Tuned mass damper

A 9 kg disc suspended between two springs inside the nosecone, tuned to oscillate out of phase with the front suspension and keep the tyres in steadier contact with the road — stabilising the aerodynamic platform.

A sprung mass sealed inside the nose is not obviously "bodywork", so the immobility requirement was not obviously engaged.

Consistent front-end grip and a more stable aero platform over kerbs and bumps.

The FIA International Court of Appeal ruled on 22 August 2006 that the damper was bodywork failing to remain immobile relative to the sprung part of the car. Banned from the Turkish GP onward.

Mid-season, and in a title year. This is the clearest case of the "rigidly secured and immobile" sentence reaching something that is not visibly bodywork at all.