Some of the changes implemented to Project Cars with patch 4.0 is ability to force default setups in multiplayer portion of the game, enhanced brake assistance, additional best line visualisation, improved AI mechanics during pit stop and many other things. (gamepur.com)
McLaren P1 GTR — Updated the differentials for Stable, and Loose default setups, for more stability and ease of driving. (gtplanet.net)
Fixed an exploit where some players could load custom setups in Community Events when Default Setups are enabled. (gtplanet.net)