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Step 7: Physics, PhysX to Chaos (physics)

UE5 replaced PhysX with Chaos. This step cleans up physics settings and moves PhysX vehicles to Chaos vehicles.

Done automatically​

  • .ini rules of the physics group: PhysX-era settings that nothing reads under Chaos are removed.
  • 4-wheel vehicles: vehicle and wheel Blueprints are re-parented to WheeledVehiclePawn and ChaosVehicleWheel, with their parameters mapped:
    • mass, drag, chassis size, input rates;
    • torque curve and max torque, RPM, moment of inertia;
    • gears, reverse, shift RPMs, differential, steering curve, wheel setups;
    • wheel radius, width, mass, steer angle, brakes, suspension travel, axle/steering/engine flags.
  • Function call, variable, cast and variable-type nodes that pointed at the PhysX vehicle classes are retargeted.

UEAPM ships load-only copies of the 4.27 PhysX vehicle types, so 4.27 vehicle assets load in 5.8 with all their data before being converted.

Reported for you​

  • Tuning parameters without a Chaos equivalent.
  • DestructibleMesh assets (use a Chaos Geometry Collection).
  • TireConfig assets (use wheel friction settings and physical materials).
  • Simple (non-mechanical) wheeled vehicles.

Rule tables​

The physics rules of config.json (10 rules) and physics.json (22 movement and 11 wheel parameters mapped; 20 movement and 7 wheel parameters reported as unmapped).

Examples​

Before (4.27)After (5.8)
bEnablePCM, PhysXTreeRebuildRate in [/Script/Engine.PhysicsSettings]removed (no effect under Chaos)
vehicle Blueprint based on WheeledVehiclere-parented to WheeledVehiclePawn
wheel Blueprint based on VehicleWheelre-parented to ChaosVehicleWheel
DestructibleMeshreported: Fracture mode, New > Geometry Collection

See the FAQ for what carries over for vehicles.