car feels very floaty past 70mph after alignment

[AustinGRSupra]

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.

Yep. I’ve got mine at .2 each side for total toe in rear of .40.
I also have 0 toe in front.
No floaty feeling here.

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[Kamry]

If you upgraded the rears to 305, did you upgrade the fronts? If not, that may be your clue.

I upgraded to 275/35/19 in the fronts but they were rubbing with my current wheel setup so i had to go back to 255/35/19

 

[Kamry]

Yep. I’ve got mine at .2 each side for total toe in rear of .40.
I also have 0 toe in front.
No floaty feeling here.

are you on stock springs? also what's your rear camber?

 

[AustinGRSupra]

are you on stock springs? also what's your rear camber?

Stock suspension. Rear camber is -1.8.

 

[Msoupe]

@Kamry
Your thread title says the car felt floaty after alignment. Does that mean it didn't feel that way before? Technically, your before measurements indicates your left rear was toe out, which would have made the car more unstable before the alignment. I think for safe stability with high power rear wheel drive cars, your total toe should be closer to 0.40°. Also, make sure your not riding on the bumpstops in the rear. Most drop springs will get the rear shock riding pretty deep into the bumpstops, so If RSR springs do not provide shorter rear bumpstops than I'd check your shock travel.

In general, the Supra inherently has a flaw of delayed rear response. That feeling of front responds and the rear responds a second later. This could be tire squirm, rubber bushing deflection in control arms, etc. Maybe someone who has replaced all of their rear control arms with heims and upgraded stiffer side-wall tires can chime in on their impressions.

 

[focusmade]

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.

Did you figure out the vibration issue? Mine recently started doing this too.

 

[gdi2290]

whats your rim width front/rear? do you have spacers?

pulling to the right is the caster problem

 

[94boosted]

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

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

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

Looks like your alignment matches factory specs with total toe front and rear at 0.22° and 0.26°, 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 0.40° total and going with a proper coilover setup.

Any chance anyone has the part number for the steering knuckles, the camber correction ones?

 

[razorlab]

Any chance anyone has the part number for the steering knuckles, the camber correction ones?

 

[94boosted]

Thanks a bunch razorlab, and to be sure before I drop a stupid sum of money on these, for more negative front camber I'd obviously want the -30 knuckles? 43211-WAA02 & 43212-WAA02?

 

[razorlab]

Thanks a bunch razorlab, and to be sure before I drop a stupid sum of money on these, for more negative front camber I'd obviously want the -30 knuckles? 43211-WAA02 & 43212-WAA02?

I would assume so but I don't have hands on experience with these yet.

FYI, here are the BMW part #'s for the Z4:

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