Chaos Vehicle suspension constraints become permanently unstable after GeometryCollection fracture in same solver

SAS-DXB
Tue, 16 Dec 2025 01:42:19 +0000
World Creation

Engine Version: UE 5.7.1 (did not reproduce in 5.5)

Summary:
When a GeometryCollection fractures in the same Chaos solver as a Chaos Vehicle, the vehicle’s suspension constraints become unstable and remain unstable indefinitely, even after the fracture event completes. The instability only resolves when the GeometryCollection is removed from the solver.

Repro Steps:

1. Create a Chaos Wheeled Vehicle that uses suspension constraints OR use the matrix sample vehicle.

2. Add a GeometryCollection that fractures on impact (1.0 damage threshold).

3. Ensure the GeometryCollection use the default world Chaos solver.

4. Drive the vehicle and wait until the GeometryCollection fractures.

5. Observe suspension behavior.

Observed Result:

Suspension becomes unstable and remains broken indefinitely.

Suspension target positions remain valid and unchanged.

Removing the GeometryCollection immediately restores stable suspension.

Expected Result:

Fracture may cause a temporary disturbance, but suspension should recover.

GeometryCollection fracture should not permanently destabilize unrelated constraints.

Additional Notes:

Assigning the GeometryCollection to a separate ChaosSolverActor fully resolves the issue.

This is not related to wheel contact or traces.

Did not occur in UE 5.5, began appearing in later versions (Didn’t test 5.6).

Video:
https://youtu.be/nJrsGII7DqU

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