What single development item do you think made the most difference to a team's performance in 2015?
Dan Sainsbury, via email
Unusually for a Formula 1 season, there was no big new system thought up that everyone else needed to copy. So it was very much a year of teams converging on similar concepts.
F1 2015: The political year in review
Formula 1 too focused on protecting small teams - Fernando Alonso