[2] Yamaha wanted to preserve the superior handling of the YZR500, so the M1's engine was designed to fit in a chassis developed around the basic structure of the YZR500.

[2] The frame design also evolved during the season, with adjustment of the engine mounting position and change in the fuel tank shape.

[4] M1 riders were Checa, Alex Barros, Olivier Jacque, Marco Melandri, Shinya Nakano and Norifumi Abe, and there were no wins and Yamaha came in third in the manufacturers' championship.

Valentino Rossi signed a two-year contract with Yamaha, reportedly worth in excess of US$6 million per season, in a move that was described by the press as "biting off more than he could chew".

It was widely felt not only by his critics and media pundits but also by many fans, that even he would not be able to bring the struggling YZR-M1 up to the level of the hitherto all-conquering Honda RC211V.

This was a shrewd move and was cited by Rossi in his autobiography as instrumental in providing him with the strong basis necessary for launching an attack on the Championship with the YZR-M1.

Yamaha engineers under YZR-M1 project leader Koichi Tsuji experimented with a number of engine modifications in an attempt to fix the power delivery, and finally it was decided to go ahead with a four valve per cylinder head configuration (as opposed to the earlier five-valve head), with a specially refined cylinder firing order.

The YZR-M1 and Rossi partnership continued to dominate in 2005 when the Championship was won by a massive 147 point margin over Honda rider Marco Melandri in second place.

This setback for Yamaha and the YZR-M1 was largely responsible for Valentino Rossi's mediocre start to the 2006 season, manifest by poor qualifying performances and a brace of bad luck.

In the final third of a memorable season, the M1's problems were virtually eradicated, and Valentino Rossi turned in a string of performances that almost closed a large points gap on Championship leader Nicky Hayden aboard the Honda RC211V.

[5] The main sponsor for the Official Factory Yamaha Team switched from Camel, with their distinctive yellow and blue livery, to that of the Italian motor manufacturer Fiat.