How Does the Undercut and Overcut Work in Race Strategy?
We often think that the success of a Formula 1 car during a race is down to its driver, horsepower or aerodynamics, yet strategy (under and overcut) can have a much more decisive impact on results. After all, it doesn’t matter how fast your car is, if a bad pitstop strategy puts you at the back of the field.
Race undercut and overcut strategy has played an even more important role over the last few decades, as teams and their technologies continue to evolve, the performance differentiators between cars reduces. With similar pace and performance on track, sometimes a good strategic call can be the only card teams can play to overtake the opposition.
Race strategy in the past
Before 2010, the regulations allowed refuelling, which meant the lap time difference between a near-empty car and a heavy, refuelled car was around 1.5s. Although the performance from a new set of tyres could reduce this deficit, it was difficult to overcome this penalty entirely. So, fuel became the dominant variable when establishing the optimum race strategy.
However, after refuelling was banned, tyre performance was once again the most important strategic factor. Consequently, teams focussed on managing tyre degradation to try and devise undercut and overcut scenarios to overtake their competitors.
Understanding tyre performance
To understand how undercuts and overcuts work, we first need to understand the behaviour of tyres.
The rubber used in today’s Formula 1 tyres is strongly influenced by temperature and hysteresis, so the lap time a car can achieve varies considerably depending on what stage of life the tyre is in.
There are essentially three main stages of tyre performance during a stint: warm-up, stabilisation and degradation. The amount of grip the tyre generates in each of these stages varies according to the stiffness of the compound (Soft, Medium or Hard). The graph below illustrates the typical lap time difference between a Soft, Medium and Hard compound throughout a stint.
- The Soft compound warms up the quickest and so has the fastest initial lap time. However, as the softer rubber begins to overheat and therefore wear, its performance drops off significantly towards the end of the stint.
- The Hard compound builds temperature more slowly and so takes longer to warm up which is why it is 0.5s slower than the Soft on lap 1. However, the harder compound is more resistant to overheating and suffers less wear, sustaining performance for longer and by lap 30 is 0.7s faster than the Soft.
- The Medium compound often sits between the Hard and Soft in terms of performance. Although, this compound can sometimes be difficult to warm up and is therefore much slower than both the Hard and Soft at the beginning of the stint.
The lap time difference between old and new tyres as well as the different compounds during the warm up (yellow) and degradation (purple) phases presents an opportunity for teams to either undercut or overcut their opposition.
What is an undercut?
There are three stages to a pitstop sequence; an inlap, a pitstop and an outlap. The total time lost or gained over this period relative to the opposition can lead to an overtake or being overtaken.
In the undercut scenario, Driver A (blue) pits first onto a new set of tyres, while Driver B (orange) stays out. Entering the pits, completing the pitstop and leaving the pits causes Driver A to lose a total pit loss time of around 20s. However, Driver A is now on fresh rubber which means they can complete a much faster outlap relative to Driver B who is on older rubber and completing a slow inlap. Driver B then pits, losing the same pit loss time of 20s. However, because Driver B stopped later, they effectively completed another lap on older, slower tyres, while Driver A was on newer, faster tyres. Consequently, Driver A undercuts Driver B and overtakes them.
The undercut typically comes into play on circuits with high tyre wear or thermal degradation. On this type of track, tyre warm up is not an issue, so switching to fresh rubber will always provide a performance advantage. However, there are additional factors that contribute to a successful undercut, not all of which are under the control of the team:
- A trouble-free pitstop and pitlane run
- Availability of a new or faster tyre set to fit during the pitstop
- A traffic-free window to drop back into after the stop
- The driver achieves the fastest possible in and out laps
- No yellow flags, safety cars or virtual safety car
What is an overcut?
An overcut on the other hand is where Driver B stops first, and Driver A stays out. After the pitstop, Driver B is much slower relative to Driver A.
This could be because Driver B has switched to a harder compound which takes longer to warm up, or Driver A has been told to push. After a few laps, this time difference means that when Driver A leaves the pits, they will come out ahead of Driver B, overcutting them.
Overcuts are usually common on low grip, low degradation tracks or during wet races. In these circumstances it can take several outlaps to get the tyres up to temperature. Overcuts can also occur when there is a strong car performance difference where the following car is simply much faster in free air once the car ahead pits.
An undercut in action
Overtaking the opposition during a race is a real triumph, however, the full outcome of a strategic undercut or overcut does not play out until the end of the race.
The 2021 Bahrain grand prix illustrates this nicely. The Sakhir layout is hard on the rear tyres and therefore presents a good opportunity for undercutting. Hamilton lost the lead to Verstappen on lap 1 and Mercedes changed their strategy immediately. At the first pitstop (1), Mercedes undercut the Red Bull by 4 laps which allowed Hamilton to overtake Verstappen on lap 18.
Hamilton was then able to build a 7s lead ahead of Verstappen and completed a second pitstop (2) on lap 28. However, to overcome the undercut, Red Bull decided to stretch Verstappen’s tyre life for another 11 laps to build a tyre age offset. Consequently, after his pitstop, Verstappen quickly catches Hamilton and battles for the lead. Although strategically Verstappen should have won, a failed pass left him in second place.
The power of an effective overcut
The tight streets of Monaco makes this Grand Prix dominated by traffic and tyre saving. Pitstops are undesirable as it is hard even for a fast car with a tyre advantage to make its way through the pack.
In 2021, a poor grid position left Hamilton following Gasly during the first stint. Running out of tyre life, Hamilton triggers the first pitstop phase (1), but Gasly stays out for one more lap, effectively overcutting Hamilton to stay ahead in the slower Alpha Tauri.
Vettel stays out a further lap and overcuts both Hamilton and Gasly, while Perez with a large car performance advantage, stays out for two more laps (2) and overcuts all three drivers. This manoeuvre jumps Perez from 5s behind Hamilton to over 5s ahead. In the end, Hamilton never passes Gasly, eventually stopping for a fastest lap attempt (3) on lap 66.
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Article written by: Gemma Hatton