A widely used pit strategy in motorsports is undercut and overcut. As the change of tire compound is necessary for a race, it becomes crucial to choose the correct strategy and makeup positions without fighting wheel to wheel on the track. The underlying phenomenon in both of these strategies is maintaining the tire life and heating the tire to an optimum temperature to provide the necessary grip, also termed as the tire warmup in short. So, let's dive deep into what is an overcut and undercut and how it is executed.
It is essentially running long by preserving tires. It involves the chasing car, letting the car in the front pit first. While they are pitting, the chasing car builds up a gap between them hoping that they stay ahead even after they themselves pit. This strategy is executed best when the track temperatures are low or the track does not have heavy braking zones, making the tire warmup extremely difficult, resulting in an out lap that is a lot slower than ideal.
In Monaco GP 2021 - Sergio Perez and Sebastian Vettel both used the overcut to significant effect here as they leapfrogged themselves ahead of Hamilton and Pierre Gasly, with Perez running long and with a good enough race pace on old tires also to overcut Vettel. Sergio went from 8th to 4th in Monaco, which is a track where on-track overtakes are rare.
The undercut pit stop involves a chasing car pitting before the car in front, and then using the fresh tire advantage he now has to close the gap before the leading driver pits. The idea is that when the leading driver does pit and then rejoins, the chasing driver manages to overtake him. As can be seen in the picture alongside (Bars are representing lap times) that just by pitting a lap earlier, the purple driver is able to undercut the yellow driver due to the fresher tire compound successfully. This strategy works well on tracks with high tire degradation and quick tire warmup, so the long-running driver has worse lap times than the freshly pitted driver.
In French GP 2021, the undercuts worked very well, even to the extent that Max Verstappen(P2) took out 3.2 seconds from Lewis in P1 and overtook him for the lead just by pitting a lap earlier. Also, Daniel Ricciardo jumped Pierre Gasly and Carlos.