Once the supply of spare parts had been assured by mid-season, the B186s were modified to incorporate a whole array of new aerodynamic features (including front and rear wings and a revised underbody), new suspension packages, and revised setup concepts. The chassis was also strengthened further to cope with the stress caused by the power of the BMW engine. The development package was completed by the arrival of a new rear wing design for the Austrian Grand Prix, where the improved performance of the B186 and the high-speed Österreichring circuit made it the fastest car in the field with Fabi (pole) and Berger occupying the front row of the grid. The car's competitiveness improved throughout the season, particularly during the second half, as a result of this development. It also became more reliable, although this aspect remained suspect throughout the year with a total of nineteen retirements from 32 starts. The competitiveness of the Pirelli tyres also improved, and their relative durability compared to the Goodyears often played to the B186's advantage, exemplified by Berger's winning the 1986 Mexican Grand Prix due to not having to make a pit stop for a fresh set of tyres while most of the main contenders (with the exception of Prost's McLaren which finished second) made at least two stops for tyres due to the abrasive surface of the Autódromo Hermanos Rodríguez.