BAR Honda, which had achieved 11 podium finishes and finished second in the constructors’ championship in 2004, retained its two race drivers, Jenson Button and Takuma Sato, but there were some changes to the team’s structure. David Richards, who had been team principal since 2002, retired at the end of 2004, and Nick Fry had been managing director of Prodrive under Richards, while also serving as managing director of BAR since 2002. As Richards retired from managing Prodrive, Fry had also left at the end of 2004 to become CEO of BAR Honda from 2005.

Although Prodrive withdrew from the management of BAR, a new joint venture company, BARH Limited was established with British American Tobacco (BAT), in which Honda held a 45 percent stake, creating a long-term, stable structure for competing in F1. BARH Limited did not have a president. Instead, Shoichi Tanaka, president of Honda Racing Development (HRD), Takeo Kiuchi, project leader, and Hiroshi Oshima, Honda’s executive officer in charge of public relations and motorsports, became derectors, and participated in BARH Limited’s board meetings as BAR Holdings’ board members.

The 2004 one-engine-per-race regulations were changed to one-engine-per-two-races this year, requiring even greater durability and reliability. Each engine needed to last an estimated 1,400 km. To meet this requirement, Honda classified corner load characteristics into five levels and conducted reliability tests by combining each load characteristic. The accuracy of the preliminary simulation was improved to ensure endurance reliability. This circuit simulation technology also optimized engine usage, such as maximum output rpm, up-shift rpm, and straight-end rpm required for each circuit, and provided power output characteristics knowhow to improve lap times. Honda, which had been a regular podium finisher with the 2004 RA004E, looked to develop a winning engine for 2005, and the result was a major shift from a design that pursued power to prioritizing lap times. In the 2000s, F1 circuits had fewer long straights and more turns of various shapes. In order to cope with this trend, Honda concluded that to improve lap times, it would be better to add more torque at low and mid-range speeds and improve performance at turn entries and exits, in addition to pursuing top-end power.

The engine’s framework was modified in consideration of the car’s kinematic performance. The weight of the RA005E was further reduced to less than 90kg, to an astounding 88.6kg. Furthermore, by lowering the cylinder heads, a more compact and lower center of gravity compared to the RA004E was achieved. The center of gravity height of 163.5mm was Honda’s lowest throughout its third F1 era. The BAR gearbox also featured a lightweight second-generation carbon composite casing, which was 10 percent lighter while increasing rigidity.

BAR Honda, however, had two problems that year that prevented it from reaching its full potential. The first was the controversial transfer of Jenson Button to Williams at the end of 2004, and the disqualification of Jenson Button’s car from Round 4, San Marino for violating weight regulations and subsequent suspension from the Spanish and Monaco GPs. These incidents early in the season under new aerodynamic regulations, when BAR Honda was on the rise, completely stalled the team. Button only managed two podium finishes that year, and BAR Honda dropped to sixth place in the constructors’ standings. Takuma Sato had difficulty to even finish in the points, scoring just one point all season.