I have a 2015 GT WITHOUT PP. Over uneven or slightly rough roads the back end of the car seems to hop side to side enough to scare me a bit at 60mph and above. This is on straight roads. Anyone else have this issue? Also, the shocks seem somehow too weak for the springs and weight of the car. I've driven lots of other cars, and this is the only one I've ever had that does this.

 

The stock IRS parts are weak and have soft rubber bushings which may cause wheel hop or unwanted deflection at high speed. You may want to look at aftermarket parts such as adjustable coilover springs, rear vertical links and rear toe links with better bushings, better differential bushings and subframe braces. All these parts will stiffen the rear end and improve the stock handling. Many of us S550 owners do go aftermarket for the same reason.

 

If your car is hopping around from side to side on a straight road I doubt the problem is wheel hop or soft bushings. You might want to start with tire pressure. But first how many miles are on the car? What is the alignment like?

Before anything else, make sure it's within specs as a stock car before you go down the road of buying the many aftermarket items that are advertised to make the car handle like a race car.

 

I love this forum, always someone to say I'm wrong after a comment. I think I will stop commenting for inducing so much false information into this forum. Sheeesh.

 

I would suggest you lighten up. Everyone expresses an opinion, and many people may disagree with them. That is what a forum is all about. The fact someone disagrees with you, does not mean your opinion was wrong.

As to the original question, we really need to now miles on the car and tires. Has an alignment ever been done? Since we have IRS, a four wheel alignment may have to be done. Start with the little things first.

 

While aftermarket parts and upgrades undoubtedly improve the handling in performance issues it's not recommended to start changing the stock setup unless you know what you need to change and why. The OP didn't seem to have an idea of what is causing his problem. That is why I suggested starting the diagnostic process.

And your comment isn't wrong, premature yes, but not wrong.

For what it's worth I have posted to this forum admitting I posted bad info before.