S550 mustang floating at high speeds

[jthompson473]

I did the full ford performance track suspension swap and it got rid of all of the problems I had with the stock suspension.

The high speed floating was a BIG concern for me as was the horrible feeling the car had when it broke the rear tires lose, felt like there was no control. Not sure how to describe it but when Id go into a turn it felt like the car turned, then the weight caught up, almost like it was being "pushed" a bit once the weight caught up.

Anyways, the FP track suspension package made the car feel rock solid at high speeds and EXTRMELY more controllable in the corners. When the car does break lose it feels like a good solid slide instead of the madness that happened before. And I cant say enough how planted it feels at high speeds (120+).

Highly recommend the set up though I will say it doesnt lower the car much.

https://www.americanmuscle.com/frpp-assembled-handlingpack-2015gt.html

Thats what I got.

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[NHGTPP1]

Glad to know I’m not insane. lol I may up the wheel width even if that’s not my current issue. I definitely want a correct fit and may wanna go to 305 in the future.
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Glad to know I’m not insane. lol I may up the wheel width even if that’s not my current issue. I definitely want a correct fit and may wanna go to 305 in the future.

Glad to know I’m not insane. lol I may up the wheel width even if that’s not my current issue. I definitely want a correct fit and may wanna go to 305 in the future.

H

Glad to know I’m not insane. lol I may up the wheel width even if that’s not my current issue. I definitely want a correct fit and may wanna go to 305 in the future.

Hello, I've been following this post. I have a 2017 GT Premium, PP1. I bought this used with 9k miles. after about 500 miles, I replaced the rear tires with 305/35R19 on the stock 10" PP1 wheels.
The first time on the highway after the tire change at 70 - 80 the rear end was all over the place. I adjusted tire pressure for maximum contact patch and still had this rear end drift. Recently I bought a new tire / wheel package. The rears are 305/35R19's again but on 11" wheels. My rear end drifting is gone. 70, 80, 90 on sweeping turns, all is good. You may have other issues with your lowering kit, but don't discount the wheel to tire width ratio.

 

[Peter15051]

H


Hello, I've been following this post. I have a 2017 GT Premium, PP1. I bought this used with 9k miles. after about 500 miles, I replaced the rear tires with 305/35R19 on the stock 10" PP1 wheels.
The first time on the highway after the tire change at 70 - 80 the rear end was all over the place. I adjusted tire pressure for maximum contact patch and still had this rear end drift. Recently I bought a new tire / wheel package. The rears are 305/35R19's again but on 11" wheels. My rear end drifting is gone. 70, 80, 90 on sweeping turns, all is good. You may have other issues with your lowering kit, but don't discount the wheel to tire width ratio.

Thank you for bringing this up again. It’s still on my mind as a fix I need to pursue. Car is currently in the shop for a different but minor, unrelated issue. But I’m thinking of ordering 11” wheels for the rear to put on it when I get it back. Currently I’m 295 width so a 10” would probably fix it as well but in the future I want 305 so I’ll probably go 11”. If you don’t mind me asking what wheels you went with specifically so I can look into them—if you’d recommend them that is.

 

[NHGTPP1]

Thank you for bringing this up again. It’s still on my mind as a fix I need to pursue. Car is currently in the shop for a different but minor, unrelated issue. But I’m thinking of ordering 11” wheels for the rear to put on it when I get it back. Currently I’m 295 width so a 10” would probably fix it as well but in the future I want 305 so I’ll probably go 11”. If you don’t mind me asking what wheels you went with specifically so I can look into them—if you’d recommend them that is.

I like these SVE- R350 19x10/11's - Liquid Graphite. 7 spokes allot. The color was much darker than I wanted, But, they are very nice.
https://lmr.com/item/WTK-177913GA/mustang-sve-r350-wheel-tire-kit-graphite-19x10-11-15-17-g2

 

[ShadesOfBloo]

The lower stiffer springs may be mismatched with the stock shocks. If the floating is up and down, replace the shocks with stiffer ones more suited to a lower, stiffer spring.

Both Ford and our sponsors have solutions for this.

CVCashmere

Dang it, I should have thought of that. I'm glad somebody did.

Yes, spring rate and damping rate have to go together and combining stiff springs with stock dampers is a common way for people to mess up their cars' ride and handling.

If I ever changed the springs on my Mustang I was going to get Bilstein B6 dampers.

 

[Peter15051]

Dang it, I should have thought of that. I'm glad somebody did.

Yes, spring rate and damping rate have to go together and combining stiff springs with stock dampers is a common way for people to mess up their cars' ride and handling.

If I ever changed the springs on my Mustang I was going to get Bilstein B6 dampers.

I didn’t know this to be honest. I should’ve just sprung for the coil over handling kit.

 

[ShadesOfBloo]

I didn’t know this to be honest. I should’ve just sprung for the coil over handling kit.

Coilovers are probably overkill, though.

I've seen spring/damper calculations, did some in homework problems, and that's why I was fascinated with coilovers for years. I eventually put coilovers on one of my cars. My experience with that car's ride is why I won't buy coilovers for a street car again. Matching springs and dampers won't make up for replacing your rubber strut mounts with metal "pillow ball mounts".

A Mustang GT has struts and shocks that are soft even for stock springs. I've read elsewhere on this forum that lowering springs are basically guaranteed to suck if you leave stock dampers on the car. A LOT of aftermarket dampers are made to go with lowering springs.

Hence, my suggestion for Bilstein B6. They're generally made to go with Eibach springs which, for the Mustang, are stiffer than my stock GT-PP springs and probably as stiff as your Ford springs.
They've been combined with lots of different springs, and made the owners happy.
(Heck, I'd probably put them on my Mustang even if I don't change the springs.)

Some others, including the ones from Ford Performance, also look like valid choices.

 

[CrazyHippie]

ford puts 275's on everything from 9.5 to 10.5 because they work well on that size rim.
I want to run 275/40/19's all the way around when i get some square setup wheels.

your issue, though, is one of 2 things: bad alignment or broken parts.

imo a good set of springs and struts is what you need with all that power, though.

one thing that really helped with stability was the toe l ink bushings from ford performance.

if it was a bad hub you'd likely hear an awful roaring sound from that side that increases with speed (and it would eventually weld itself together internally).

I'm currently waiting on a square set of 19x9.5 / 275×35. Any idea of pros and cons of 40 vs 35 sidewall?

 

[Johnny Rockit]

I haven't been over 130mph and so far feels like it us on rails. Super tight. Just 4k miles on the clock.

 

[Oakley]

I'm currently waiting on a square set of 19x9.5 / 275×35. Any idea of pros and cons of 40 vs 35 sidewall?

i like 40 sidewall for better ride quality. 35's leave too much gap and lower the car a quarter inch.
anything i can do to avoid lowering the car more than i have to and jacking with ride quality will be on the table.

 

[CrazyHippie]

i like 40 sidewall for better ride quality. 35's leave too much gap and lower the car a quarter inch.
anything i can do to avoid lowering the car more than i have to and jacking with ride quality will be on the table.

I think that my preferences are aligned with yours. I don't mind lowering the car a quarter inch, but the increased gap and firmer ride will probably push me towards either a 275/40 or a 285/40 when I need a new set of tires. The stock gap is already fairly substantial. Thanks for the advice!

 

[Garfy]

Side to side like a fish tail. Only about 80mph it starts. By 100 it’s scary

You must have some serious problems at only 80 mph. I have a mere base GT and just returned from a road trip to NV and on the way back I had exceeded 105 mph a few times when passing vehicles on a 2-lane highway. Never had any issues or "floating" feeling at all; car was firmly planted and very stable (I clearly could do 120 or more easily but didn't know the area or where the troopers might be hiding).

 

[Peter15051]

You must have some serious problems at only 80 mph. I have a mere base GT and just returned from a road trip to NV and on the way back I had exceeded 105 mph a few times when passing vehicles on a 2-lane highway. Never had any issues or "floating" feeling at all; car was firmly planted and very stable (I clearly could do 120 or more easily but didn't know the area or where the troopers might be hiding).

I’m of the same mindset. If my wife’s Subaru is more stable than my mustang at that speed there’s an issue.

 

[Tadas]

I’m of the same mindset. If my wife’s Subaru is more stable than my mustang at that speed there’s an issue.

Did you find a problem?

 

[shogun32]

If you have any driver aids like lane keeping on, turn it off. It's the new hot mod for the m7g guys who wete stupid enough to think tech (Ford tech no less) is always a plus.

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