did help I think.

I also had an offtrack excursion at 110mph, so now Im rebuilding my splitter (the rest can be left to imagination). Im going for a bigger and more robust splitter this time, trying to add front downforce instead of removing more from the rear.

Thanks for sharing and sorry about the mishap :(

When you got it down to 1 degree, was your current rod height set to full low? Mine was maxxed out (low end) before I got shorter rods. Do you know your previous setting (angle) prior?

Even at fully maxxed out (low), I was facing touch of high speed understeer but rear end stability was very confidence inspiring. I could put the power down (was limited by LSD until I got that fixed) much earlier. BUT it was costing me some speed....

Lutfy

It was around 5 degrees earlier (calculated from hand taken measurements), the rods can go down a bit more, probably 1 more degree or 2, but not much more. At very high speeds (well, for this kind of power at least), the car still had a touch of understeer as well but it was rotating well for most of the track. I dont think it cost me much time to be honest, I was actually gaining time vs everyone else on those sections, but was loosing time in the slowest sections of the track, during turn-in mostly, which points towards something else so I think at this angle the balance was about right for me (I do have the canards and you dont, so you probably do want less angle than me).

If its at the slowest part of the track, then you want to tinker with your suspension.

FWIW, I am running -3.2 front, -2.6~ rear with zero toe. I had 550/550lbs square but had to get 650lbs rear to get rid of the nasty push. Now the car is balanced (mostly and very well indeed with a touch of understeer), I was trying to gradually reduce aero (back) to gain some time and experiment.

I'll have to admit, the LSD made a fair bit of difference in my car. I had to go from almost full stiff (compression) at the back to middle setting. In the past I was using shock as a bandaid to balance but thats not the issue now.

Lutfy

Remember that a splitter that is too strong will just pass in the force to other things. I prefer splitters designed to be "just enough", so that if something needs to break away or fail, to prevent other damage, the splitter goes, rather than something else.

Yeah, thats what I had in mind as well. So this next splitter will be designed to be strong resisting force downwards but to relatively easily brake away from the rest of the car if it catches something solid like a big bump or an offtrack excursion. Lesson learned the hard way this time I suppose.

By the way, Im thinking of getting a clutch type LSD for next year Mike, I will contact you for that as that is something I have little to no experience with so I will have to rely on your expeertise for the setup.

For the setup Lutfy, I think I understand more or less where my problem lies now (sadly, after the championship is over). But it is indeed a mix of suspension and aero imbalances. Trying to fix it all now and test before tracks close for the winter, as there is usually very little time to test in spring before the championship starts again.

It’s a never ending journey so worry not :) try to keep all other variables constant (especially the tires). I had a long convo with KC from APR who shined a bit of light to get the aero tuned. I have some variables to test (less angle) but this weekend is not looking promising.

Start at the 55 sec mark and you’ll know what I mean by aero drag: https://youtu.be/d--eoaLaAD4




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The shorter rod/link worked and got us closer to -2 degree AOA. Overall the grip was there there, some slow/mid speed trackout, there was a touch of oversteer. Dialed it out with softening the compression (one click) at the back and increasing rebound (one click) in the front. Just a touch to balance things out.

Bottom line, the drag was reduced.... In past I had the RX8 I have been competing with pull hard on me, but now it was just a touch but was able to gain on him in higher speed corners mitigating the drag by increased downforce.

Lost by a 10th of a second at Dominion in class but thats a different topic :) Next outing, Watkins Glen.

Lutfy

Alternation options is to run a higher setting on the rear sway, or increase rear tire pressure slightly, to run optimal damper settings.

Mike tried stiffer bar at the back. Car was a handful. With my spring rates, the stock bars work better.

Increasing rear pressure would only lead to less grip (running 36 hot as is on R7). This is for exit oversteer.

Lutfy

Ah, specifically exit oversteer.

Do you have a clutch type LSD?

Yes I do. OS Giken 1.5w, build based on mods/current specs (after filling out their sheet).

Lutfy

How is corner entry/mid behavior?

is the rear looseness specific to exit, or does it coincide with throttle application?

Stable at entry/mid corner its throttle induced. I will have to put a video up to show throttle/steering input.

Could be the tires (20+HC on them now).

Lutfy