McLaren have identified the cause of Stoffel Vandoorne's MCL32 feeling like a 'rally car' in last Sunday's Abu Dhabi Grand Prix.
The Belgian complained early on about his car's bizarre handling, telling his team over the radio that it felt like a 'rally car'.
Vandoorne made it to the checkered flag after a difficult race, ending his season with a P12 finish.
"We think that Stoffel spent the whole race with a large piece of tape stuck in the diffuser," Vandoorne's engineer Tom Stallard told Motorsport.com.
"The kind of super-sticky two-inch tape that touring car teams use to reattach the front bumper. At the end of the race there was a 20cm piece still stuck to the left hand diffuser fence."
The foreign piece of tape undoubtedly unsettled the car's balance in terms of downforce.
"During the race we believe this tape was much larger. We measured a loss of downforce equivalent to opening the DRS, but all around the lap, and without the drag drop," added Stallard.
"Around lap 22 the diffuser partially recovered and Stoff's pace improved. We think until this point it was caught on both sides, but then snapped and was then only on the left.
"I would guess the original piece must have been around 50cm long."
Toro Rosso's Pierre Gasly corroborated McLaren's thesis, telling the team after the race that he could see "something flapping" in the McLaren's diffuser.
Taking the impediment into account, Stallard believes Vandoorne did a great job keeping it all together.
"Given this I think Stoffel did an extraordinary job in not only keeping his car on the track, but also in keeping six cars behind him."