Week 3: The Stop#
What it costs and what you’re allowed
The question#
What does one stop cost after the whole in-lap and out-lap are counted, and which strategies still exist after Friday has returned six sets?
Two outputs:
- a measured two-lap pit loss with a 95% interval
- the complete legal one- and two-stop compound sequences for one remaining physical inventory
We price before we compare. Week 4 makes the candidates run.
The first four words#
- stop — here, a conventional pit stop: the car diverts through the pit lane and becomes stationary at its pit position before rejoining
- in-lap — the lap that ends in the pit lane
- out-lap — the lap that starts in the pit lane
- stint — a run of laps on one set of tyres
The in-lap and out-lap are not ordinary laps. They contain the diversion we are trying to price.
Five more before the ledger#
- compound — a tyre specification: hard, medium or soft in this case
- set — four allocated tyres, two front and two rear, used together (2026 Sporting Regulations, Issue 08, Article B6.2.2)
- Standard Format Competition — three practice sessions — Free Practice 1 (FP1), FP2 and FP3 — before Qualifying, which sets the Race grid; Q3 is its final segment (Issue 08, Articles B2.1.1 and B2.4)
- ICTT — In-Competition Tyre Testing; its allocation differs from this case (Issue 08, Articles B6.1.1 and B6.2.4)
- suspension — a temporary halt to the Race procedure; cars wait before a possible resumption (Issue 08, Article B5.14.4)
Allocation, use and electronic return are different operations (Issue 08, Articles B6.2.4, B6.3.2 and B6.4.2).
2.8 seconds is not the answer#
2.8 s is the stationary service time for synthetic stop A. It measures only the time stopped at the pit position.
Pit loss includes entry, constrained pit-lane travel, service, exit, and both abnormal laps. All timing values are SlopU synthetic scenario values.
Price the counterfactual#
For stop event (i):
loss_i = observed in-lap + observed out-lap - two expected no-stop laps
Synthetic stop A, seconds:
loss_A = 112.4 + 108.9 - 99.8 - 100.5
= 221.3 - 200.3
= 21.0 s
The generator supplies the expected clean-air laps. We do not fit tyre wear again, and we do not borrow a real pit-loss magnitude.
One difference becomes six observations#
| Synthetic stop | Observed in | Observed out | Expected 1 | Expected 2 | Loss |
|---|---|---|---|---|---|
| A | 112.4 | 108.9 | 99.8 | 100.5 | 21.0 |
| B | 112.8 | 109.1 | 100.1 | 100.4 | 21.4 |
| C | 113.0 | 109.3 | 100.2 | 100.3 | 21.8 |
| D | 113.2 | 109.4 | 100.2 | 100.2 | 22.2 |
| E | 113.4 | 109.7 | 100.3 | 100.2 | 22.6 |
| F | 113.7 | 109.8 | 100.4 | 100.1 | 23.0 |
All times are seconds from the SlopU synthetic archive. Each loss repeats the same subtraction as stop A.
The estimate, with its working#
Mean:
(21.0 + 21.4 + 21.8 + 22.2 + 22.6 + 23.0) / 6 = 22.0 s
The deviations from 22.0 are −1.0, −0.6, −0.2, 0.2, 0.6, 1.0; their squared
sum is 2.80.
sample SD = sqrt(2.80 / 5) = 0.748 s
SE = 0.748 / sqrt(6) = 0.305 s
With 5 degrees of freedom, t* = 2.571:
22.0 ± 2.571 × 0.305 = 22.0 ± 0.785 s
Mean pit loss: 22.0 s; 95% interval: 21.21 to 22.79 s.
All values are SlopU synthetic scenario values.
What the interval says#
The six archive observations vary. The interval reports uncertainty in their mean under the calculation we just made.
It does not establish pit loss at another circuit, under another pit-lane layout, or for every future stop. Those cases are outside this synthetic archive.
One event gave us 21.0 seconds. Six events gave us an estimate and enough variation to attach an interval.
The real starting allocation#
Standard Format Competition, no ICTT:
| Specification | Physical sets allocated |
|---|---|
| Hard | 2 |
| Medium | 3 |
| Soft | 8 |
| Dry total | 13 |
The same table allocates 5 intermediate and 2 wet sets. Alternative Format and Standard Format with ICTT use different numbers. The FIA and Tyre Supplier may also determine otherwise.
Source: 2026 Sporting Regulations, Issue 08, Article B6.2.4. A set is four tyres of one specification (Article B6.2.2).
Friday removes six dry sets#
For this Standard Format case:
- return 2 dry sets after FP1, 2 more after FP2, and 2 more after FP3
- protect one mandatory-Q3-specification set from use or return before Q3
- protect two mandatory-Race-specification sets from return before the Race; if two specifications are named, retain one set of each
These are Issue 08 Article B6.3.8 rules. The wet-or-cancelled-session conditions in that article do not activate in this synthetic dry Friday.
An electronic return must be followed by physical return before the next session. The supplier then publishes what remains available (Issue 08, Articles B6.4.2–B6.4.3). Returned is unavailable, even when unused.
SlopU’s synthetic Friday#
The physical IDs are scenario values. M2 and M3 are the two protected Race
sets; S8 is the protected Q3 set.
| Deadline | Synthetic running | Sets electronically returned |
|---|---|---|
| after FP1 | S1, 12 laps | S1 used; S2 unused |
| after FP2 | M1, 9 laps; S3, 6 laps | M1 used; S3 used |
| after FP3 | S4, 11 laps; S5, 7 laps | S4 used; S5 used |
Six returns satisfy Issue 08 Article B6.3.8. S2 proves why “allocated minus used” is the wrong inventory calculation: it left without running a lap.
Post-FP3 ledger#
| Compound | Set | Synthetic condition | Available after Friday? |
|---|---|---|---|
| Hard | H1 | new | yes |
| Hard | H2 | new | yes |
| Medium | M2 | new; Race-protected | yes |
| Medium | M3 | new; Race-protected | yes |
| Soft | S6 | new | yes |
| Soft | S7 | new | yes |
| Soft | S8 | new; Q3-protected | yes, not before Q3 |
The other six IDs were electronically returned and must be physically returned before the following session (Issue 08, Articles B6.3.8 and B6.4.2). Use and return are separate columns because they answer different questions.
The bounded Race inventory#
Synthetic qualifying update: SlopU reaches Q3, returns S8 after Qualifying to
satisfy Issue 08 Article B6.3.8, and marks S6 unavailable after damage. That
leaves H1, H2, M2, M3, S7 for the Race.
Synthetic event bulletin: medium is the mandatory Race specification. The FIA names up to two mandatory Race specifications before a competition (Issue 08, Article B6.1.2).
Bounded assumptions:
- the Race is dry: no intermediate or wet set is used
- the Race is uninterrupted: no suspension change
- enumerate one or two stops only; do not choose a stop lap
For this case, Article B6.3.6 requires at least two dry specifications, including medium.
How to enumerate without guessing#
A compound sequence names one compound per stint:
- one stop creates 2 stints, so sequences have length 2
- two stops create 3 stints, so sequences have length 3
Test candidates in this order:
- Does the sequence use at least two dry specifications?
- Does it include the synthetic mandatory Race specification, medium?
- Is every named compound still present in the physical ledger?
Questions 1–2 apply Issue 08 Article B6.3.6. Question 3 applies the synthetic Race inventory. No timing comparison belongs in this test.
Every legal one-stop sequence#
One stop means two stints:
| Legal sequences | Why they pass |
|---|---|
H → M, M → H | two specifications; medium included; sets exist |
M → S, S → M | two specifications; medium included; sets exist |
Rejected:
H → Suses two specifications but omits mandatory medium — Issue 08 Article B6.3.6M → Muses the mandatory specification but not two different dry specifications — the same article
The reverse orders fail for the same reasons.
Every legal two-stop sequence#
Two stops mean three stints. With H1, H2, M2, M3, S7, these 18 pass:
| Shape | Complete sequences |
|---|---|
| two M, one H | M-M-H, M-H-M, H-M-M |
| two M, one S | M-M-S, M-S-M, S-M-M |
| two H, one M | M-H-H, H-M-H, H-H-M |
| two S, one M | M-S-S, S-M-S, S-S-M |
| one of each | M-H-S, M-S-H, H-M-S, H-S-M, S-M-H, S-H-M |
Every row includes medium and another dry specification (Issue 08, Article B6.3.6). A used set is not thereby returned: this scenario permits S7 to be refitted. Sequences without M or with only one compound fail.
A tyre change is not always a stop#
During a suspension, changing wheels and tyres is permitted work (Issue 08, Article B5.14.4). If the car then leaves the pit lane on that set, the set counts as used (Issue 08, Article B6.3.2).
So a car can start on hard, change to mandatory medium during a suspension, and resume having used two dry specifications. The universal claim “a conventional stop is compulsory” is false. We do not price this exception.
The wet-tyre exception also matters: the two-dry-specification rule applies only when no intermediate or wet tyre was used. Otherwise non-compliance brings disqualification; if the Race is suspended and cannot restart, the sanction is 30 seconds (Issue 08, Article B6.3.6).
What passes forward#
Week 3 gives week 4:
- stop price: 22.0 s, 95% interval 21.21–22.79 s, from this synthetic archive
- legal candidates: 4 one-stop and 18 two-stop compound sequences under the synthetic bulletin, Race inventory and bounded assumptions
Week 4 makes those candidates run lap by lap and compares finishing time. It does not get to recover an illegal strategy by making it fast.
Assignment 1 separates the same two obligations: its measurement criterion asks for the estimate and uncertainty; its model-fitness criterion asks whether the strategy obeys the regulations.