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Undercut Threat

F1 Chief Technical Engineer Rob Smedley helps break down each of the new F1 Insights powered by AWS in a series of blogs during the 2021 Formula 1 season

A Blog by Rob Smedley

One of the most fascinating parts of an F1 Grand Prix race is when two teams are locked in battle, bumper to tail and just about to enter the pit stop window (the time of the race when it is predicted to make pit stops for a change of tyres). When the cars are travelling in close proximity, it is often a case of who blinks first and as we've seen in so many occasions, the brave can very often vanquish less decisive opponent.

The situation is only heightened when the two cars are in what we call, undercut proximity. At this point there is a clear possibility of the strategists being able to affect the outcome of the race. Having sat on a pit wall on many occasions and being either the car in front that is going to have to defend from an undercut or the car behind who has the chance of gaining positions and in some cases even winning the race, I can tell you that this is one of the most exciting parts of a Formula One Grand Prix.

The New Graphic – Undercut Threat

To explain this new F1 insight it is important to first explain the background of it and in doing so explain exactly what is meant by an undercut.

During an F1 race, there are certain periods where pit stops should be affected in order to gain the best outcome for the particular driver or team. These periods span across several laps, say 5 to 6, and are more commonly known as pit stop windows. When two cars are running in close proximity to each other within the pit stop window, the following car has the opportunity to pass the car in front during the series of oncoming pit stops with what is known as an undercut.

The premise is reasonably simple, prior to the pit stops the two cars will have a certain amount of tyre degradation which will make them run slower than the scenario where they had new tyres fitted. If the following car of the pair was to pit first this would allow that car to be able to run at least one lap on the freshly fitted and crucially, faster tyre set than the car that had stayed out. If the lap time advantage of the new tyres versus the degraded tyres was bigger than the gap between the two cars prior to the pit stops then the car that was second will come out in front after the round of pitstops.
There are lots of assumptions in the simplistic scenario given above, but in absolute basic terms this explains the undercut. This is well represented by the F1 AWS Insight that is known as Pit Strategy Battle. This insight is used extensively during the pit stops to inform us fans as to whether a car will successfully make or defend from an undercut.

The new graphic will help explain which cars are at threat from undercut (or more positively which cars have the possibility of making an undercut). This will help to bring the fan further into the world of the F1 strategist, where split second decisions need to be made. This is undoubtedly one of the most tense moments that the technical team have to face during the race; get it right and you will have helped your team to get more points, get it wrong then you've had a bad Sunday afternoon. The fan is now able to live that tension through this new graphic.

The Modelling

The model represents two cars:
"A=car in front"
"B=car behind"

We need to understand the following:
• The difference between the compounds’ pace
• The different between the compounds degradation
• The difference between the drivers pace

The model is represented here below:
TM+1A ≥ TM+1B

TM+1A ≥ TMB + LTB (^) + PL
TMA + LTA(e) + PL ≥ TMA + GMAB + PL + LTB (^)
LTA (e-^) + D ≥ GMAB + LTB (^)

LTA (^) + DA.e ≥ GMAB + LTB (^)
PA + PsTA + DA.e ≥ GMAB + PB + PsTB

GMAB ≤ (PA – PB) + (PsTA – PsTB) + DA.e

GMAB: Gap between A, B in lap M
PA – PB: Delta pace of the cars
PsTA – PsTB: Delta pace of the tyre compound wrt soft
DA: Degradation of the A car’s tyres

We can add the time lost on traffic for undercutting cars TB
GMAB ≤ (PA – PB) + (PSTA – PSTB) + DA.e + TB
Of course, all these get under operator E [.] (evaluator). 


This is another F1 AWS insight that offers us a more engaging F1 race as it enables a fan to go further behind the scenes. The insight delves into the world of strategy and demonstrates just how much work is going on behind the scenes. Constantly. We are now at the stage where we can start to piece together whole sections of a Grand Prix, through the use of the graphics. Here we can highlight who is at threat from an undercut and then use Pit Battle Forecast to tell us if the undercut is going to be successful or not once the particular team has rolled the dice. With each insight introduction we are explaining the intricacies of F1, bit by bit.


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