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The undercut explained
Pitting before your rival to pass him on fresh tyres: that is the undercut. Enter the gap, how much faster new tyres are and how many laps the other car stays out.
You gain 0.7 s, not enough to clear a 1.5 s gap. You would need 2 laps of the rival staying out.
The gap, lap by lap
you aheadyou behind
- Before your stop+1.5
- Lap 1 on new tyres+0.8
- After the rival stops+0.8
The arithmetic
Both cars lose the same time driving through the pit lane, so it cancels out. What counts: gap after = gap before - (laps x tyre advantage) + out-lap loss - difference in the stop.
Here: 1.5 - (1 x 1.2) + 0.5 - 0.0 = 0.8 s.
A simplified model: real races add traffic, fuel and tyre wear that changes lap by lap.
The undercut in three steps
- You stop firstYou pit one or more laps before the car ahead.
- Fresh tyresWhile the rival stays out on worn tyres, you lap faster and close in.
- Rival stopsWhen he pits, both lose the same in the pit lane. If you gained more than the gap, you come out ahead.
The math
Gap after = gap − laps × tyre advantage + out-lap loss
Example: a 1.5 s gap, tyres 1.2 s faster per lap, 0.5 s lost on the out-lap: one lap gives 0.7 s, not enough. Two laps give 1.9 s: enough.
Undercut and overcut
Undercut
- You stop earlier
- Works when new tyres are quick right away
- Uses the rival's worn tyres
Overcut
- You stop later
- Works when new tyres take time to warm up
- Wins while the rival loses time on his out-lap
More F1
Questions
What is the undercut in F1?
Pitting before the car ahead to use the fresh tyres and come out in front of him once he stops.
Why does the pit-lane time not count?
Because both cars lose it: the one stopping first and the one stopping later. What decides it is what you gain on track between the two stops. If one stop is slower, that difference does count: the calculator adds it.