Water-cooled brake ballast tank

A roughly 26 litre tank of water, nominally for brake cooling, dumped overboard in the opening laps so the car ran far below the 580 kg minimum, then refilled in the pit lane before post-race scrutineering.

Minimum weight was checked after the race, and the rules permitted replenishment of fluids consumed during the race before weighing. The loophole is entirely about when the measurement happens.

Running tens of kilos underweight for most of the race distance.

Piquet and Rosberg disqualified from the Brazilian GP; the FIA Appeals Tribunal upheld the disqualifications roughly seven weeks later. Ballast tanks outlawed.

The political fallout escalated the FISA-FOCA war and the FOCA teams boycotted San Marino two races later. A technical loophole that moved the sport's governance.