S550 mustang floating at high speeds

[Brisvegas]

Being FI you should have really stiffened up the back end with IRS kit and stop the hop , but it really does sound like alignment . Toeing out on the rear be my best guess , makes it a bit darty . Would be looking to stiffen up rear end regardless .

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[CVCashmere]

Peter

I went with a used, complete set of Ford PP1 springs, shocks, sway bars, vertical and horizontal links.

However, before spending money, check out the advice from LowPSI, KingKona, etc. They have identified several factors that must be checked first.

CVCashmere

 

[baevid]

I would definitely check your alignment specs. There should not be any stability issues at freeway or slightly excessive freeway speeds.... unless you're flooring it for no reason in inclement weather . And yes recheck your suspension install and wheel bearings for issues.

I've done Texas Mile events with 305/35R18 rear tires with no issues in the 180-210mph range.

 

[speedfrk]

Did the car do this when stock and new? Having a lot of experience racing superbikes, I'd suggest doing the obvious- check the alignment at another shop than the one that did it originally. Then go back to stock and change one thing at a time. Put the stock wheels and tires back on for a test and then you have another data point. When you change a bunch of stuff all at once, you'll chase your tail forever.

 

[Peter15051]

Peter

I went with a used, complete set of Ford PP1 springs, shocks, sway bars, vertical and horizontal links.

However, before spending money, check out the advice from LowPSI, KingKona, etc. They have identified several factors that must be checked first.

CVCashmere

Yep, I’m literally taking note to ask them about when the shop calls. One other thing of particular interest someone said is my tires may be too wide for my rims in the rear. I remember actually telling the guy at discount tire that I was pretty sure we needed to go down to 275 with a 9.5” wheel or 285 max. But he insisted his system said 295 would work. I go the tires a few days after I bought the car so for all I know it could be a contributing factor. I’ve never had incorrect width so I’m not sure what the results would be. However I’m not opposed to putting 10.5” wide on the rear to accommodate the rubber better.

 

[Oakley]

Yep, I’m literally taking note to ask them about when the shop calls. One other thing of particular interest someone said is my tires may be too wide for my rims in the rear. I remember actually telling the guy at discount tire that I was pretty sure we needed to go down to 275 with a 9.5” wheel or 285 max. But he insisted his system said 295 would work. I go the tires a few days after I bought the car so for all I know it could be a contributing factor. I’ve never had incorrect width so I’m not sure what the results would be. However I’m not opposed to putting 10.5” wide on the rear to accommodate the rubber better.

you were right and he is wrong. don't care what the computer says.

 

[Peter15051]

you were right and he is wrong. don't care what the computer says.

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.

 

[bnightstar]

I just spoke to the accessory guy at the dealer. He said he will do some research but he suggested starting with track pack away bars.

check your wheel hubs mostly rear left one. Usually side to side float is a sign of a wheel hub going bad.

 

[Oakley]

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).

 

[JetGray_Mach1]

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.

Yeah man those guys are morons. They pissed me off when they mounted my tires incorrectly with my staggered setup. They put 315s(on the narrower rims!) on the front and 305(wider rims) in the back

 

[Bluemustang]

Hey guys, I know it is very common for mustangs to have a floating feeling or feel like a slow side to side motion at high speeds—what I want to know is from those who have eliminated this issue, what did you do? I’m on ford lowering springs 1” drop all around, otherwise suspension is stock. I have aftermarket wheels and tires. Michelin pilot sport 4s 255 up front and 295 in the rear. Wheels are 19x8.5 front and 19x9.5 in the rear drag dr 37.
I’ve seen some guys claim tightening a single bolt fixed this, may be true but seems very simplistic. I’m thinking to do a coil over kit for a fix. Your thoughts and experience.

Which 295s? If it's 295/35R19, they're too wide. If it's 295/30R19, they're definitely too wide for that wheel width and you have to change them. That could be your problem right there.

Tires
Alignment
Check bushings clocked properly
Wheel bearings

Don't go throwing more money at it to fix and obvious issue a stock, functioning car wouldn't have.

 

[Bluemustang]

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.

Not all tire specs are the same. 295/30R19 and 295/35R19 are radically different in MPS4S.

 

[KingKona]

Yep, I’m literally taking note to ask them about when the shop calls.

Ask who? About what?

I think you need to settle on one thing;

Shops don't know shit about modifying cars, or S550s in specific. They can align the car to factory specs, put on new tires, do basic maintenance and repairs, but they don't know a damn thing about modifying.

You've mentioned a few times about asking your "shop" about this and that.

Stop it.

It's your job to tell them what you want done. They don't know their asses from a hole in the ground.

Lastly; what PSI are you running your tires at?

 

[MAGS1]

Not all tire specs are the same. 295/30R19 and 295/35R19 are radically different in MPS4S.

This is correct.

OP, check out Tire Rack’s site. They list all the specs including recommended wheel width range for each tire size. They will also give a measured rim width, this is the optimal size wheel for that tire size. 295 is too large for a 9.5” wheel, it’s a better fit on a 10.5” wide wheel

 

[Bluemustang]

This is correct.

OP, check out Tire Rack’s site. They list all the specs including recommended wheel width range for each tire size. They will also give a measured rim width, this is the optimal size wheel for that tire size. 295 is too large for a 9.5” wheel, it’s a better fit on a 10.5” wide wheel

Yes I agree. Also I prefer to use Tire Rack's Tread Width also to fit tires for best handling. The 295/35R19 has a tread width of 9.8" which is too wide. For 295/30R19 they show a tread width of 11". I would use that tire for an 11" wheel. For a 9.5" wheel I'd look for tread width between 9-9.5". He can use all of the tires contact patch and even a tiny bit of stretch can be a good thing for a better breakaway characteristics.

What he doesn't want is a tire fitting too loose. It can cause tread squirm which will make handling unpredictable. If it's much too wide it can compromise the sidewall because it's not properly support by the wheel width.

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