car feels very floaty past 70mph after alignment

Kamry

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the car is on rs-r superdowns and 305/30/19s in the rear. attached is my spec sheet and the car feels extremely unstable. the rear end just feels completely disconnected from the car. any advice would be lovely.

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Kamry

Kamry

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Alignment is incorrect
do you have an example spec sheet i should be looking for, for street/backroad driving? iā€™m not very sure what i should be looking for.
 

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Here's my specs OP, although I have similar issues that you have - very floaty and steering wheel vibrations at high speed. Do you also experience any steering wheel vibration at highway speeds and above? That's an annoying issue I'm trying to resolve but so far nothing has worked. Wheel balance is fine according to discount tire and the second BMW shop I took it to to do the alignment, but there's still micro vibrations in the wheel at certain speeds that are super annoying. They are almost like pulsating vibrations - vibrate, stop, vibrate, stop, vibrate, stop.

alignment.jpg
 
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Kamry

Kamry

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Here's my specs OP, although I have similar issues that you have - very floaty and steering wheel vibrations at high speed. Do you also experience any steering wheel vibration at highway speeds and above? That's an annoying issue I'm trying to resolve but so far nothing has worked. Wheel balance is fine according to discount tire and the second BMW shop I took it to to do the alignment, but there's still micro vibrations in the wheel at certain speeds that are super annoying. They are almost like pulsating vibrations - vibrate, stop, vibrate, stop, vibrate, stop.

alignment.jpg
no steering wheel vibrations. tho the car goes slightly to the right when iā€™m not holding the steering wheel
 

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no steering wheel vibrations. tho the car goes slightly to the right when iā€™m not holding the steering wheel
All cars have a tiny bit of steering to the right, especially modern german cars, some say it is for safety some say other things but even my car since new has a had a slight shift to the right after letting go
 

Okvilln

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It is counter-intuitive but toe-in is positive and toe-out is negative so your specs look okay.

A rwd car pushes the front tires. Rolling resistance causes the tires to push back against the suspension. So, rwd vehicles use toe-in settings to offset this movement. More toe-in will reduce oversteer and improve stability at speed. More toe-out will reduce understeer but will reduce stability and make the car feel darty. Excessive toe settings can cause the steering to feel shaky and unstable. It will also cause excessive tire wear.

Here are the OEM specs:

Front-wheel alignment:
Toe-in: Total = 0.27Ā° +/- 0.20Ā°
Camber: -1.75Ā° (+/- 0.50Ā°) with Adaptive variable suspension
Notes: Toe is adjustable. Camber is adjusted by only replacing the steering knuckle.

Rear-wheel alignment:
Toe-in: Total = 0.23Ā° +/- 0.20Ā°
Camber: -2.00Ā° (+/- 0.42Ā°) with Adaptive Variable Suspension
Notes: Toe is adjustable. Camber is adjustable.

Caster: 7.58Ā° (+/- 0.50Ā°)
Steering axis inclination: 17.35Ā°

Looks like your alignment matches factory specs with total toe front and rear at 0.22Ā° and 0.26Ā°, respectively. I also experienced the "floaty" feeling at high speeds until my alignment. My mechanic told me it's due to the adaptive suspension not fully dialled-in with the aftermarket lowering springs plus the moderate toe-in recommendations. My mechanic recommended a more aggressive toe-in for high-speed stability eg. rear toe-in at 0.40Ā° total and going with a proper coilover setup.
 

Okvilln

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no steering wheel vibrations. tho the car goes slightly to the right when iā€™m not holding the steering wheel
If you're in the right lane the vehicle will always drift to the right due to the grade sloping to the right. This is amplified with performance tires.
 
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Kamry

Kamry

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It is counter-intuitive but toe-in is positive and toe-out is negative so your specs look okay.

A rwd car pushes the front tires. Rolling resistance causes the tires to push back against the suspension. So, rwd vehicles use toe-in settings to offset this movement. More toe-in will reduce oversteer and improve stability at speed. More toe-out will reduce understeer but will reduce stability and make the car feel darty. Excessive toe settings can cause the steering to feel shaky and unstable. It will also cause excessive tire wear.

Here are the OEM specs:

Front-wheel alignment:
Toe-in: Total = 0.27Ā° +/- 0.20Ā°
Camber: -1.75Ā° (+/- 0.50Ā°) with Adaptive variable suspension
Notes: Toe is adjustable. Camber is adjusted by only replacing the steering knuckle.

Rear-wheel alignment:
Toe-in: Total = 0.23Ā° +/- 0.20Ā°
Camber: -2.00Ā° (+/- 0.42Ā°) with Adaptive Variable Suspension
Notes: Toe is adjustable. Camber is adjustable.

Caster: 7.58Ā° (+/- 0.50Ā°)
Steering axis inclination: 17.35Ā°

Looks like your alignment matches factory specs with total toe front and rear at 0.22Ā° and 0.26Ā°, respectively. I also experienced the "floaty" feeling at high speeds until my alignment. My mechanic told me it's due to the adaptive suspension not fully dialled-in with the aftermarket lowering springs plus the moderate toe-in recommendations. My mechanic recommended a more aggressive toe-in for high-speed stability eg. rear toe-in at 0.40Ā° total and going with a proper coilover setup.
I appreciate the detailed response, so to alleviate the "floaty" feeling, what did your mechanic dial in the alignment at? is it the .40Ā° rear toe? I'd be very interested in your spec sheet to get my car properly dialed in.

Also, what is your tire setup? anything changed on your suspension also?
 
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Kamry

Kamry

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YOu need to be able to tell the difference between floaty and darty.
Floaty is probably something in the rear. darty is too aggressive/track set up in front.
I'm definitely leaning towards floaty. feels like I make a steering adjustment, front end reacts, then the rear end reacts. once I'm in the turn the car feels stable but coming out of the turn if feels unstable again. this feeling is only at ~60mph and higher.
 

Okvilln

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I appreciate the detailed response, so to alleviate the "floaty" feeling, what did your mechanic dial in the alignment at? is it the .40Ā° rear toe? I'd be very interested in your spec sheet to get my car properly dialed in.

Also, what is your tire setup? anything changed on your suspension also?
Your alignment is set close to factory specs. Keep in mind the specs references total toe-in, not each side. So total toe-in of 0.23 would represent 0.125 each side. If you want more straight line stability add slightly more toe-in on the rears. Ive seen some members with 0.20 toe-in each side.
 

Okvilln

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I'm definitely leaning towards floaty. feels like I make a steering adjustment, front end reacts, then the rear end reacts. once I'm in the turn the car feels stable but coming out of the turn if feels unstable again. this feeling is only at ~60mph and higher.
If you upgraded the rears to 305, did you upgrade the fronts? If not, that may be your clue.
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