Mercedes swapped their new bodywork on Lewis Hamilton's car during third practice for the German Grand Prix, abandoning an upgrade brought to Hockenheim.
The Silver Arrows brought redesigned bodywork for the race as temperatures were expected to soar.
It was hoped that opening up more of the car would prevent Mercedes from struggling in the heat as they had done in Austria recently, and Hamilton was able to hang onto Ferrari in scorching heat during Friday practice.
However, Saturday arrived with temperatures dropping sharply, as much as 15 degrees Celsius.
Hamilton's initial laps were comfortably slower than Ferrari's, prompting Mercedes into action as Hamilton's car had its slimmer bodywork fitted in the search for extra speed.