Car swaying side to side at high speeds

[Bluemustang]

Not sure if this is causing the problem but geometry is definitely altered with that drop.

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[Bluemustang]

90-100mph! You bad boy! But seriously, when you substantially change one part of the suspension you end up changing it all unless you just lowered it for looks. Found out about that over 3 decades ago and don’t intend to repeat the experience.

Bingo. I discovered this the hard way as well. This car was my first to modify the suspension.

There's many things that lowering spring manufacturers don't tell you in the product description - all of the potential negative effects. Depending on the springs - if no other changes are made you could end up making it a worse handling car instead of better. But they don't tell you that because they're trying to sell you and a lot people just do it for looks anyways.

The suspension is a system. Most times one change necessitates other changes unless it is thought out very carefully.

 

[NightmareMoon]

If you didn't get an alignment after lowering, definitely do that immediately. Your rear toe could be dangerously off and causing issues like this. If the toe is wonky, there is no other fix except to fix the alignment.

Wheel hubs issues are most easily checked by jacking up that corner of the car, and then gripping the wheel from opposite sides (top/botton, left/right) and trying really hard to wobble it with as much leverage as you can manage. If there is any play in the wheel, then the hub is toast. Handling gets really squirrely if the hubs have any play in them. Very dangerous to drive hard on a wheel hub thats going out. If i a hub is starting to go, you might hear a 'ping' on accel or decel with the windows down. If you let it go for a while, the hub may start making a constant noise.

With a correct alignment (0.2 to 0.3 degrees total toe in), its quite normal for mostly-stock suspension S550s to slowly wiggle their butts when you've got tire spin (at any and all speeds). Are you getting wheel spin at the high speeds mentioned?

If you're hooked up and not spinning wheels, it should track straight unless there is a hub or alignment problem. Most tires won't grip at low speeds so most cars will do this with wheelspin in 1st or 2nd. If you've got wheelspin at 90 mph with stock power, your chosen tire is not so great. If the alignment and hubs are good, and you're getting undesirable but normal side to side wiggle due to wheelspin, then you can address it with certain upgrades to the rear suspension cradle and suspension bushings to remove play in the stock rubber components, and/or get tires that hook up.

I can't speak for running stock shocks with your specific springs and tires, but this isn't the first report of a car doing this at high speeds with Nittos. I'd definitely have the car aligned and check the wheel hubs for play first, and then if you don't find any issues with those two likely suspects, then we can proceed to suspension upgrades or some undesirable interaction between your springs, shocks, and Nitto tires.

 

[BrettT]

Just regular nitto street tires, tire pressure was like 35 psi.

What was the air temperature at the time? Was that the actual tire pressure at the time?

 

[rayban1]

I had the sportlines, never installed and went with BMR 089/082 springs because of this review,
Glad I did very happy with the BMR set up on my car........

 

[MSMStannyl]

Has anyone else experienced this? The other day I was on the highway and i decided to do a hard pull. I noticed that the rear end of the car started to feel like it was moving side to side...almost like it was floating. I think it only does it when it's over 90mph/100mph. I drive around 80mph most of the time without any problem. The car is lowered on springs. Stock 19inch performance package wheels. Tires are pretty much brand new. Wheels were balanced and aligned after being lowered.

2015 GT PP

Some good suggestions here for things to check but I noticed that you said your tires were pretty much brand new. New tires will be very slippery for a few hundred miles as the oils burn off. I remember after getting my new tires I thought the same thing. My car felt extremely unstable for a while until the oil burned off. Then everything was fine. That's probably your issue right there. That said, def get an alignment if you changed out the springs.

 

[NoVaGT]

I'll still go with a lowered car on the OEM struts and shocks. That's a bad combo, as the OEM struts and shocks are know to be an issue with lowering springs.

Check out some Steeda shocks & struts, plus the other IRS stuff they offer. A really complete suspension set-up really changes the car.

 

[phillybob232]

I've been on lowering springs w/ stock shocks and struts for a bit over a year now. Really like the look, and I like the reduced body roll and nose dive under braking. However, I've gotten fed up with the ride quality and stability.

I snagged a set of the Ford Performance track shocks and struts and will be installing soon, once the weather is nice enough to bother

 

[Bluemustang]

I've been on lowering springs w/ stock shocks and struts for a bit over a year now. Really like the look, and I like the reduced body roll and nose dive under braking. However, I've gotten fed up with the ride quality and stability.

I snagged a set of the Ford Performance track shocks and struts and will be installing soon, once the weather is nice enough to bother

You won't regret that. I wanna hear how it feels when it's done.

 

[Hack]

When you had the rear suspension apart, did you replace the nuts that retain the driveaxles to the rear hubs? If you don't use new nuts they will back out and you will have symptoms like you are describing.

 

[Bondo2011]

My GT is lowered (got it that way) with CJ Pony Parts springs. Mine swayed a lot when I got on mine, I went and got an alignment and my rear wheels were whacked! Got it aligned and it fixed my issue!

 

[5ABI VT]

side to side or self rear -steering feel is in my experience the toe. Were the toe arms loosened or undone when installing the rear springs?

 

[Roadway 5.0]

Have your alignment checked. As the previous two posts have mentioned, your toe is likely off. FYI, I intentionally add more toe-in to the front of my car (.10 each) for the high speed driving in my area. Rears are at the Ford recommended .12 each. Holds steady and tracks straight all the way to 150mph.

 

[TYGT350]

Funny I found this thread. I was just recently experiencing this issue. I just always assumed it had to do with the road surface with a staggered setup (tram lining). I'm lowered on Eibach Pro-Kits (1.1" front 1.0" rear) stock PP shocks/struts. 20" wheels 275 up front 315 in the back. 30psi rear tires. Same thing happens to me when I do pulls at the high rpm it begins to sway/wobble. Speed doesn't seem to be the sole factor though. Because the higher in the rpm range I go it gets worse, for example do a pull in 3rd all is fine but as I get into the upper rpm range it starts to sway/wobble, do a "long" shift and the swaying goes away, go into 4th continue pulling doesn't sway initially then again as I get in the upper rpm starts to sway/wobble again. I doubt i'm spinning my tires at these speeds with my power level and my tires. Car has 15K miles probably about 10k with the springs on


Figured when I eventually get a square setup maybe it would remedy the issue but it sounds like a plethora of possible problems. For one I guess I need a new set of shocks/struts, second another alignment?

 

[CEHollier]

Did you reindex (clock) the bushings after lowering the car? They are set to a higher ride and tightened for that height. Lowering the car with that factory ride height they are now in a bind. Other members who did not reindex the bushings after lowering their car report what you did.
This link is long but full of a lot of good information.
https://www.mustang6g.com/forums/th...-lowering-your-s550.44129/page-8#post-2282569

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