How Formula 1 practice rules allow teams to split car specifications

Testing parts during official practice

Formula 1 regulations give teams freedom during free practice sessions to evaluate different aerodynamic or mechanical specifications across their two entries. In the United States GP: Audi evaluated a new upgrade package by outfitting just one car for the opening session while maintaining the previous specification on the second, allowing their technical staff to gather comparative running data.

Rules governing mid-weekend specification changes

Teams are permitted under the sporting regulations to alter bodywork and setup components between practice sessions, meaning a team can switch a car over to a newly tested package ahead of subsequent running. Once qualifying begins, however, cars enter parc ferme conditions, where the technical rules strictly limit component changes and require cars to run in a fixed configuration.

Official reference: FIA's Friday press conference on 23 October.