After 4-wheel alignment, handling is very twitchy.

[Retroman1969]

I've been meaning to post this question, but keep forgetting until now.
A few weeks ago I put on new rear tires and had a 4 wheel alignment done along with having much of the negative camber taken out of the rears for a more neutral tire-saving setting.
Ever since, the handling of the car has gone from smooth and linear to twitchy and unstable.
It's hard to describe, but when steering into curves or making quick maneuvers, instead of the rear of the car following the front smoothly, pushing out a bit, it suddenly "tucks in" and "grabs" throwing the balance off.
I was alerted to how bad it was when I had to make an emergency maneuver on the turnpike yesterday.
Some idiot in an SUV comes charging on from the on ramp. I'm in the middle lane and the blind ass keeps charging across the lanes right into the side of my car, so I have to swerve into the next lane to avoid a collision. It's something I've had to do before as I'm sure many of you have at one time or another. Sucks, but no big deal. You quickly move the car into the next lane. But with the new handling quirk, the rear tucks and grabs, and suddenly throws my car sideways at 65 mph! I try to keep calm and gently start counter-steering, but the car just flips the other way. I have to keep correcting back and forth until the chassis finally settles and corrects itself.
I'm not a panicky driver. The avoidance and corrections I made were very minor and done with a cool head.
I'm now very aware something is wrong here creating very unstable handling.
Any ideas why a simple alignment could so dramatically change the characteristics of the car? Or could it be the tires? (I sort of doubt it, but...)

[Beer]

Did you get a print out of the settings they used? Sounds like you could use a tad more rear tow in.

[Retroman1969]

Thanks for the reply!
I didn't, but I have never had such an issue, so I didn't think to ask for it.
It's hard to explain, but the rears had fairly extreme negative camber which quickly wore out rear tires. I had that "corrected" and they did a full alignment while at it. It's possible they got the toe settings off. Before all of this, it was as stable as a rock at any speed with any maneuver.
Now when steering the slightest bit off center at higher speeds, the car grabs so quickly and violently that it actually tries to slingshot itself in the opposite direction.

[KRAM36]

I pulled this from another thread. Maybe go back to the alignment shop and have them check the settings per the data sheet that Smallblock454 provided.

Originally Posted by Smallblock454

Hi,

take a look at the sheet i've attached. There you'll see the wheel align values. As you are livning in the UK, please use the clumn RoW Series for orientation.

It seems that they didn't adjust the camber on the left side. Maybe because you can't adjust camber on most older MB cars. Also it takes a lot longer to adjust everything to specs.

Over here in germany it is very important to adjust wheel alignment very correct, because the car is sensible at high speeds.

Regards Markus

[RedTele58]

I have the exact situation going on right now with my Aero car. I had all 4 sway bar links replaced and a 4 wheel alignment done right before I went to Hallett last weekend.

The car drove fine Sat, but somewhere between Sat and Sunday it developed the same characteristics - twitchy and unstable (the exact words I used to describe how it was acting). The front end felt like it was floating above 75mph, and I had the same tuck/grab get me sideways in a corner where I've never had a problem before. (I was chasing a GT3 pretty hard through the corner at the time, but I'm sure that had nothing to do with it. )

The car tracks straight down the road, but the steering wheel is sitting at the 1:00 o'clock position.

I too didn't get a read-out.

Did you take your car to your normal place, or did you use the guys I go to - just for comparison? (Don't want to name names, because both places are normally flawless in their work)

I'm bringing my car back in next week to get looked over and I'll be back at Hallett on the 30th, so hopefully it'll get figured out.

Let us know what you find out.

[Retroman1969]

Thank you for the readout Kram! I'll print that out and take it with me.
Interesting you're having the same character shift in your car after an alignment RedTele. I did take it to my usual place, and as you say, they're usually flawless in their work, but something went off here. I recall them saying they had trouble with the rear camber adjustment and couldn't quite get it to factory specs. I'm wondering now if they might have sacrificed toe settings in an attempt to get the camber in line. (honestly I don't know much about this stuff, just going off of what I've read and heard in my research)

[PaulDash]

Hey guys, great timing!

Just over a week ago (and was busy since), I got the car aligned. Around the city it feels fine, but when I took it to some nice twisty roads, I got scared. The car became, as you said, twitchy.

I was so concerned, last week I took it to another shop to check that everything was tightened down properly. It was.

Attached is the printout I got from them. Plus some translations so you don't have to learn Polish.

No I'm starting to think this is how the car is supposed to be. More direct. More raw. I like it!

[san rensho]

It could just be your tires. New tires are very squirmy because the tread blocks are very tall and the rubber is soft from the factory. After a few heat cycles, the tires firm up and handle better. when I got 4 new tires, my first ride out I thought I was on ice.

And by the way, wear on the inside rear tires is likely not from the negative camber in the rear. Its usually from too much toe.

[stephen wilson]

Doesn't Toe Out cause inside wear? There should always be some Toe In at the rear.

[thstone]

Could be the tires, but I'd guess that the tech messed up the rear toe alignment when he adjusted the rear camber. I'd take it back to the shop that did the alignment and have them check it. If its ok, then give the tires some miles to wear in and see if that helps.

[Retroman1969]

Looks like a consensus is forming.
I'll ask the shop to recheck the alignment with factory specs, especially the rear toe. I put about 700 miles a week on the car so any improvements related to the break in of the tires should creep up in a fairly short time. New tires didn't affect the handling feel of my weekender Boxster, but I've never had to have an alignment done on that car. It's possible in this case that it's a combination of the two.
Thank you guys so much for the input. I think you're on the right track.