Valtteri Bottas’s final pitstop in the Bahrain Grand Prix featured a change of only three tyres because he returned to the set that picked up a puncture on the opening lap.
Bottas ran fourth at the beginning of the restarted Sakhir race but dropped to the back of the field when his Mercedes Formula 1 team noticed a slow puncture under the safety car, caused by debris that Bottas had not even noticed hitting.
Though the front-right tyre had not deflated the puncture meant he was forced to pit at the end of the second lap under the safety car and change from medium tyres to hards.
That left Bottas only one other set of usable mediums, which he switched to on lap 25 before making his final pitstop on lap 38.
Mercedes told him it would only be for three tyres and refitted the first set of mediums – as they were mostly unused – and left the old front-right on the car.
The front-right gun operator did appear to engage the wheelnut, likely to be either a precaution or to satisfy the pitstop technology as teams employ software that does not let the light go green unless all four wheelnuts have been successfully re-tightened.
It meant Bottas’s front-right tyre was 13 laps older than the others on his car for the final 19 laps of his race, but as Bahrain is a clockwise circuit the front-right is protected rather than the stressed tyre.
A three-tyre change is extremely rare. But it is entirely within the regulations, which do not govern how many tyres may be changed during a pitstop.
F1’s tyre rules require drivers to use at least two different specifications of dry compounds during the grand prix.
Using a tyres of different specifications at the same time is not allowed. A driver who ends up with a mix of compounds, e.g. softs on the front and mediums on the rear, must pit to change them for a matching set within three laps.
Mixing compounds is also not considered a valid satisfaction of the rules demanding two different specifications used during the race, either.