For TRF421X: 42391 Front Knuckle Arm - Tamiya 9803566  [9803566]

Overview of the TRF421X knuckle arm

This part is catalogued as Tamiya 9803566 and is associated with the 42391 TRF421X reference. It is supplied as a replacement front knuckle arm for 1/10 scale touring cars using the TRF421X steering geometry.

The knuckle serves as the pivot between steering inputs and the wheel hub, influencing static and dynamic alignment behaviours such as camber change and steering response. Replacing the knuckle is a typical maintenance or tuning action on TRF421X-based cars to restore worn items or try alternate steering characteristics.

To fit the knuckle arm, remove the wheel and hub carrier fasteners, detach the steering linkage and any retaining pins, install the new arm, then reassemble with correct torque values and secure clips or set screws. Verify smooth hub rotation and re-establish wheel alignment prior to running the car.

Practical tip: swapping the knuckle can change toe under compression and transient steering feel; make measured adjustments and perform progressive test runs. Also replace or service nearby parts such as bearings and screws if they show wear.