3.3TT Car feels 'floaty' at high speeds

[Jimmer]

This might not be your solution, but what setting is your lane keep assist? I will say that I had a lot of the same feelings about my car within the first week. Even wondering about alignment despite the car driving straight. After deactivating Lane keep assist one rainy night, the entire attitude of the car seemed to change. Just an idea. I won’t go back to using the active lane keep assist, it really gave me a “floaty” and somewhat disconnected feeling from my car and the road.

I know I wont put it back in till I have a long drive. I mean I like the feature, but not for daily driving with tons of traffic.

 

[brancky3]

This might not be your solution, but what setting is your lane keep assist? I will say that I had a lot of the same feelings about my car within the first week. Even wondering about alignment despite the car driving straight. After deactivating Lane keep assist one rainy night, the entire attitude of the car seemed to change. Just an idea. I won’t go back to using the active lane keep assist, it really gave me a “floaty” and somewhat disconnected feeling from my car and the road.

It's off. Absolutely terrible on my drive as I'm always on back roads which are narrower than highways so it just keeps beeping and corrects me all the time lol

 

[only1harry]

This might not be your solution, but what setting is your lane keep assist? I will say that I had a lot of the same feelings about my car within the first week. Even wondering about alignment despite the car driving straight. After deactivating Lane keep assist one rainy night, the entire attitude of the car seemed to change. Just an idea. I won’t go back to using the active lane keep assist, it really gave me a “floaty” and somewhat disconnected feeling from my car and the road.

That might be it! I hope it's the solution for the OP and for everyone else that feels the same about the car's ride at hwy speeds.

BTW, the sticker on the door of the 2019 GT AWD I test drove yesterday said: 36 psi front, 39 rear. It had the 18" wheels with the same tire size all around. It sounds like the 2018's might have different recommended pressures.

 

[MerlintheMad]

That might be it! I hope it's the solution for the OP and for everyone else that feels the same about the car's ride at hwy speeds.

BTW, the sticker on the door of the 2019 GT AWD I test drove yesterday said: 36 psi front, 39 rear. It had the 18" wheels with the same tire size all around. It sounds like the 2018's might have different recommended pressures.

No. They are the same. The staggered psi is 38/36 front/rear. Squared is opposite, lower in front, higher psi in the rear. Don't know why.

 

[RVance]

I have the GT2 AWD. I've taken two round trips from Crescent City, CA to Oceanside, CA via Grants Pass, OR/I-5. Hit 120 in short bursts several times between Ashland, OR and Redding, CA for passing "emergencies." Always feel planted and solid, especially when I nail the Brembos to take me back to impulse drive.

 

[only1harry]

No. They are the same. The staggered psi is 38/36 front/rear. Squared is opposite, lower in front, higher psi in the rear. Don't know why.

Wow, it's the opposite with my 335i with staggered setup - 35F/39R. M3/M4 is the same way. Probably because the rear tires are lower profile than the front. I have 245-40's in the front and 255-35's in the rear. Does the Stinger's staggered setup not have lower profile in the rear? That might explain it, but it's pretty unusual to see a higher pressure in the front with staggered.

 

[MerlintheMad]

Wow, it's the opposite with my 335i with staggered setup - 35F/39R. M3/M4 is the same way. Probably because the rear tires are lower profile than the front. I have 245-40's in the front and 255-35's in the rear. Does the Stinger's staggered setup not have lower profile in the rear? That might explain it, but it's pretty unusual to see a higher pressure in the front with staggered.

The staggered 19" GT rims have an 8" wide tread in front, and 8.5" in the rear. The tire sizes are: 225/40 and 255/35 respectively.

 

[Dochidalgo]

No. They are the same. The staggered psi is 38/36 front/rear. Squared is opposite, lower in front, higher psi in the rear. Don't know why.

About the reasons why the psi is higher in the front than the rear, in a RWD car, are the engine and all the accessories weigh more than the rear, so the tire needs more air pressure to support that weight. The rear tires are the traction who needs more tire contact area (tread) with the ground, less air pressure lets the tread and the shoulder contact completely to the ground.....Not sure if i make this clear.

 

[RVance]

About the reasons why the psi is higher in the front than the rear, in a RWD car, are the engine and all the accessories weigh more than the rear, so the tire needs more air pressure to support that weight. The rear tires are the traction who needs more tire contact area (tread) with the ground, less air pressure lets the tread and the shoulder contact completely to the ground.....Not sure if i make this clear.

I have read different explanations for inflation pressures: that the tire's inflation is determined by several factors for optimal traction, rolling resistance, heat tolerance, load rating, etc. But lower pressures don't necessarily translate to more contact area and a "softer' inflation doesn't mean you will get better traction with a lighter weight load or in slippery conditions, either. Lower pressures can actually cup the contact patch and burden the edges, while offering less traction and contact. Optimal inflation will open the tread to its most effective formation and broaden the contact patch. I'm guessing that recommended pressures may not necessarily relate to the added weight of the front end, but I could be wrong. My Mustang is heavier by far in the front end, but all tires get the same air pressure. My Stinger AWD is heavier in front than a RWD, but the same inflation is recommended for both models. Or, I could be full of shit and your explanation could be right.

Additionally- I've read the air in the tire doesn't "support" the weight. Oddly, the tire hangs on the rim and it's the sidewall that carries the weight. Inflation only expands the tire to its proper dimensions to facilitate this function.

 

[only1harry]

I have read different explanations for inflation pressures: that the tire's inflation is determined by several factors for optimal traction, rolling resistance, heat tolerance, load rating, etc. But lower pressures don't necessarily translate to more contact area and a "softer' inflation doesn't mean you will get better traction with a lighter weight load or in slippery conditions, either. Lower pressures can actually cup the contact patch and burden the edges, while offering less traction and contact. Optimal inflation will open the tread to its most effective formation and broaden the contact patch. I'm guessing that recommended pressures may not necessarily relate to the added weight of the front end, but I could be wrong. My Mustang is heavier by far in the front end, but all tires get the same air pressure. My Stinger AWD is heavier in front than a RWD, but the same inflation is recommended for both models. Or, I could be full of shit and your explanation could be right.

Additionally- I've read the air in the tire doesn't "support" the weight. Oddly, the tire hangs on the rim and it's the sidewall that carries the weight. Inflation only expands the tire to its proper dimensions to facilitate this function.

You are correct on most points. Lower pressures in the rear are not just because the rear is "lighter", and lower pressure does not equate to optimal traction or contact patch. The right pressure or the one recommended by the manufacturer is the one that provides optimal handling without increasing tire wear, without rolling over the sidewalls under "normal" driving, and what gives you the best gas mileage at the same time among other things. Tire pressure also depends on the size, weight and characteristics of the tire, the car's suspension behavior and geometry (this is a big one), weight at the car's corners, and other factors such as manufacturers look to provide the best ride comfort. It's a lot of things to consider and balance when coming up with the right tire pressures.

My 335i has the same exact staggered setup with 225-40 up front and 255-35 in the rear and the recommended pressures by BMW is 35F/39R. The opposite of the Stinger RWD. Also like you said the AWD Stingers get higher pressure in the rear, at least on the 2019 GT AWD I test drove with the door sticker stating 36F/39R, when we no they are heavier in the front. So that tells us that depending on how the car is set up (GT does not have the adaptive suspension for ex.) plays a big role on how the tires should be inflated. It really is highly dependent on things like suspension geometry (including spring rates, shock valving, sway bars, etc.) how the power is distributed to the wheels, and some of it is weight, and also the amount of down forces during cornering, etc., but it's not "weight" alone. The majority of the cars are heavier in the front but recommended pressures by the manufacturer are the same all around. Also on some cars such as BMW, run-flat tires are used as an integral part of the suspension to compensate for a soft suspension, because RF tires are harder than regular tires with much stiffer side walls. So those cars can have recommended pressures that don't make sense or are out of the norm, or not what we are used to seeing.

Also when you upgrade the Stinger's sway bars, or you install Eibach springs, you can forget about those tire pressure numbers behind the door. They are no longer valid or optimal for your Stinger after you have modified the suspension.

 

[Luc]

Also when you upgrade the Stinger's sway bars, or you install Eibach springs, you can forget about those tire pressure numbers behind the door. They are no longer valid or optimal for your Stinger after you have modified the suspension.

That makes sense, I don't know why it didn't occur to me earlier! How would one know the correct new tyre pressure numbers after any kind of mod? Is there a formula or something? I'm sure we would all want to drive with the correct specs to avoid any issues no matter how small

 

[Goodmang37]

I have had my GT at 100+ MPH on many occasions on the interstate with no floating whatsoever.......but the AMG Mercedes I traded in did have a tendency to feel like floating at these speeds.

 

[MerlintheMad]

Also like you said the AWD Stingers get higher pressure in the rear, at least on the 2019 GT AWD I test drove with the door sticker stating 36F/39R

Backwards. The RWD has higher psi in the rear; the AWD has higher psi in the front. If Kia changed the GT2 MY19 to be 36F/39R that is a revelation to me. Why would they do that?

 

[nhcowboy28]

Backwards. The RWD has higher psi in the rear; the AWD has higher psi in the front. If Kia changed the GT2 MY19 to be 36F/39R that is a revelation to me. Why would they do that?

Right out of the 2018 AWD manual

18” all seasons
36 psi F, 39 psi R

19” staggered Summer tires
38 psi F. 36 psi R (AWD)
36 psi F, 36 psi R (RWD)

 

[Waynerm002]

Merlin, you gotta look stuff up some times. As you know not everyone always post correct information.

 

[only1harry]

Right out of the 2018 AWD manual

18” all seasons
36 psi F, 39 psi R

19” staggered Summer tires
38 psi F. 36 psi R (AWD)
36 psi F, 36 psi R (RWD)

Thank you. I don't know how many times I wrote AWD and 18" And I can confirm - I read the sticker behind the door 2 days ago on a 2019 GT AWD with 18" - 36 front, 39 rear!!

 

[MerlintheMad]

Right out of the 2018 AWD manual

18” all seasons
36 psi F, 39 psi R

19” staggered Summer tires
38 psi F. 36 psi R (AWD)
36 psi F, 36 psi R (RWD)

Welp, all I can say is "I'll be swizzled" (and more careful, but not perfect ). I thought we were talking about 19" staggered rims. And I read on here that the RWD 19s have higher psi in the rear; so I didn't check the manual. I will correct my memory with this authoritative info. Thanks.

Thank you. I don't know how many times I wrote AWD and 18" And I can confirm - I read the sticker behind the door 2 days ago on a 2019 GT AWD with 18" - 36 front, 39 rear!!

Somehow I missed 18" AWD. My AWD is 19". (read for comprehension, Dougie )

 

[only1harry]

No worries Merlin. I am new here but from what I can see you contribute a lot, so thank you. I try to help when I can, and put my almost 20 year experience auto-xing, road racing, and trying different suspension setup's to good use.

Now I wonder if Koni or Bilstein are coming out with adjustable shocks for the Stinger any time soon Something that will match progressive Eibach springs better or even non-progressive ones for some track use (dare I say).

Harry