The W12 was powered by the Mercedes-AMG M121 — a 1.6-litre turbocharged V6 hybrid producing over 1,050 bhp (782 kW) with 530 lb-ft (718 Nm) of torque and a 13,000 rpm limit. The car's dry weight was 833 kg (1,836 lbs), rising to 943 kg (2,078 lbs) with driver and fuel. Its dimensions were 5,700 mm in length, 2,000 mm in width, and 3,724 mm wheelbase. Front suspension was double wishbone pushrod; rear was double wishbone pullrod.
The W12 was developed as successor to the dominant W11, which had won all but four races in 2020. It raced under regulation changes that reduced floor-area downforce, a modification that commentators suggested disadvantaged low-rake designs such as the Mercedes relative to higher-rake competitors. The DAS dual-axis steering system used on the W11 was banned for 2021.
The car won in Bahrain on its debut and took victories in three of its first four starts. Hamilton reached his 100th career Grand Prix victory at the Russian Grand Prix in rain-affected closing laps, and claimed his 100th pole position at the Spanish Grand Prix. The W12 secured Mercedes' eighth consecutive Constructors' Championship, but Hamilton lost the Drivers' title to Max Verstappen following a controversial season-closing decision at the Abu Dhabi Grand Prix. Bottas won the Turkish Grand Prix. Hamilton recovered from a São Paulo Grand Prix disqualification to win that race.
On iRacing, the W12 is a purchasable car with a detailed setup manual. The sim car replicates the real car's hybrid system architecture: the MGU-K deploy mode can be set to one of five states per lap — No Deploy, Qual, Attack, Balanced, and Build — and is limited to four mode changes per lap. No Deploy and Qual modes are available only in Practice and Qualifying sessions; Attack, Balanced, and Build are available in Practice and Race sessions.
The digital steering-wheel dash displays two pages: a warmup page showing speed, tyre surface and carcass temperatures, current gear, battery charge, deploy mode, water temperature, brake bias, and a lap delta; and a race page that swaps tyre data for fuel consumption information, showing fuel used per lap, target fuel usage, remaining laps of fuel, and a coloured fuel bar (green blocks for surplus, red for deficit, each block representing 50 grams).
Three tyre compounds are available in the sim — Soft (red sidewall lettering), Medium (yellow), and Hard (white). Cars must start any race on the compound used in qualifying. Three aerodynamic downforce packages are available: High, Medium, and Low. An aero calculator in the garage estimates front downforce balance and downforce-to-drag ratio based on ride-height inputs from telemetry.
The chassis setup system exposes front and rear heave spring rates — which resist vertical travel and are critical to maintaining aerodynamic platform stability at speed — alongside roll rates, camber, toe, and corner weights for all four corners. Differential settings cover entry, middle, and high-speed locking torque, each adjustable from the cockpit via an in-car F8 black-box menu. Brake bias and brake migration (forward shift under heavy pedal application) are also adjustable in-car.
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