2019 STI - New wheels/tires, now it's darty/wobbly under acceleration

[DJBunyan]

Hey guys,

Like the title says, I (and by "i" I mean costco lol) just put my winter setup on my '19 STI today and now the car seems to be "wobbly" or unstable under acceleration.

If I had to pick a side it was pulling to, I'd say right, because the one time I actually let my hands off the wheel and hit the gas, it pulled right. but it's not a clear cut "pulling to one side" issue overall, It's just more that under hard acceleration, the front end now seems to almost "float" a little bit and get a little wobbly and I need to keep a firm grip on the wheel and keep adjusting. This is my first performance car btw so my lack of other experience may be making explaining this extra difficult. Hopefully everything I'm saying is making sense.

The car felt rock solid under acceleration in its stock form. This is a new issue that was apparent immediately after I put the new tires and wheels on today.


Car in its current state seems rock solid on the hwy, not really getting any bad vibrations or anything like that


Wheels: 18x8.5 +44 Rota Titan

Tires: Blizzak WS90 245/40r18



Any ideas guys? I tend to be on the anxious side so I'm really hoping I'm just overthinking things. However, I noticed it immediately as I pulled out of the shop and have since done about 50 miles of test driving tonight and I really don't think I'm just being paranoid. It's minor overall but definitely drives different than it did this morning.

Bad Alignment?

Just a different feeling with the winter tires that are softer and have a taller sidewall?

the wheels that are an inch smaller and nearly 10lbs each lighter than the stocks making things feel less stable?

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[fullah]

Having put snow tires on my car as well I think this is just from then being too soft and mushy. We haven't seen snow in my area yet so the roads are still dry. This will cause the tires to feel like they're pushing and pulling side to side since the roads have a lot of friction on the tires. This gets worse when the temperatures are in the 50s like it is where I am at. I upped my tire pressure to 35 psi front and 34 psi rear as the factory psi specs on your door are rated for 60 degree ambient temperatures. The owners manual says to increase pressure as the temps go down. I think it's section 11-30. The general rule of thumb is 1 psi higher for every 10 degrees below 60 degrees ambient temp. The increases pressure helped me with the floaty feeling.

For what it's worth I'm using 225/55/17 instead of 245/40/18 so definitely have a taller side wall than stock. I went with a more narrow tire because it was not only cheaper but narrow tires help cut thru the snow easier.

[ronemus]

There may be a piece of crud captured between the mounting faces of a wheel and hub, which would create a wobble - the mechanic SHOULD clean those surfaces, but the crush of peak season and a high-volume/low-cost operation may have resulted in some cut corners.

[speedyHAM]

Originally Posted by ronemus

There may be a piece of crud captured between the mounting faces of a wheel and hub, which would create a wobble - the mechanic SHOULD clean those surfaces, but the crush of peak season and a high-volume/low-cost operation may have resulted in some cut corners.

This is spot on. First thing would be to remove the wheels, clean the surfaces and remount the wheels. If there is still a problem then I would get the alignment checked.

[Norm Peterson]

Originally Posted by DJBunyan

Hey guys,

Like the title says, I (and by "i" I mean costco lol) just put my winter setup on my '19 STI today and now the car seems to be "wobbly" or unstable under acceleration.

Wheels: 18x8.5 +44 Rota Titan

Tires: Blizzak WS90 245/40r18

New tires still have some mold release agent on the treads. It takes some driving to scrub it off.

Winter tires have smaller tread blocks than summer tires (making them more flexible) and the tire carcasses probably aren't as stiff either since they don't need to be for the slower speeds you're at under snowy and other winter conditions. This flexibility typically makes them feel a little less "stuck down" compared to your summer tires. Especially on dry pavement.

They should improve somewhat after driving on them for a while, but it's a good idea to avoid beating up on them with hard acceleration or hard cornering and avoid hard braking as much as possible for the first few hundred miles.


Norm

[Lee-online]

I purchased a set of Prodrive wheels and had a set of Pilot Sport A/S 3+ tires mounted. One of the best rated UHP all seasons and yet they really changed the handling. Soft turn in, mushy ride and drifts wide on exit. When pushed, I can hear and feel the tires gripping but it is a completely different feeling from the stock tire. I have gained confidence in the tires over the last 2 weeks.

The tires are now 18" so more flex in the sidewall, more tread blocks and a softer compound. I knew the handling would change and its the reason i didn't get a snow tire.

Did the new wheels require a hubcentric ring?

[Patrick Olsen]

Originally Posted by DJBunyan

Tires: Blizzak WS90 245/40r18

Just a different feeling with the winter tires that are softer and have a taller sidewall?

Have you ever had dedicated winter tires like this on another car? IMO what you're feeling is simply the difference between the performance-oriented stock summer tires and the squishy, full tread depth ice & snow tires that you have on the car now. It's a very noticeable difference, and can be a bit disconcerting the first time you feel it.

I suppose it can't hurt to take the wheels off and ensure the mounting surfaces of the rotors were properly cleaned, but I'd be willing to bet you won't find anything wrong there.

Where are you located? Depending on where you are and what type of winter driving conditions you expect, it may be that a performance winter tire would've been a better fit. They're still squishier than a summer tire, but the difference isn't nearly as great as it is with the studless ice & snow tires you've got now.