APR GT-250 vs GTC-300 Wing

[72dan]

This is the car I ran some races in last year and running this year. Have a couple sprint races this weekend. The wing does look more like the GT-250 wing.
It is placed lower but this is a tube frame car no front side windows just window nets and no rear window so we get some airflow through the car as well as over the car. In the pit stop I just got out, the crew is refueling right through where the rear window would go. The wing isn't chassis mounted but part of the full rear section, you can see in the photos just a few quick release latches and the entire rear bodywork comes off in one piece.
The car only weighs about 1550 lbs. so a few hundred lbs of downforce is a bigger percentage.
It does make a big difference on high speed turns, they have a school car with just a lip spoiler. The wing makes it possible to take turn 8 at Big Willow flat out in 6th gear. The car is only 230 HP so it is maybe 125-130 mph. The car has full aero, vented front fenders, front splitter but you can't stand on the splitter, rear diffuser.
It has a 2 liter Renault motor, six speed Sadev trans with paddle shifters, clutch is only to pull out of the pit then no lift upshift. Solid rear axle, we do run a diff cooler with a pump. With a solid axle hitting the inner apex does upset the outside loaded tire.

[roastbeef]

Originally Posted by lutfy

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

so, what i'm interpreting what you're saying is- you were able to keep your corner speed up that your overall speed in the straight was higher as a result, thus negating the drag the wing caused?
seems like there are no downsides then... as long as you find that healthy medium.

[72dan]

Originally Posted by roastbeef

so, what i'm interpreting what you're saying is- you were able to keep your corner speed up that your overall speed in the straight was higher as a result, thus negating the drag the wing caused?
seems like there are no downsides then... as long as you find that healthy medium.

The other benefit of a wing, it allows you to brake harder. One of my frustrations with my E92 is it has too much front brake bias and there is no way to adjust it. In the race car I have a proportioning valve in the cockpit that I adjust during the race. Sometimes the front tires get greasy, too hot so more rear bias and also with a full tank of gas. Near the end of a stint tank is low 1/2 turn on the dial towards front brakes.

With a lot of aero and a race car with no ABS or power brakes, we stomp the brake pedal as hard as we can at 100 mph+, really hard to lock the brakes with a lot of downforce, then reduce pressure as the car slows and we lose downforce so we don't lock a tire. Delaying braking is huge because the car is going the fastest, traveling the most distance in the least amount of time.

I wonder if anyone here as switched to Motec electronics and management and if it can be done on a street car. The newer GT4 cars all have adjustable ABS and traction and stability control. I find that M mode is too conservative on traction and stability control especially now with the SPL arms and AST coilovers and it would be nice to be able to adjust brake bias. Cars from the factory tend to have too much front brake to avoid lawsuits where the car spins under braking, but for a racing driver more rear brake can drastically shorten braking distance.
Have you ever come off track and put a thermal heat gun on your brake rotors/calipers? My fronts are maybe 450-500 degrees, backs are barely over 200 degrees.
My first Toyota Tunrda year 2000 by 50K miles I had gone through three sets of front brake pads and warped two sets of rotors, rears were drum looked brand new. Found an adjustable rear valve based on rear ride height, if the bed had 600 lbs of load the rear was 2" lower so more rear brake bias. Adjusted that and the next set of front brake pads were still good at 100K miles stopped much better, fronts didn't overheat anymore.

So long winded response, a big rear wing and more rear brakes would lower lap times.

[macdude357]

Originally Posted by 72dan

The other benefit of a wing, it allows you to brake harder. One of my frustrations with my E92 is it has too much front brake bias and there is no way to adjust it.

Couldn't you tune brake bias a bit by using pads with higher friction co-efficient on the rear compared to the fronts (like using CarboTech XP10 on the front and XP12's on the rear)? Wouldn't give you the ability to adjust on the fly though.

[72dan]

Originally Posted by macdude357

Couldn't you tune brake bias a bit by using pads with higher friction co-efficient on the rear compared to the fronts (like using CarboTech XP10 on the front and XP12's on the rear)? Wouldn't give you the ability to adjust on the fly though.

It is one way to do it and some racers use different pads front and rear but as the brakes heat and cool each pad has a different curve for coefficient of friction.
Since the backs don’t get nearly as hot as th front maybe a pad that will take less overall heat but has higher friction at cooler temps.

Another way to do it would be to put larger pistons in the rear calipers, same pressure over more area is more clamping force.

I am running StopTech Trophy brakes 6 piston front 4 piston rear. Didn’t ask when I bought them if there was an option for different piston sizes.
I use Pagid RS29 on track and StopTech semi metallic pads on the street. There may be better street pads than what StopTech makes I haven’t tried others.
I did consider trying different race pads on back with more friction. Just time and money.
Easier to just have the dial in th car.

[gmx]

Easier and more accurate for sure.
The E46 DSC/ABS has been figured out. You can get off-the-shelf race tested ABS programming for newer stickier tyres inc R comps. Looks like the E9x hasn't yet.

Meanwhile, I've been thinking of switching to Ferodo and trying DSUNO front, DS1.11 in the rear. Not that much difference in the co-efficient curve. The fronts would need a workout to get them working and braking balanced.

[lutfy]

Originally Posted by roastbeef

so, what i'm interpreting what you're saying is- you were able to keep your corner speed up that your overall speed in the straight was higher as a result, thus negating the drag the wing caused?
seems like there are no downsides then... as long as you find that healthy medium.

Hey sorry for the delay. I dont lurk this forum as much as my E90 M3 is now a pristine 100K DD (taking this one to the grave).

I felt the rear wing was generating a little bit too much DF as I could feel it on the straights. Going down to -4 as recommended (lowest you can go per KC at APR) would obviously reduce the drag on the straights, I did not notice a big difference in feel. The wing was doing the job, T10 at VIR or the left hander past the esses was still strong (I can get it to be a touch oversteery) however laptimes were REDUCED. Also because the 3D has a much agressive camber curve so can run - AOA and still create downforce (the sides are still pointing up).

How much was it the wing? Unsure. But I did have the car caged this winter (20lbs lighter than last year) and those are the only two mods.

Hindsight is 20/20 I'd say Id get the flat wing vs 3D but who knows.....

Cheers,

Lutfy

[rhyary]

I am in the process of getting the GT-250 mounted on Hard brackets. I mainly don’t like how the 3D wings look.

I had Ray Phillips write math channels to calculate ABS on/off and I analyzed my LRP data and it shows my rears are going into ABS for longer than the fronts at 120mph and 1081psi on the brakes. I believe the wing will allow the braking to be more evenly distributed.