The McLaren MP4-20 incorporated all of the lessons that had been learned, from the MP4-18 and from the two iterations of the MP4-19. The MP4-20 looked quite different from its immediate predecessor, partly thanks to a change which was brought about by the new set of rules drawn up by the FIA for 2005. The front wing had to be raised another 50mm, the maximum height of the diffuser was restricted, and the rear wing had to be moved significantly forward, all in an attempt to reduce downforce.
Changes were accordingly made in these areas, together with detail revisions to the deflectors and barge boards around and behind the front suspension. Technical Director Adrian Newey believed that downforce had been cut by as much as 28 per cent, according to wind tunnel data. The suspension geometry was also revised, a large amount of work was carried out on the critical hydraulic systems, and there was a new version of the Mercedes-Benz V10, the FO 110R, which was required now to last for two GPs.
The early races were tough. Heavy rain during qualifying for the Australian opener left Räikkönen 10th and Montoya ninth on the grid and they worked up the field to finish eighth and sixth respectively. Montoya was fourth in Malaysia, but Räikkönen lost a possible victory. He was leading and had set fastest lap by the 24th tour, but a rear tyre deflation, due to a valve failure, forced him into a spin and then to crawl round for a replacement. He recovered to finish ninth.
Montoya injured himself prior to Bahrain and had to be replaced by Pedro de la Rosa - who finished fifth as Räikkönen made the podium with third place. Alex Wurz, standing in for Montoya, repeated that result in San Marino, where a driveshaft failure halted Räikkönen.
The big breakthrough came in Spain, where a dominant Räikkönen beat season pacesetter Fernando Alonso’s Renault fair and square as a recovered Montoya bravely took seventh after a spin and problems with his refuelling rig. McLaren was back on track, as Räikkönen proved with another decisive win in Monte Carlo, where Montoya followed Alonso home with fifth place. The battle for the title was distilling into Alonso versus Räikkönen, with 49 and 27 points apiece.
A hat-trick was denied Kimi at Nurburgring when a calculated gamble to get to finish with a flat-spotted and badly vibrating tyre backﬁred on the last lap, breaking the McLaren's right front suspension and forcing a non-finish as a grateful Alonso inherited victory. Montoya was seventh.
Räikkönen bounced back to win in Canada, then came the controversial US GP at Indianapolis where all the Michelin runners were forced to withdraw after the warm-up lap because of tyre problems. That was particularly galling for Kimi as he had qualified on the front row, and because a flypast win for Michael Schumacher brought him within three points of the Finn’s 37.
Alonso still led with 59. They finished in the order Alonso, Räikkönen, Schumacher in France, then Montoya won his first race for the team at Silverstone as Räikkonen completed the podium behind Alonso. Now the Spaniard had 77 points, the Finn 51. Alonso beat Montoya in Germany, with Räikkönen retiring after 35 laps with a hydraulic leak after leading from pole. With a 36-point advantage, Alonso looked safe until Kimi sliced away 10 by winning in Hungary, and another two by beating Alonso in the first Turkish GP. Now the gap was 24.
Montoya took a second victory to endorse the performance of the MP4-20 in Monza, where Alonso finished second and Räikkönen fourth after an engine failure in practice negated his pole position and obliged him to fight through from 11th place on the grid. At Spa he got his revenge, leading Alonso home as Montoya controversially crashed while lapping Antonio Pizzonia’s Williams. Montoya then led a McLaren 1-2 in Brazil. It was the team’s 40th. Third place there was sufficient for Alonso to put the title beyond Kimi’s reach, however, with 117 points to 94.
The Japanese and Chinese GPs remained. In the former Kimi drove the race of his life. Everything went wrong for the team in qualifying when both he and Montoya started from the back of the grid after sudden rain in qualifying rendered things a lottery, Kimi started 17th, Juan Pablo 18th. The consolation was that close rivals Michael Schumacher and Fernando Alonso were 14th and 16th. Montoya was eliminated in an accident on the first lap and Giancarlo Fisichella should have won for Renault, but Räikkönen drove a blistering race to catch and pass all of his rivals and deny the Italian literally at the beginning of the final lap.
Alonso bounced back to beat Räikkönen in China, with Montoya falling out after 24 laps. Thus a gripping season of redemption for McLaren ended with 10 victories, Räikkönen in second place in the Drivers’ World Championship with 112 points to Alonso’s 133 and Montoya fourth on 60 and McLaren-Mercedes second to Renault in the Constructors’ with 182 points to 191.