The 2004 YZR-M1 will forever be remembered as the machine with which Valentino Rossi sensationally won Yamaha's first premier-class world championship since 1992 but, with the Italian's Honda contract preventing him from testing the machine until late January, much of the bike's design was decided upon without input from Rossi and crew chief Jerry Burgess.

Despite the delay Rossi, his race team and Yamaha soon began to manipulate the '04 machine - refining it ever further throughout the season - and it would go on to win no less than nine races. Nevertheless, it is the 2005 YZR-M1 that is arguably the first true Rossi/Burgess Yamaha, with the pair instrumental in steering its development from concept to world championship glory.

So how did Rossi, Burgess and Yamaha make the 2005 M1 - which won 11 races on the way to a perfect clean sweep of MotoGP rider, team and manufacturer world championships - even better than its predecessor?

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At September's Japanese Grand Prix, with Rossi on the brink of his seventh world title, Yamaha gave a technical presentation on its YZR-M1 project - which included a review of the 2004 machine, Yamaha's development targets for the 2005 racer and the performance results of that development programme.

This is what was revealed - diagrams and data provided by Yamaha, click on pictures to enlarge...

Review of the 2004 YZR-M1.

Yamaha's main target for the 2004 machine was to create a linear relationship between throttle opening and rear wheel traction (see diagram (1) in top picture), while exploiting the benefits of an inline four-cylinder engine layout (see diagram (1) in middle picture) to achieve a high level of agility, while maintaining stability.

As mentioned, the machine went on to win nine races and the riders' world championship in Rossi's hands, but there were also four races at which the YZR-M1 failed to reach the podium - at Jerez, Rio, Sachsenring and Losail.

In summary, Yamaha felt that the strengths of the 2004 machine were its quick handling ('agility with stability') and engine management systems, but that it suffered relative to the competition in terms of acceleration and top speed, plus a lack of wet weather stability.

Development targets for the 2005 YZR-M1.

With the above in mind, Yamaha set the following targets for the 2005 YZR-M1, a machine with which the company hoped to win all three MotoGP World Championships in Yamaha's 50th anniversary year:

1. To maximise the inline four-cylinder engine layout to further improve agility and stability.
2. To improve top end power and acceleration.
3. To increase engine efficiency in terms of fuel economy and engine output.
4. To improve performance in adverse weather conditions, such as wind and rain.

In order to achieve these goals, Yamaha designed a new engine and chassis for 2005.

One of the most important design features for the new machine, to help improve its dynamics (see diagram (3) in top picture for dynamics results), was better mass centralisation.

This was achieved by moving and reshaping the fuel tank, building a more compact engine (see diagram (4) in top picture) and placing the mounting point for the rear shock inside the frame - all while keeping the same wheelbase (see diagrams (2) and (3) in middle pic).

Meanwhile, frame rigidity was optimised by removing a chassis cross member (see diagram (2) in top picture).

Results of the 2005 development programme.

In terms of engine performance, the initial 2005 powerplant used at the Jerez season opener produced more top end power compared with the 2004 version, with further engine developments - introduced later in the season - increasing top end even further (see diagram (1) in lower picture).

But in some cases less outright engine performance was needed, which is where the 'torque control system' helped improve drivability. The system restricted top end torque in all but sixth gear, although it wasn't needed lower down in the engine powerband (see diagram (2) in lower picture).

In terms of top speed, the 2005 engine produced an average increase of just under 5 km/h from seven of the first nine races of this season, with the biggest top speed increase seen at Mugello (approx. 7.5 km/h). However, top speed fell by around 3km/h at both Assen and Brno (see diagram (3) in lower picture)

Results for fuel economy showed an average increase of 8%, with consumption well above 5 km/litre at all events listed (see diagram (4) in lower picture).

The 2006 YZR-M1.

So how will Yamaha make the 2006 M1 - the last incarnation of the YZR-M1 before MotoGP engine capacity is reduced from 990cc to 800cc - even better again?

A prototype version of the new M1 made its official track debut at Sepang last week, where - apart from the never ending search for greater engine performance and tyre grip - factory riders Rossi and Colin Edwards were impressed by its increased stability, suggesting that similar priorities to those which worked so well for 2005 are again being pursued...