APR GT-250 vs GTC-300 Wing

[72dan]

I know this has been discussed but I think there is a lot of mis-information. The common consensus here and at APR is that the GT-250 wing works better on an E92 M3.
The assumption is that we are all okay with a 67" wide wing that sits 18" above the trunk lid such that people bang their head on the edge of the wing if you are parked in a public parking lot and someone walks down the aisle between you and the car parked next to you.

The reality is many of us want a wing that is shorter, 61" or even less, maybe even 48" wide and only 6"-12" off the trunk lid because we street drive the car. 48" is about the width of the trunk.

So the nutshell opinion is that the GTC-300 is more "draggy" and that the E92 doesn't have enough horsepower for a wing that "draggy". But the reality is the GTC is a much more efficient wing when you compare the L/D ratio, that is lift vs drag, and we are really looking at negative lift, an airplane wing upside down.

The GTC-300 is already making 151 lbs of downforce at 0 degree angle at 80 mph, whereas the GT-250 is making a fraction of that, 43.8 lbs of downforce. In fact for the GT-250 to make as much downforce as the GTC-300 makes at 0 degrees, we have to run the GT-250 around 13 degrees interpolating stated downforce at 10 and 16 degrees.

Most have said they run their GT-250 at 0-5 degrees, so the reality is that if we hang a 67" GTC-300 18" in the air we just can't get enough front downforce to balance it out. So why not run a GTC-300 that is only 48" wide?

That statement that the GTC-300 is more "draggy" is incorrect. The numbers for it were stated in Newtons, so I put all the data in excel, converted it to lbs and also calculated L/D ratios on it, as APR publishes the numbers in lbs for the GT-250

So, running the GT-250 at 10 degrees would give a L/D ratio of 7.52 , at 16 degrees a L/D ratio of 5.28. Remember higher is better, we want to make the most downforce with the least amount of drag.

So, then lets look at the data for the GTC-300. At 0 degrees and 80 mph the L/D ratio is 8.83, it is a far more efficient wing than the GT-250.

So that is the race car engineering theory, the GTC-300 may actually be better as a more narrow wing lower mounted than the GT-250 full race wing based on much more efficient L/D ratios.
Have any of you tried a smaller GTC-300 wing mounted closer to the trunk surface?

[OG Shark]

Good info. Where are you finding a 48" GTC-300 though?

GTC-200 might be interesting as well - it looks like they might make a SCCA version in 48". Looks like maybe even more efficient and be able to reduce drag down even further if desired than the 300?

[SYT_Shadow]

Seems to make sense to me... it's almost comical to see cars with massive rear wings and nothing or almost nothing up front to balance it out

[Richbot]

Is the GTC300's airfoil more or less tolerant of being down in the weeds of turbulent air though? How clean does the air need to be to get the better efficiency we're talking about? That's where I think you just have to test test test or tunnel tunnel tunnel, there's a whole car doing stuff to the air in front of that wing

The GTC is certainly prettier

I mean, this is pretty much the question the GTS wing and/or later GT4 wings were meant to answer right? It's a compromise solution, better than a park bench parachute for a street car, but not going to give you anywhere near the stick of the giant 61"+ upside down surveillance drones. https://www.m3post.com/forums/showthread.php?t=1165122 seems like looking to a racing series that had some limits on how ridiculous the aero could be if one is wanting to limit the ridiculousness of one's street car's aero wouldn't be such a bad job. I like how he's trying to sell the wing and then posts this pic of the wing not keeping the rear stuck at all:



There's also the itty widdle IMSA wing the E92M's ran: https://www.bimmerworld.com/Body-Aer...D-AM-Wing.html

[lutfy]

I run GTC wing on my low powered FRS with NASA (time trial). From no wing to putting a wing, I gained 1/2 second (all else equal, including having a matching APR splitter up front)

Competitors would pull on me on the straights and I had a long conversation with KC at APR.

Granted, the GT wing is more efficient and you can toodle with the angle of attack to balance. If I had to do it again, I'd get the GT wing.

I changed my AOA to -3 degree (you can run up to -4 AOA because of the 3d shape, there is still downforce due to the camber on the wing) and found it to be a perfect compromise between downforce/drag. Last outing, was able to compare data and not only was the car quicker (laptime), had gained 2mph more on the straight at Summit Point.


Lutfy

[M3 Number 86]

Originally Posted by Richbot

Is the GTC300's airfoil more or less tolerant of being down in the weeds of turbulent air though? How clean does the air need to be to get the better efficiency we're talking about? That's where I think you just have to test test test or tunnel tunnel tunnel, there's a whole car doing stuff to the air in front of that wing

The GTC is certainly prettier

I mean, this is pretty much the question the GTS wing and/or later GT4 wings were meant to answer right? It's a compromise solution, better than a park bench parachute for a street car, but not going to give you anywhere near the stick of the giant 61"+ upside down surveillance drones. https://www.m3post.com/forums/showthread.php?t=1165122 seems like looking to a racing series that had some limits on how ridiculous the aero could be if one is wanting to limit the ridiculousness of one's street car's aero wouldn't be such a bad job. I like how he's trying to sell the wing and then posts this pic of the wing not keeping the rear stuck at all:



There's also the itty widdle IMSA wing the E92M's ran: https://www.bimmerworld.com/Body-Aer...D-AM-Wing.html

couldve been drift day lol

[72dan]

Originally Posted by jktx

Good info. Where are you finding a 48" GTC-300 though?

GTC-200 might be interesting as well - it looks like they might make a SCCA version in 48". Looks like maybe even more efficient and be able to reduce drag down even further if desired than the 300?

Good point I don’t see a 48” one. One further reading the GTC-200:is more efficient than the 300.
On the GT-250 APR said they can make any size. More to it on th GTC.

[72dan]

Originally Posted by Richbot

Is the GTC300's airfoil more or less tolerant of being down in the weeds of turbulent air though? How clean does the air need to be to get the better efficiency we're talking about? That's where I think you just have to test test test or tunnel tunnel tunnel, there's a whole car doing stuff to the air in front of that wing

The GTC is certainly prettier

I mean, this is pretty much the question the GTS wing and/or later GT4 wings were meant to answer right? It's a compromise solution, better than a park bench parachute for a street car, but not going to give you anywhere near the stick of the giant 61"+ upside down surveillance drones. https://www.m3post.com/forums/showthread.php?t=1165122 seems like looking to a racing series that had some limits on how ridiculous the aero could be if one is wanting to limit the ridiculousness of one's street car's aero wouldn't be such a bad job. I like how he's trying to sell the wing and then posts this pic of the wing not keeping the rear stuck at all:



There's also the itty widdle IMSA wing the E92M's ran: https://www.bimmerworld.com/Body-Aer...D-AM-Wing.html

Yeah we need a wind tunnel and a team of aero engineers. All data published is a wing in a clean airstream. So the question becomes how high off the trunk deck do we have to go to get any airflow at all.
And part of the purpose of 61” or 67” wing is that the sides of the wing will see much more flow than the center.

I’ll bet there are enough of us that want a wing that we could get APR to make us a 48” wing that works. If we did a GTC-200 or GTC-300 and put it the same height as the GTS wing.


Sometimes I do wonder if many of the people buying this stuff have any race car tuning ability. If I put on a wing and it made the car push my response isn’t that the wing is too big but that now I can increase rear spring rate, roll bar stiffness or shock low speed compression to transfer the load to the rear tires.

I did a lot of autocross in my 20’s and to get th car neutral at low speed and autocross is really low speed 25-60 mph, usually meant way too much oversteer at high speed. So to me the wing is a tool so I can set the car up with enough rear roll stiffness to be neutral at low speed then have enough wing so the car is neutral at high speed.

I have bumper canards sitting here didn’t work with my front lip need a new lip then want all three, lip, canards and rear wing.

[roastbeef]

Gt4 is pretty spicy

[Azeka1]

Not sure how much it will answer your question, but AjHartman posted this very informative wind tunnel testing video of a 3D Wing (GTC300) versus their 2D foil mounted at similar heights.

[OG Shark]

Originally Posted by Azeka1

Not sure how much it will answer your question, but AjHartman posted this very informative wind tunnel testing video of a 3D Wing (GTC300) versus their 2D foil mounted at similar heights.

Good video but would be curious to see how the 67" compared to their wing as well. Also both with & without the gurney flaps. Someone needs to buy all these wings and do some testing!

[jid2]

Here are a few images I used when I designed the wing on my Evo like 10 years ago. As you mention, even a full height GT wing sees air that has alot of angle of attack. The EVO has a steeper roofline so it's worse than an E92, but I'd guess we are still around 7 degrees.

I would not suggest trying to mix low speed mechanical grip and high speed aero enhanced grip in an unbalanced way. I've had a car with too much rear wing, and not enough aero based front grip/balance and that thing was scary to drive on high speed sweepers. Yes I worked around it for a few tracks days with changes to suspension, but when I fixed the aero and wen tback to a more balanced suspension tune the car was dramatically better and easier to drive.

[Azeka1]

@jid2 makes a good point. Here is some similar wind tunnel data to assist with height placement on the e92 M3.

(A): 2.17 m²
(cd): 0.33
(cd × A): 0.71
at 200km/h
lift front 10kg
lift rear 23kg

[SYT_Shadow]

I find it very entertaining to see boneheaded 'aero' on cars at the track.

As in, stock front end and a massive wing in the back. How is that supposed to improve handling?

I'm completely clear that if I ever do aero I will call a specialist, Bimmerworld, and get a matched front and rear kit

[Richbot]

Even bodged aero setups can make a car faster. It's not always as dumb as it looks. But you really ought to have a splitter/airdam sorted before you get too crazy with wangs. I think a lot of drivers are very uncomfortable with high speed oversteer and choose the stability of a wang and assume the car got faster because the wang makes the car faster and not beacuse the rearward aero balance meant they were more comfortable in 90+mph cornering situations and kept their foot in it instead of lifting. In the end the car has to work for the driver, so I don't totally blame them

ALSO PORSCHE DOES IT SO IT MUST BE GOOD *dons fire suit to drive to grocery store*

[SYT_Shadow]

Originally Posted by Richbot

ALSO PORSCHE DOES IT SO IT MUST BE GOOD *dons fire suit to drive to grocery store*

Oh yes, especially in this forum. All must bow to the Porsche overlords!

[rhyary]

The GTS wing

[Richbot]

Suprised the cD on the GTS is lower but I'm not sure if sportauto uses manufacturer numbers or if they use the wind tunnel to measure

[macdude357]

Originally Posted by Richbot

Suprised the cD on the GTS is lower but I'm not sure if sportauto uses manufacturer numbers or if they use the wind tunnel to measure

Is it just me, or does the GTS have a bit more rake in those photos? Could explain some of the differences in drag and downforce.

[leo95se]

excellent post and thread!
i run a gtc at 0deg AOA with the height pictured above. friends run the 200 with 3-7deg AOA and higher up (equal to roof height) and i would guess i still have more mid corner downforce.
biggest differences to me are ~70+mph corners, where you can truly feel the difference.

there is also significant drag impact. id say 3-5mph on the back straight of wgi, as an example. overall, its still making a difference in lap times.

as stated, when you do add this wing, you definitely need front aero, and more rear compression/spring. i had just a lip spoiler up front and it did nothing. adding canards did the trick.

if i had to choose all over, id likely go with the 200, because i dont think the car benefits from that much standalone downforce. i can see it shining even more with a more aggressive overall setup.

[Pig Farmer]

Originally Posted by macdude357

Is it just me, or does the GTS have a bit more rake in those photos?

Check out the angle of the floor. I think they parked the standard M3 on an incline.

[1MOREMOD]

Bigger is better or because race car.