Best Front Splitter To Match APR GT250

[former 240 s14]

Hey track rats!

I maybe upgrading my aero and getting a second hand GT250. It's a lot of wing and I was wondering what the right reco from the Aero experts in the forums would suggest I go with to balance the rear?

Thanks and ask questions! Currently I have a GT4 Front lip as I am using the brake ports for cooling.

Rubin

[omgzirra_exe]

Tough question honestly. Most people will default to Zebulon because their front aero is designed to match their rear wing, and the GT250 should be in a similar ballpark aerodynamically – maybe a bit lower, but not wildly different.

If you don’t want to jump straight into a full, aggressive splitter setup, I’d look at GT4 canards or AJ Hartmann canards first. They add meaningful front balance without forcing you into a huge splitter right away.

If you decide to build your own splitter, starting around 4 inches of extension is a solid baseline. Then just test and tune from there to see how the car responds.

[kolosy]

Originally Posted by omgzirra_exe

Tough question honestly. Most people will default to Zebulon because their front aero is designed to match their rear wing, and the GT250 should be in a similar ballpark aerodynamically – maybe a bit lower, but not wildly different.

If you don’t want to jump straight into a full, aggressive splitter setup, I’d look at GT4 canards or AJ Hartmann canards first. They add meaningful front balance without forcing you into a huge splitter right away.

If you decide to build your own splitter, starting around 4 inches of extension is a solid baseline. Then just test and tune from there to see how the car responds.

I was reading that you want 2x the ground clearance for your splitter if you’re going the Home Depot racing route..
I will say that my gt4 lip and canards were woefully inadequate for my (admittedly massive) 72” swan neck.

[F4rmost]

I quite literally just got a 67" GT250 used so good timing former 240 s14 LOL

I just bought a v1 GT4 splitter, and am thinking of getting some canards, and omgzirra_exe just confirmed it.

[omgzirra_exe]

Originally Posted by kolosy

I was reading that you want 2x the ground clearance for your splitter if you’re going the Home Depot racing route..
I will say that my gt4 lip and canards were woefully inadequate for my (admittedly massive) 72” swan neck.

If you’re going the Home Depot splitter route, ground clearance is not the real issue. The real problem is how the material handles heat and aerodynamic load. Once you get above 120 mph, plywood starts to flex, buckle, and eventually warp from the pressure and heat. To keep it stable, you need to brace the splitter with a proper frame using square tubing or similar support. Splitter rods alone will not keep the whole surface flat or prevent flex.

You should also round off the leading edge of the splitter. A smooth radius helps reduce airflow separation at the front, keeps the air under the car cleaner, and improves how the underbody and rear aero work together. This makes the whole setup more predictable and efficient.

[kolosy]

Originally Posted by omgzirra_exe

If you’re going the Home Depot splitter route, ground clearance is not the real issue. The real problem is how the material handles heat and aerodynamic load. Once you get above 120 mph, plywood starts to flex, buckle, and eventually warp from the pressure and heat. To keep it stable, you need to brace the splitter with a proper frame using square tubing or similar support. Splitter rods alone will not keep the whole surface flat or prevent flex.

You should also round off the leading edge of the splitter. A smooth radius helps reduce airflow separation at the front, keeps the air under the car cleaner, and improves how the underbody and rear aero work together. This makes the whole setup more predictable and efficient.

My bad, I wasn’t referring to the splitter needing ground clearance, but rather that the length of the splitter should be 2x the car’s ground clearance.

What you’re saying makes sense also. I was going to run a plywood one for a bit and then get a cf sheet cut.

[omgzirra_exe]

Originally Posted by kolosy

My bad, I wasn’t referring to the splitter needing ground clearance, but rather that the length of the splitter should be 2x the car’s ground clearance.

What you’re saying makes sense also. I was going to run a plywood one for a bit and then get a cf sheet cut.

oh yeah front to back length yes, but if you were to build one for specific race classes, I think 4in from the front bumper is like the starting point?

[dogbone]

I think it’s fair to say I’ve been down the road of aero on our platform. My first full setup was a 67” APR wing paired in the front with a generic front lip to fill the space between the bumper and an APR composite (the cheaper stuff, not the expensive honeycomb) splitter. Racewerkz Engineering designed the shape of the splitter for APR and installed it. That setup also had AJ Hartmann canards and hood vents and top-of-the-wheelwell vents. That setup worked well. The car was fast. But you could not easily tune the splitter. And it was not chassis mounted. And it was always in quite a bit of danger of being ripped off during an off-track excursion (gasp! Do those happen?) But still fast!

Over the course of many years, the APR splitter got sort of saggy a bit. It had seen a lot of action. It was rubbing the ground and grinding away into oblivion. I don’t blame it. It’s a thin composite sheet. I definitely got good value out of it. If you’re on a tighter budget, I think it’s a very viable way to go.

But then Zebulon hit the scene on our platform thanks to the efforts of Ryan@Zebulon and Chris Mayfield (fsmtnbiker). The Zebulon splitter is simply in a whole other category—chassis mounted, easily tunable angle of attack, hidden gas shock front support rods that give the splitter the ability move upwards if it slaps the ground, super stiff carbon fiber—you can LITERALLY stand on it when it’s on the car, and every one is custom built so you can choose exactly how far out it sticks from the front bumper, if you have a class restriction. But it’s more expensive than the APR. And it’s more work to deal with building an air dam to fill the gap between the bumper and splitter.

Ryan from Zebulon told me awhile back that pretty much any splitter in the front will help quite a bit with guiding air over the car versus allowing the air under it, and that it’s diminishing returns by switching to another splitter in terms of just sheer downforce. So he warned me that when switching from the APR to Zebulon, it would not necessarily be night and day difference, but, yes, it would be more downforce and I would have far more tuning options to create the aero balance I wanted.

Now, as far as canards——they are NOT creating any big downforce. I still have them and it takes very little downward pressure to make them flex. The point of the canard is to SHAPE the airflow over the front wheels. After my VIR crash, I had to replace the bumper and start over. Amazingly, the splitter was able to be repaired after going straight into a tire wall. And Ryan from Zebulon helped me relocate the AJ Hartmann canards to a spot on the bumper where they could more effectively guide the air OVER the front wheel well arch. I originally had them lower, and he recommended putting the upper ones as high as possible given the M3 bumper. So, if you look at old bumper vs new bumper pix of my car, you can see the top set of canards are quite a bit higher up than they were on the old setup. Basically, the front wheel well is a turbulent mess. Without any mods on a street car, air gets in there and the wheel is spinning and the air gets trapped and it becomes a high pressure area which is the last thing you want. So, vents allow pressure to escape, and the canards flow air away from the wheelwells in the first place.

Hood vents are also for pressure release to prevent air pressure from building up underneath the hood, and for air flow. Some car magazine actually put an M3 in a wind tunnel and calculated that a stock M3 at 120mph generated 20lbs of uplift just from air pressure under the hood. The hood vents also encourage airflow through the engine bay that may make it more efficient for air go through the radiators, which helps with cooling.

Canards, wheelwell vents, hood vents——none of these things have a large effect on the car by themselves, BUT there is no doubt that together, as a system along with the splitter, that they give the car incredible amounts of front grip when setup properly.

Below, you can see the new canard setup versus the old setup. The canards were so flexy, that I connected them with a metal strap just to try to give them the chance of flexing less. You can see the strap in the bottom photo connecting them.

New:


Old:

[omgzirra_exe]

Originally Posted by dogbone

Now, as far as canards——they are NOT creating any big downforce. I still have them and it takes very little downward pressure to make them flex.

I totally forgot about that when I mentioned them. No idea why AJ makes them so thin, but they definitely need some reinforcement if you want them to do anything.

Same deal with the GT4-style canards. The cheaper ones flex also.

[former 240 s14]

Well my current GT4 lip was curving up (its old and not idea about its entire history) so I just ordered a new GT4 lip from SPECRING for $377 shipped. For that price had to try it and it can't be anyworse than what I have now. Already have the canards but will upgrade them next offseason. This engine rebuild is bankrupting me so trying to be mindful of what else I spend.

Thanks everyone!

Rubin