AMUS says Red Bull was heavier than Ferrari and has more power in reserve to further extend their advantage:
https://www.auto-motor-und-sport.de/for ... un-zeiten/
[quote]
Red Bull vs Ferrari. That was the conclusion after the test drives. This picture continued on the first day of practice for the Bahrain GP. However, Max Verstappen's lead is larger than it appears in the time table. According to team measurements, Red Bull has more reserves in terms of engine power and tank capacity.
The Red Bull's superiority was clearer in the long run than in one lap. "Max is in a league of his own," said Mercedes team boss Toto Wolff[/quote]