AlpineFD

Looking to get my 981 setup to be more capable at the track. Have been doing this for quite a while but first time in a Porsche !

I have 981 GTS with X73 suspension

tire are DOT R-compound tires like NT01 and in the future Advan A052 (street tire but extremely grippy faster than nt01) etc.

so far tried a maxed out alignment without changing any parts.
front camber -1.7, rear camber -2.2
front toe 0, rear 1/8 total toe in
it's ok but not quite happy with the overall performance

next step i'm looking to do is change the suspension arm to get front -3deg camber, and rear -2.8deg camber

it seems the proper setup is front/rear GT3 LCA (thinking tarett gt3), with solid inboard bushing, and solid thrust arm bushing.
change rear toe link to a spherical bearing toe link.

i have 4 questions
1. should i change the thrust arm front and rear as well? with my planned setup, i'll have solid bushing in all locations except the front thrust arm bushing (chassis side)
2. with the LCA, should i use solid thrust arm bushing in front and rear, or just rear? what's the pro and con of adjustable vs non adjustable thrust arm bushing (control arm side)
3. is there an optimal caster setting? it seems changing the LCA like this would affect the caster quite abit, should i just get adjustable thrust arm bushing (control arm side) to adjust caster back in the 9-10deg range? How should i optimize the thrust arm vs control arm interaction?
It seems to me there is more to it then just setting the caster and then the camber. or is it really just that simple?
4. i see Manthey racing in their GT4 track package also included a replacement inner tie rod. Is this necessary?

khoahtran

With the lca you would need extended front toe links, since the oem doesn’t have enough thread engagement once you shun the lca out.

i would get the rear toe link from tpc to correct the rear toe curve. You don’t absolutely need it because you won’t be lowering the car but it helps the wiggle under braking.

Fronts need the adjustable caster bushings, rears don’t need the adjustable. With the front adjustable bushings you won’t need the thrust arms. I’m tried both 9 and 10 degrees and have gone back to 9.

camber, caster, toe is basically all you’re adjusting. The solid pieces you’re installing is just deflecting less...since you’re still on x73 i wouldn’t go too crazy... LCA and front tie rods would be my first step, the camber will make a huge difference.

AlpineFD

thanks for the info ! Nice to have confirmation the front tie rod is needed.

it seems if you had an adjustable LCA, aftermarket camber plate option, plus an adjustable thrust arm, you could have multiple setting with the same alignment setting but with different suspension geometry and different wheel base and track width.
am i overthinking this?

khoahtran

Yes you can have same alignments with different geometry. I have both camber plates and extended gt3 lower control arms. With my camber plates push all the way in, I can get -3 with stock lca. with the extended lca, I can get -2.5 without adjusting the camber plates. With both the plates and lca i can get -4.5...right now I have -3 with lca and the camber plates pushed in a tiny bit, this gives me the camber plus 15mm wider track on each side. The wider track makes a huge difference.

AlpineFD

so i purchased a full set of RSS control arm and tie rod ends toe links etc.
got the XL version to get to the -3 front camber target easier.

now thinking about it abit more, i'm wondering if the stock shock top hat on the X73 suspension will be able to handle the -3 camber?
i'm assuming it's just a rubber top hat? is it asking too much for it to rotate that much with the longer lower control arm to get the -3 camber?

khoahtran

No issues with x73 and a wider track, I have a buddy with the same rss xl lca and x73 w -3 and no issues.

AlpineFD

perfect ! Looking forward to get the setup on the car.

Now, the RSS lca have shims that can shim the outer ball joint it up and down, it seems to me this will affect the camber curve.
When the car is loaded on the ground, if the outer ball joint is pointing down relative to the lca inner bushing, then as the corner goes in bump direction, the outer balljoint would scribe a arc that's gains negative camber (ball joint goes out wider).
is this the right way to decide where to space the outer ball joint of the lower control arm?

maybe i should just measure the factory lca carefully to have the ball joint of the RSS lca in the same spot, but it's difficult to find the true pivot center of the ball joint