On the penultimate lap of the Mexico City Grand Prix on 1 November, 500 metres down the main straight, Lewis Hamilton was doing 349 kph with Overtake and a tow, and Max Verstappen, ahead of him, 338, according to the telemetry traces in Jon Noble's explainer for The Race. Worked out from the power curves printed in the 2026 rules, and assuming Verstappen was not using Overtake, Hamilton's 11 kph advantage left him a ceiling only 10 kW above Verstappen's: a computed limit, not measured deployment. Hamilton finished second, 0.799 seconds behind.
The limit is Article C5.2.8 of the 2026 Technical Regulations, which cuts how much electrical power the ERS-K may send to the wheels as a car's speed rises. Without Overtake, full deployment of 350 kW ends at 290 kph and power reaches zero at 345. With it, full power lasts to 337.5 kph and runs out at 355. Lando Norris, quoted by The Race, described the effect from the cockpit: "You literally have a limiter that stops you from going over a speed," he said, adding, "It kind of ruins racing."
Section C, Issue 21, which the FIA dated 19 October, writes the limit as straight lines on page C64. With Overtake not active, the limit in kW is 1800 minus 5 times the car's speed in kph below 340 kph, then 6900 minus 20 times speed from 340 kph up to 345, and zero from 345. With Overtake active, it is up to 7100 minus 20 times speed below 355 kph, and zero from 355. Article C5.2.7, one line above, caps the ERS-K's absolute DC power at 350 kW, a ceiling that applies on top of every line.
Setting each line equal to the 350 kW cap gives the two break points. A car without Overtake keeps full deployment only up to 290 kph (1800 minus 1,450 is 350) and is down to 100 kW at 340. A car with Overtake keeps 350 kW up to 337.5 kph (7100 minus 6,750 is 350), then tapers along a steeper line until nothing is left at 355.
Overtake's margin changes along the straight. Compared at the same speed, the extra power it allows is nothing at 290 kph and 150 kW at 320. It peaks at 337.5 kph, where the Overtake car may use 350 kW against 112.5 for the car without it. Past that point the Overtake line falls four times as steeply as the other one. The margin is 200 kW at 340 (300 against 100), stays at 200 kW up to 345, where the car without Overtake reaches zero, then halves to 100 kW at 350 and is gone at 355.
The Race's traces put Mexico's main straight on those lines. On the same lap, at 900 metres, Verstappen was doing 342 kph and Hamilton 350. The Race's account of why Mexico was hit so hard: the stadium section at the end of the lap sends cars onto the long straight with energy in hand, so they reach the taper early instead of only near its end.
At 500 metres the formulas cap Verstappen, at 338 kph without Overtake, at 110 kW, and Hamilton, at 349 with it, at 120 kW. At 900 metres the caps were 60 kW and 100 kW, with the gap in speed down to 8 kph. Those are the limits the printed curve allows at those speeds, assuming Verstappen, in the lead, ran without Overtake. They are not measured deployment, which also depends on how much energy each car had left.
Above 337.5 kph, each kph Hamilton gained cost him 20 kW. Verstappen gave up 5 kW for each kph below 340 and 20 kW for each above it, so by the 900-metre mark both cars were on the same slope. The Race's account is that the gaps froze once cars reached the taper.
Hamilton blamed the same setting in the post-race press conference, as RaceFans reported: "The engine can go faster, it's just they have these silly clips. It's the worst engine profile setting that I think they've probably ever had in this sport and it doesn't provide great racing." He also pointed to Mexico's thin air and its fast last corner as reasons the circuit is hard to follow on.
Article B7.2.1(b) of the Sporting Regulations, Issue 09, dated 1 October, lets the FIA change those curves circuit by circuit. At least four weeks before each event it sends teams any adjustment to the speed curves with and without Overtake, made only where needed to keep top speed compatible with the circuit's design and construction. Any Mexico City adjustment sits in that pre-event information rather than in the published rule books, so the numbers in this piece use the curve as printed in Section C, which is also what The Race worked from.
Clause (iii) of C5.2.8 adds a third curve. In the race or sprint, on specified circuit sectors during any power-limited period, deployment is held to 250 kW below 310 kph and then joins the line for a car without Overtake. The two meet exactly, since 1800 minus 1,550 is 250. Neither rule book lists those sectors: item (xii) of B7.2.1(b) has the FIA name them for each circuit in the same pre-event information. Clause (iv) sends low-grip conditions to a separate FIA document, FIA-F1-DOC-111.
The Race reports that the speed limit has been deleted from the 2027 regulations because more fuel flow, more boost and a larger harvesting allowance leave the cars less short of energy, though some speed-based restrictions stay for certain track sectors. The 2027 Technical Regulations, Issue 04 of 19 October, are published as a marked-up text, and their Article C5.2.8 carries flat figures on page C71: 350 kW with Overtake active in the race or sprint, 300 kW without it, and 250 kW on specified sectors during power-limited periods.
Four Grands Prix remain under the 2026 lines, starting at Interlagos on Sunday 8 November, where the cars run either the printed curve or whatever adjustment the FIA has already sent the teams for that circuit.