car steers/jerks to one side going over 'ridges' in the rode
 

First off, history of the tires on My06. I was running Conti DWS all-around (DD) but staggered. Then I got a nail in the rear passenger so they replaced it with the PS A/S 3+ since they didn't make/carry the DWS anymore. Rear driver tire was naked so we placed that with a PS A/S 3+. So 3-4 year old DWS in the front and 1 year old PS A/S 3+ on the rear passenger side and about 1 month on the driver rear PS A/S 3+.

I know how this car is with matching tires but any time I'm on the highway and I drive on top of a seam that connects two sections of highway together, My06 will want to turn right. And it's a sharp right at that. Like it wants to go head first into the car in the next lane. I obviously correct it, as I'm pretty much used to it. But it has never been this bad. Previously, driving on the split sections, it felt more like a push to off of the ridge/split section (whatever you want to call it, but you know what I mean) as opposed to the steering wheel twisting in my hand and forcibly moving off and away from the ridge. It's only on these types of bumps that are parallel to the tire that causes the car to be possessed. Everything else is fine. Turning 90 degrees at 40-50mph is great. Wet traction is good besides the sensation of floating on occasion during misty conditions.I thought I read somewhere about putting in stiffer bushings to alleviate the issues but I wasn't too sure.

Any thoughts?

Not sure why you decided to mix different tire types/grades. But ya did. :) Our cars are tire and tire pressure sensitive and running different brand/pattern/age tires makes guesses difficult. The Continentals have an asymmetric tread pattern -- the word "Outside" is embossed on the sidewall. I think the Michelins asymmetric as well. Can you read "Outside" on all the tires? It will make a handling difference if they're inside out as does the different tread patterns. Continental Extremecontact DWS 06 tires are readily available for about $25/tire less than the Michelins. Any tire shop can get them.

-- Chuck

Agreed, you need to get a matching set of tires and insure even tire pressure first in the troubleshooting process here.

More than the mismatched front vs rear, I believe your issue is mismatched diameters on the rear. They aren't same age or miles, weren't from the same manufactured batch.

We know our cars are hypersensitive to rear tire pressure. Well all that does is make one rear a different diameter than the other. Our rear diff hates different rear diameters.

So your mismatched rear tire diameters are doing the same thing mismatched pressures do, only much worse.

There have been reports of people buying brand new tires, and one rear was simply made from a different manufacturing batch than the other, and this was enough to cause mismatched rear steering issues. Getting Tire Rack to replace one of the rears so they were matching manufacturing batch cured it.
You are dealing with not only different batch, but different wear.

Lets prove this is the issue. Rotate left and right rear tires. See if issue steers the opposite direction.

The fix is a matching set of rear tires. Since you are running AS, I'm gonna assume you aren't going to buy a pair of new rear tires (if you really cared yu wouldn't be running AS on this car). So experiment with tires pressures. Lets assume the older rear is the smaller one. Bump up the psi in that tire one psi at a time, until issue minimizes. If it starts switching direction again, drop back one psi and call it good as its gonna get.

Next time you need one new rear, buy a pair.