Changes to regulations for the season, which mandated the use of turbo-hybrid engines, contributed to the start of a highly successful era for Hamilton. That year saw Mercedes win 16 of the 19 races that season, 11 of those secured by Hamilton as he prevailed in a season-long duel for the title against teammate Rosberg. Clinching his second drivers' title, and eclipsing the victory tally of all British drivers before him, Hamilton declared over team-radio after the final race in Abu Dhabi: "This is the greatest day of my life." New driver number regulations brought in for 2014 allowed drivers to pick a unique car number to use for their entire career, and so Hamilton elected to drive under his old karting No. 44 for the remainder of his career.