Specifically, as reported by motorsport.com, the new rules focus mainly on engines, tires, turbos and aerodynamic devices. The number of engine seals allowed goes from three to two for 2018, plus the number of turbochargers is cut almost in half, from six down to four.
FIA also took note of the amount and type of tires teams were using. Unregistered tires will no longer be allowed for practice and warm-ups, but teams will be allowed to register up to 20 tires over the course of the season.
Teams will also have to declare their transmissions and rear-wing aerodynamics specifications at the start of the season, and those specs will then essentially be locked for the year. This follows issues with teams making changes during last season.