My car makes me seasick!

If a MB does not ride well for the poster I don’t think a CTS will be an improvement either, especially a used one. The brand new ones are great cars but previous generation scream cheap and have sub par motors unless you purchase the recent models.

Since this problem only occurs with weight in the rear I’d lean towards a tire issue (assuming the new ones went on the front) or a suspension issue (looseness in a trailing arm bushing, loose rear wheel bearing, strut/shock, etc, etc.)

It’s quite possible to have a totally defective strut or shock in which the bounce test doesn’t reveal much. Sometimes it just flat takes diassembly of the component and a “hands on” feel.
Based on the weight only issue, I tend to lean towards a strut or possibly a tire issue.

It’s quite possible for an aged tire, even with good tread, to cause something like this due to the rubber hardening with time. A tire that had great traction when the rubber was soft and pliable may lose most of that traction when the rubber hardens like week old bread.

The car is fine; it just has an undiagnosed glitch and many cars out there suffer from glitches no matter the make or model.
Hope that helps.

I just noticed that the OP never told us that this vehicle had AWD.
That assumption came from another forum member, and the OP never corrected or commented on that assumption. My research tells me that this is a RWD coupe, not an AWD vehicle.

That being said, I still think that, since the problem has existed ever since the OP bought this MB as a used vehicle, it is more likely to be a suspension issue than a tire issue. But, until the OP logs back in with more info, this is all just guesswork.

dpalmer5

How about the additional information that has been requested?

Actually, since it has been at least 10 days since the OP last logged onto this thread, I guess that we won’t get that additional information.

Dare to be dull.