i30N instability at 110–130 km/h after tire change suspension work – rear unsettled, help needed

[FF1991]

Hi everyone,
I’m looking for some advice regarding my Hyundai i30N Performance (280hp).

Mileage: ~68,700 km
Background:

• Bought the car at ~50,000 km – completely stable
• After switching to Continental SportContact 7 tires around ~60,000km, I started noticing instability around 120–130 km/h (car felt less planted)

A mechanic then installed Whiteline camber plates to improve stability which worked at the time.

Suspension history:

• Around ~65,000 km → front dampers failed and were replaced under warranty (OEM)
• A few thousand km later (~68,000 km) → issue returned
• Hyundai diagnosed camber plates as the cause of premature failure (~3,000 km use)

Second intervention (paid):

• Camber plates removed → reverted to OEM top mounts
• Replaced:
  • Front struts (LH + RH, OEM)
  • Front springs
  • Bump stops + dust boots
  • Strut bearings
  • All associated hardware
• Alignment made

Current issue:

After all this work, the car is still unstable at higher speeds (110–130 km/h).

• In medium/high-speed corners:
  • Rear feels unsettled / not planted
  • Small repeated lateral corrections (“wiggle”)
  • Feels like slight rear-end yaw oscillation
• Issue was also confirmed by the workshop manager during a test drive

Additional info:

• Alignment values reportedly outside OEM spec, but symmetrical left-to-right (dealer claims this is acceptable)
• Rear suspension (dampers, etc.) still original (~68k km)

Questions:

1. Could rear alignment being outside spec (even if symmetrical) cause this instability?
2. Could worn rear dampers cause this kind of high-speed oscillation?
3. Any known sensitivity of the i30N to rear toe settings?
4. Anything else worth checking (rear bushings, subframe alignment, etc.)?

I really like the car, but in its current state it doesn’t feel safe at higher speeds.
Any input or similar experiences would be greatly appreciated, I'm really lost here.
Thanks in advance.

 

[Bu11eT]

Alignment values reportedly outside OEM spec, but symmetrical left-to-right (dealer claims this is acceptable)

was this before or after the alignment was made?

The i30N is known for being a bit sensitive at the rear.
There are aftermarket solutions for it, e.g. Whiteline Anti-Roll-Kits which should make the car feel way more planted during light, higher-speed cornering, e.g. on the motorway.

Maybe its worth going on a driver with another i30N to get a feeling for how worse off your car is in this regard?

 

[FF1991]

was this before or after the alignment was made?

The i30N is known for being a bit sensitive at the rear.
There are aftermarket solutions for it, e.g. Whiteline Anti-Roll-Kits which should make the car feel way more planted during light, higher-speed cornering, e.g. on the motorway.

Maybe its worth going on a driver with another i30N to get a feeling for how worse off your car is in this regard?

Hello,
Thanks for your reply.
No, when I bought the car it was fine. After changing the tires I noticed wobbly in the rear, after the camber plates it was fine but I Guess the camber plates messed up with the shocks so they took them out. But now, without them, the car feels so unstable when cornering around 110-120km/h that it doesn't feel safe.
I don't know anyone with the I30N to have a comparison. Even the office shop which is official representantive of Hyundai said they don't normally have these cars.
I appreciate any input here so I can at least point them to a possible cause and solution.