is a GT4 splitter enough?

[kolosy]

I managed to blow up the GT4 splitter on my car and so need a new one. With the car getting gutted and caged this winter I'm not in a hurry to spend $2,500+ on a zebulon setup, but is there something else I should consider between that and the GT4? Or just buy another one for $350 and view it as a consumable?

I'm running a GTS spoiler right now, but will be upgrading that to something more substantial.

[mikerunt]

I would say it depends on how you’d balance the Zeb in the rear. The GTS in the rear doesn’t produce enough downforce. Going Zeb is great if you balance it and have the suspension to support the added downforce.

[kolosy]

yeah, that's what i'm trying to figure out. i know enough about aero to know that i don't know enough about aero. i'm expecting the car to shed 3-400 lbs with everything i'm doing, so I assume I'll need *some* kind of aero, i just want to put off Zebulon for a season if I can get away with it.

I was thinking GT4 in the front and an M235ir wing instead of the GTS one in back like this https://ridgelinemotorsport.com/prod...5ir-style-wing

Or is that still too small to do anything useful?

[mikerunt]

I think that’s a half step personally. Have you done the deep dive of APR’s aero catalog? That could be a good look for the rear as they have a lot of options.

The other component is going to be suspension - unsure what you have for shocks / springs, but reducing weight and then adding downforce could wreck havoc if it’s not a capable setup.

I know it’s a rabbit hole, but if you’re at the point of wanting to increase aero I think looking at the full impact of what adding that means will give a real look at cost. For instance, if you have stock-ish suspension or springs not rated for the downforce of a Zeb + massive rear aero, the benefits of it won’t be felt because you’ll be bottoming out and saving your suspension all the time.

[RalliartRsX]

None of the aftermarket GTS wings do much apart from hard parkers status. There just isn't enough surface aero, wing profile or even wing plates for it to be useful for much else apart from a dinner table for a couple big macs

Look into 9lives, versus, etc and delve into the data they provide and make a decision. Also, if you're class limited, keep that in mind as lower classes have limitations in chord length , surface area and number of elements allowed

Like safety it's a package/balance deal. What are you trying to accomplish? More rear grip? High speed stability? More mid speed front bite? Etc

[kolosy]

Originally Posted by mikerunt

I think that’s a half step personally. Have you done the deep dive of APR’s aero catalog? That could be a good look for the rear as they have a lot of options.

The other component is going to be suspension - unsure what you have for shocks / springs, but reducing weight and then adding downforce could wreck havoc if it’s not a capable setup.

I know it’s a rabbit hole, but if you’re at the point of wanting to increase aero I think looking at the full impact of what adding that means will give a real look at cost. For instance, if you have stock-ish suspension or springs not rated for the downforce of a Zeb + massive rear aero, the benefits of it won’t be felt because you’ll be bottoming out and saving your suspension all the time.

thanks, i'll go digging. i'm running the 3DM/Ohlins dedicated track kit with 685 lb springs in the front and 900 in the rear (he usually does 1000 in the rear but there was some supply issue when i ordered).

[kolosy]

Originally Posted by RalliartRsX

None of the aftermarket GTS wings do much apart from hard parkers status. There just isn't enough surface aero, wing profile or even wing plates for it to be useful for much else apart from a dinner table for a couple big macs

Look into 9lives, versus, etc and delve into the data they provide and make a decision. Also, if you're class limited, keep that in mind as lower classes have limitations in chord length , surface area and number of elements allowed

Like safety it's a package/balance deal. What are you trying to accomplish? More rear grip? High speed stability? More mid speed front bite? Etc

lol @ dinner table for big macs.

good question on what i'm aiming for. it's going to be a brand new car for me with all the changes so i won't have something specific i want to change until i've gotten it together and got some seat time. at this point i just want to make sure i'm not going to make the car undrivable by taking out a bunch of weight (which necessarily will shift the weight distribution forward) and not compensating for it somehow. maybe i'm overthinking it at this point and should just stick on another GT4 splitter (the one on there is unusable and I do have brake ducting running through it) and revisit mid-season.

[RalliartRsX]

So the engine itself is about 480 lbs
The gearbox is center and is either 120 or 200lbs (with cooling, etc) depending on DCT or 6 speed
Rear diff is 100 to 110lbs and located at the rear
The car is pretty balanced judging by my corner weights

And you'd be surprised how much a cage adds so net lose woulbe lower than you think

Also, you're going to corner balance, so unless you're losing 800lbs plus, you are overthinking it and it won't lose 300lbs and magically become a pig.

Key advise; build the base car, seat time, then reevaluate

[RalliartRsX]

Originally Posted by kolosy

thanks, i'll go digging. i'm running the 3DM/Ohlins dedicated track kit with 685 lb springs in the front and 900 in the rear (he usually does 1000 in the rear but there was some supply issue when i ordered).

I'm 10/16 on a non aero car with a custom set of redshift coils

You're going to need more spring rate....even without aero

[RalliartRsX]

Ps if your going up majorly in spring rate, chances are you're going to have to get them revalved

Dampers typically have a +/- 2 or 3 k window you can go up or down in spring rate before you have to revalve

[omgzirra_exe]

a standard combo is GT4 with the bimmerworld rear wing.

you can find data on that set up very easily. so that should give you an idea of what rear wing you can use.

[M3SQRD]

Originally Posted by kolosy

lol @ dinner table for big macs.

good question on what i'm aiming for. it's going to be a brand new car for me with all the changes so i won't have something specific i want to change until i've gotten it together and got some seat time. at this point i just want to make sure i'm not going to make the car undrivable by taking out a bunch of weight (which necessarily will shift the weight distribution forward) and not compensating for it somehow. maybe i'm overthinking it at this point and should just stick on another GT4 splitter (the one on there is unusable and I do have brake ducting running through it) and revisit mid-season.

The car’s center of gravity (CoG) is different from the car’s aerodynamic center of pressure (CoP). Aero is not used to correct/alter the location of the CoG which is located based on the mass distribution of your car. It is a primarily fixed point (does shift slightly with fuel load and with/without driver). Ballast can be used to move the CoG to a more ideal location. CoP is the point on the car where no aerodynamic moments exist but you’ll have vertical (downforce) and lateral (drag) aerodynamic forces acting only at the CoP. Altering wing’s angle of attack (AOA) and effectiveness of the front splitter, the CoP location will shift. For stability, you generally want the CoP to sit behind the CoG. The tire load distributions from the CoG and the CoP are different.

[tsk94]

Depends on the wing. Full sized wing, no. Many here, including myself have run it. The aero balance isn't bad, but not ideal.
GT4 splitter with GTS/GT4/M235iR sized wing, perfect.

If I were to run a full sized wing again, I would want something bigger then the standard GT4 splitter. I'm planning on running GT4 front and rear this time around.

[jmeenach]

I believe Berno runs/ran the Bimmerworld front and rear. I've also seen a lot of people run canards with the GT4 front to help compensate for a larger rear wing than GTS or GT4.

[tsk94]

The BW one is GT4 sized, with no ducts. Otherwise it's essentially GT4.
I ran the GT4 front and the BW Ultralight rear wing, Alex ran the BW GT4 front and the same rear wing.

I don't want to speak directly for him, but we've discussed it and we both felt this combo made the car understeer more then desired in most situations.

[jmeenach]

That makes sense. I've heard the BW lip had more downforce than the GT4, but I have no real world experience with it.

Wonder what aero he'll go with now that the car if fully gutted and caged...