Off-throttle exhaust-blown diffuser

Engine mapping that kept exhaust gases flowing over the diffuser even when the driver was off the throttle, sustaining rear downforce through the corner rather than only under power.

Engine mapping was unregulated and exhaust exit position was free.

Large and concentrated in high-speed corners.

Chaotically. Banned, repealed, then "extreme" qualifying maps banned at Valencia, throttle behaviour restricted at Silverstone, then all restrictions abandoned for the rest of the season. Structurally closed in 2012 by mandating a high exhaust exit.

The worst single case of mid-season regulatory whiplash in the modern era, and the strongest argument for the register recording effective dates rather than seasons.