What should I do next to get rid of the "unsettled" rear suspension?

[GrabberBargeCaptain]

This is a daily driver but I drive it in a, shall we say, spirited manner at times. It's all for fun, not a track car. When I go on roadtrips I seek out the twisties. My last 2 cars were a 2013 Scion FR-S and 2017 Mazda Miata so you can see what type of car I gravitate towards.

Mods i've done to my 2023 GT Nite Pony Package (came with 255 Pirelli AS, so i guess it's not 100% a base car with 235s).

FRP track springs
FRP track shocks
Steeda Camber plates
Steeda Rear Camber adjustment kit
Steeda sway bars front and rear
FRP front control arms
FRP shock tower brace, paired with OEM cowl extension (PP1 setup)
PP1 brace (k brace?)
I think that's everything.

Riding on SVE SP1 19x10s, 275/40r19 PS4S square.

Alignment as follows, even on both sides unless specified L and R:
Front Toe: Toe out -0.07 deg.
Front Camber: -2.1 deg.
Caster: -7.1 deg L, -7.0 R

Rear Toe: 0.07 deg L, 0.08 deg R
Rear Camber: -1.6 deg L, -1.5 deg R


The car MOSTLY handles really well, surprisingly well and very solid for such a heavy car, but the new stickier tires really have exaggerated that feeling of the rear being disconnected from the front... it feels like there's a big hinge in the middle of the car and it just takes a second for the rear to catch up with what the front is doing. The front turns in like a motha****** though and feels fantastic. I just want the car to feel a bit more connected front to rear.

I haven't done the FRP rear knuckle to toe link bearings which I am guessing makes a good difference here especially with beefier tires and suspension. I was thinking maybe also i made a mistake spec'ing negative toe in the front which makes the front end dive into a turn but the rear is positive which makes it lag behind slightly? I have seen parts like the Steeda IRS Rear Support Braces which im not sure help with this, or if that's more for wheel hop-i dont really launch the car hard so I dont care about wheelhop tbh. I don't want to go nuts with lockouts etc because I still want the car to be decently comfortable eating roadtrip miles and I dont want to hear it from the wifey when we take my car, so really loud solid mounts etc are no good for me.

Thoughts/suggestions? Let me know if I missed something.

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[17MagMetal]

I have a whole mess of rear end bits.

I vote for two things to kill that feeling:

Toe link bearings - this is a spherical bearing on the knuckle side. This, in theory, minimizes changes in toe as a result of rubber deflecting while driving “spiritedly”. Good alignment angles = good drive feel.

Subframe bushing solution of choice, either brackets, lockouts, bushing replacements, etc.

I have BMRs subframe bracket/lockout kit and the Ford Performance toe bearing, all on Steeda’s progressive lowering springs.

You just need to kill deflection in one way or another to be more “confidence” inspiring.

REAL, REAL NVH came from toe link/LCA bearings. I’d actually do the subframe lockout first to see how you like it.

Anyone saying otherwise is lying. My car is very stupid now so I don’t mind, but if you want to keep everyone happy be weary of any rubber > bearing changes.

 

[shogun32]

it feels like there's a big hinge in the middle of the car

Hey now that's my copyrighted phrase.

Should have started with pinning the IRS. I recommend the whiteline IRS bushings/lockouts and bmr cb005 or the Steeda brace.

 

[GrabberBargeCaptain]

Hey now that's my copyrighted phrase.

Should have started with pinning the IRS. I recommend the whiteline IRS bushings and bmr cb005 or the Steeda brace.

Really? if so you are bang on if i do say so myself

Which steeda brace? I see one marketed for stopping wheelhop.

 

[GrabberBargeCaptain]

I have a whole mess of rear end bits.

I vote for two things to kill that feeling:

Toe link bearings - this is a spherical bearing on the knuckle side. This, in theory, minimizes changes in toe as a result of rubber deflecting while driving “spiritedly”. Good alignment angles = good drive feel.

Subframe bushing solution of choice, either brackets, lockouts, bushing replacements, etc.

I have BMRs subframe bracket/lockout kit and the Ford Performance toe bearing, all on Steeda’s progressive lowering springs.

You just need to kill deflection in one way or another to be more “confidence” inspiring.

REAL, REAL NVH came from toe link/LCA bearings. I’d actually do the subframe lockout first to see how you like it.

Anyone saying otherwise is lying. My car is very stupid now so I don’t mind, but if you want to keep everyone happy be weary of any rubber > bearing changes.

So by the sound of it you are saying the FRP toe link bearing adds that much NVH? That's surprising it adds that much.

 

[17MagMetal]

So by the sound of it you are saying the FRP toe link bearing adds that much NVH? That's surprising it adds that much.

I have both bearings, I would describe the amount of NVH gained with the LCA bearings as greater than the toe bearing.

You are literally taking two rubber bits and essentially erasing them in favor of a direct connection so you’ll get some NVH addition.

Assuming everything else is kept stock, toe bearing additions shouldn’t be very noticeable/painful. I actually think(!) PP cars have it from the factory on the knuckle side.

The rear LCA bearings took the car from “stiff” performance vehicle to holy shit it’s a racecar lol.

 

[shogun32]

Edit: the text below is in relation to adding nvh. The value of the bearings is quite clear and all 3 should be done, IMO


Toe link bearing, no.

The giant lateral arm bearing up front and the big ass rcla bearing in the back, perhaps. But not compared to the isolators for the diff and IRS from both Steeda and bmr which are made of material that is too hard to be perfectly quiet.

Qed, use the whiteline bits.

 

[17MagMetal]

Toe link bearing, no.

The giant lateral arm bearing up front and the big ass rcla bearing in the back, perhaps. But not compared to the isolators for the diff and IRS from both Steeda and bmr which are made of material that is too hard to be perfectly quiet.

Qed, use the whiteline bits.

I appreciated the toe bearing for hard throttle application at low speed. Rear end felt like it didn’t want to wander.

The LCA bearing killed ALL hop during everything. I can let it rip and will have 0 hop no matter what I do.

 

[shogun32]

appreciated the toe bearing for hard throttle application at low speed

Sorry if I was unclear. My comment was with regard to adding nvh, not the value of the various bearings on chassis dynamics.

 

[17MagMetal]

Sorry if I was unclear. My comment was with regard to adding nvh, not the value of the various bearings on chassis dynamics.

Understood, no worries. We’re on the same page!

 

[Dana Pants]

I have replaced or locked out ~16 rear bushings so far and every time I did something the car felt better.

I say go nuts back there.

Also you want a hair front toe in to not kill front tires.

 

[GrayMater22]

Really? if so you are bang on if i do say so myself

Which steeda brace? I see one marketed for stopping wheelhop.

He is 100% correct the steeda IRS brace ties the subframe and chassis together in three different places, there is a significant amount of play between the subframe and chassis. This is where a majority of unstable rear end feel comes from on the s550. I did not lose that unstable feeling until I installed the brace and I have replaced my entire suspension (springs, struts, shocks, camber plates, strut tower brace, etc).

 

[CrazyHippie]

This is a daily driver but I drive it in a, shall we say, spirited manner at times. It's all for fun, not a track car. When I go on roadtrips I seek out the twisties. My last 2 cars were a 2013 Scion FR-S and 2017 Mazda Miata so you can see what type of car I gravitate towards.

Mods i've done to my 2023 GT Nite Pony Package (came with 255 Pirelli AS, so i guess it's not 100% a base car with 235s).

FRP track springs
FRP track shocks
Steeda Camber plates
Steeda Rear Camber adjustment kit
Steeda sway bars front and rear
FRP front control arms
FRP shock tower brace, paired with OEM cowl extension (PP1 setup)
PP1 brace (k brace?)
I think that's everything.

Riding on SVE SP1 19x10s, 275/40r19 PS4S square.

Alignment as follows, even on both sides unless specified L and R:
Front Toe: Toe out -0.07 deg.
Front Camber: -2.1 deg.
Caster: -7.1 deg L, -7.0 R

Rear Toe: 0.07 deg L, 0.08 deg R
Rear Camber: -1.6 deg L, -1.5 deg R


The car MOSTLY handles really well, surprisingly well and very solid for such a heavy car, but the new stickier tires really have exaggerated that feeling of the rear being disconnected from the front... it feels like there's a big hinge in the middle of the car and it just takes a second for the rear to catch up with what the front is doing. The front turns in like a motha****** though and feels fantastic. I just want the car to feel a bit more connected front to rear.

I haven't done the FRP rear knuckle to toe link bearings which I am guessing makes a good difference here especially with beefier tires and suspension. I was thinking maybe also i made a mistake spec'ing negative toe in the front which makes the front end dive into a turn but the rear is positive which makes it lag behind slightly? I have seen parts like the Steeda IRS Rear Support Braces which im not sure help with this, or if that's more for wheel hop-i dont really launch the car hard so I dont care about wheelhop tbh. I don't want to go nuts with lockouts etc because I still want the car to be decently comfortable eating roadtrip miles and I dont want to hear it from the wifey when we take my car, so really loud solid mounts etc are no good for me.

Thoughts/suggestions? Let me know if I missed something.

If you haven't done so already, I suggest installing a rear subframe alignment and stabilizer kit like the stop-the-hop Ultimate Street or Ultimate Handling sets offered by Steeda. I'm running the street kit and the floaty rear end is now solid.

 

[sms2022]

I have this exact problem and that’s the perfect description, like a hinge. My charger, on 10 year old rubber and weighing 1200lbs more, feels more planted in the corners.

what I’m hearing is steeda brace for sure, white line bushings, and what about the upr billet irs links?

 

[shogun32]

what about the upr billet irs links?

You mean this?
https://www.cjponyparts.com/upr-rear-vertical-link-billet-aluminum-pair-mustang/p/LCA9/

It has value but it's the last item on the Let's fix the rear end, list.

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