Undercut

How it works

A driver who pits earlier than a direct rival rejoins on fresh rubber while the rival is still circulating on worn tyres. Fresh tyres on most F1 compounds are typically one to two seconds per lap faster over their first few laps^[1]. If the gap on track is small enough, the fresher car closes it before the rival's own pit stop and emerges ahead when the rival rejoins.

Why it works on some tracks and not others

Two factors decide whether an undercut is viable on a given circuit:

• Tyre warm-up. The undercut only works if fresh tyres come up to working temperature quickly. On cold-surface circuits or with hard compounds, out-laps can be too slow to gain time, and the undercut becomes an overcut opportunity for the car staying out^[2].
• Pit lane delta. A long pit lane (Monaco is one of the slowest stops on the calendar) increases the time loss of stopping, raising the threshold at which an undercut pays back.

When teams call an undercut

• The car ahead is in clear air and the team can match its pace on fresh tyres.
• The driver has consistent pace on the relevant compound.
• The pit crew is set up for a clean stop in the next 1-2 laps.
• The team is confident the rival will not respond by pitting on the same lap (a "covering" stop neutralises the undercut).

Counter

The defensive response is to pit on the same lap as the attacker (covering the undercut) or to push hard on the existing stint to widen the gap enough that the undercut cannot reach. On tyres past their cliff, neither option works, and the attacker wins the position.