Ferrari got a headstart with its title-challenging car for 2017, according to Mercedes boss Toto Wolff.
Mercedes won the last three drivers' and constructors' championships on the trot, but Ferrari's Sebastian Vettel is now 25 points clear in this year's chase, while the Italian team is leading Mercedes by 17.
"To our knowledge, Ferrari started development of its car very early - in December 2015. For us it was only March 2016," Wolff told newspaper Suddeutsche Zeitung.
"By then, Ferrari already had more than 50% of its resources on the new car.
"Ferrari has perhaps a 16-week lead, and in that time you can find downforce worth four or five tenths."
The season continues next weekend in Canada.
