ChrisUlrich

At the track, at above i'd say 125mph, the steering wheel begins to pull left and right. At 150mph it's damn near a death sentence to go any faster.

I had the car aligned, and it went away. But a few days later, it came back! Brought it back to be aligned again, but haven't gotten the chance to test it out. But the dude who worked on the car said that there wasn't anything to fix on the alignment.

Just wondering if anyone has any idea what it might be.

icntdrv55

Is your F:R tire stagger stock or within a few % of stock? Possibility that you're experiencing Active Handling intervention with the front brakes? That's assuming there isn't a hidden mechanical problem...

ChrisUlrich

The front brakes do vibrate when I apply them at those speeds.

What could do that be? The tires are nothing special. Michelin Super Sports on an 18" rim.

jaredtxrx

What kind of C6 do you have?
Any exterior modifications?
Any suspension modifications?
What size front AND rear tires do you have?

icntdrv55

Pulsing or intermittent grabbing of the brakes--F or R--would indicate either warped rotor(s) or a rough/corroded/rusty/burnished spot, possibly from overheating. As for stagger that I mentioned, are you running the stock rim and tire sizes both F&R? If you aren't running stock sizes, you need to recalculate your F:R tire diameter ratio to ensure you stay within the factory specs. As I recall, the standard ratio on a late-model GS is about 1.046. As a guess, I'd say staying within 2-3% of that would be advisable.

ChrisUlrich

255/40/18
295/35/19

jaredtxrx

What kind of C6 do you have? (I'm not guessing a narrow body based on tires)
Any exterior modifications?
Any suspension modifications?

Any brake modifications?

ChrisUlrich

No exterior modifications
Z06/GS front brake upgrade
Z51 shocks
Eibach Sway Bars

I had 305/35/19 NT05R's put on yesterday.

Had the 255/40/18 MSS rebalanced as well.

Should the car be aligned after swapping rears and rebalancing fronts?

I didn't get a chance to test it out yet. The front tires were out of balance (although not terrible). We will see what happens with that.

thank you in advance for whatever advice you can give!

jaredtxrx

My guess is that if you aren't experiencing any issues until 125+mph it is aerodynamics related. C6's tend to raise the front when getting up over 120mph and can get floaty. This will make anything that normally wouldn't be felt start to be felt very quickly.

I would go back through the sway bars and make sure everything is buttoned down well. But my guess is that you would head some kind of knocking or clicking if you had some loose bolts.

Have you noticed any extra brake dust on a particular wheel at all? It could be you have a caliper that is a little hung up but isn't noticeable until your front end is lightened up by your speed. Of course it could be the unbalanced wheels causing the issue at speed as well or the alignment. I could be just about anything at this point and I'm not being very much help, lol.

The only other thing I can think of is trying someone else on the alignment if things still aren't feeling sorted out.

ChrisUlrich

replaced the rears with the NT05R's and had the fronts rebalanced. That did the trick.