The Benetton Group acquired Toleman in October 1985. The team's structure remained largely unchanged: Peter Collins continued as team manager and Rory Byrne as chief engineer. The planned 1986 chassis — originally designated the Toleman TG186 — was simply renamed the B186. The team remained based at its Witney headquarters in England.
The key change was the engine supply. BMW replaced the privateer Hart 415T units that had powered Toleman's cars since the team's 1981 Formula One debut. BMW's focus for 1986 was the new "lay-down" version of its M12/13 engine, developed for the revolutionary Brabham BT55; the standard "upright" version was supplied to Benetton and Arrows. Because both the M12/13 and the Hart used an inline-four configuration with similar turbo and exhaust layouts, only modest adjustments were required relative to the Toleman TG185. The B186 was also the only Benetton F1 car powered by BMW engines and the only one supplied with Pirelli tyres until the B190B in 1991.
With the engine deal finalised only in the last week of October 1985, Byrne had little time before the season-opening race on 23 March in Brazil. Three chassis were nonetheless completed in time for that round; four more were finished during the season, for seven chassis in total. Carbon fibre monocoques had by that point become standard practice in Formula One. Chassis 4 was written off by Fabi in a practice crash at the Canadian Grand Prix; chassis 7 was the race-winning car at the Mexican Grand Prix.
The chassis was refined over the TG185 — sidepods were reshaped for greater aerodynamic downforce, and the structure was made considerably stronger to handle roughly 600 hp more than the Hart had produced in qualifying and roughly 200 hp more in race trim. A particular design challenge was accommodating the B186's two very differently sized drivers: the 1.68 m Fabi and the 1.83 m Berger.
The livery reflected the new ownership. Benetton green and markings from sponsors Sisley and Riello covered the front and sidepods, while the engine cover carried multi-coloured streaks on white — representing the Benetton Group's "United Colors of Benetton" brand. At the Detroit Grand Prix, both cars ran tyres with multi-coloured sidewalls. Each car displayed the flag of the host nation beside the rear-view mirrors, except at San Marino where both cars flew the San Marino flag despite the Imola circuit being located in Italy.
The BMW M12/13 supplied to Benetton produced approximately 50 hp more than the official factory units given to Brabham, made possible by modified engine management chips. This arrangement came to a head at the Austrian Grand Prix, when Paul Rosche of BMW demanded to inspect the chips; the team had retained the originals and was able to produce them, avoiding a breach of contract.
Early in the season the B186 struggled with the engine's "light switch" power delivery, and reliability was compromised by a shortage of spare parts. The car was also less competitive on slow circuits where turbo lag of the four-cylinder unit made it slower off slow corners than the V6 turbos of Honda, TAG, Ferrari, and Renault. Pirelli's tyres initially lagged behind Goodyear — Pirelli had little data of its own, relying mainly on results from the Ligier team running Renault V6 engines.
By mid-season, once the spare-parts situation was secured, a comprehensive development package was introduced: revised front and rear wings, a new underbody, new suspension, and a further-strengthened chassis. A new rear wing design arrived at the Austrian Grand Prix, where the combination of improvements and the high-speed Österreichring made the B186 the fastest car in the field — Fabi and Berger occupied the front row of the grid.
Berger set the highest top speed of the 1986 season at Monza: 351.22 km/h (218.24 mph) during the second qualifying session at the Italian Grand Prix. This stands as the second-fastest speed recorded in the original turbo era of Formula One (1977–1988), exceeded only by Nelson Piquet's actively suspended Williams-Honda which reached 352.135 km/h at Monza in qualifying for the 1987 race. Fabi was second-quickest on that same straight at 349.85 km/h.
The B186 finished in the points at each of the first three races, including a podium for Berger at the San Marino Grand Prix. The car's season total was nine retirements from 32 starts. It was most competitive at the five high-speed circuits on the calendar — Imola, Spa, Hockenheim, Monza, and the Österreichring — where straight-line speed and high-speed cornering ability played to the BMW engine's strengths.
The Austrian Grand Prix illustrated both potential and fragility. Fabi and Berger had the two quickest cars but a probable 1–2 finish was lost when Fabi over-revved his engine by lifting the rear wheels on a kerb, and Berger suffered a battery failure that cost him five laps in the pits.
The season's high point was the 1986 Mexican Grand Prix, the penultimate round. Berger managed his Pirelli tyres so effectively that he required no pit stop for fresh rubber, while principal rivals Alain Prost (McLaren-TAG), Piquet and Nigel Mansell (both Williams-Honda) each lost time to tyre stops or other mechanical issues. The Mexican victory was also the final Grand Prix win for the BMW M12/13 engine. Benetton outperformed fellow BMW customers Brabham and Arrows throughout the season.
The B186 was replaced for 1987 by the B187, which used a Ford turbo engine.
Of the seven chassis built, the known locations are:
Chassis 2: on display at the Mondello Park circuit museum in Ireland.
Chassis 4: written off by Fabi during practice for the Canadian Grand Prix.
Chassis 5: rebuilt and competing in historic racing in Sydney, Australia; later sold to a collector in Adelaide.
Chassis 6: on display at the BMW Museum in Munich.
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.
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