A double stack is when a Formula 1 team brings both of its cars into the pits one immediately after the other during the same lap.
Each F1 team operates two cars but normally has only one pit box and one pit crew carrying out tyre changes. This means the second car has to wait until the first car’s pit stop has been completed before its own stop can begin.
Why do teams double stack?
Teams generally prefer to leave a gap between their cars’ pit stops, but sometimes both drivers need new tyres at the same time.
This is particularly common when there is a sudden change in conditions, such as rain arriving, or when a Safety Car gives drivers an opportunity to make a pit stop while losing less time relative to cars remaining on track.
In these situations, leaving one driver out for another lap could cost more time than having them briefly wait behind their teammate.
What is the risk?
Timing is crucial.
If the first car’s pit stop is completed before the second arrives, both stops can be carried out with relatively little delay.
But if the second car arrives too soon, it may have to sit behind its teammate while the mechanics finish servicing the first car. This waiting time can cost positions.
Teams therefore have to consider the gap between their two drivers before deciding whether a double stack is worthwhile.
Example: The team double stacked its drivers under the Safety Car.
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