The adoption of the new 800cc MotoGP regulation this year marks the end of a 5-year era of the 990cc 4-stroke machines that began in 2002 with the shift from the GP500 to the MotoGP.Here is a history of the evolution of the 990cc M1 that competed in the MotoGP in its first five seasons.
Engines
 The YZR-M1 born in 2002 was based on a 4-stroke engine and the chassis that had been used for the 500cc YZR500. An in-line-4 engine was adopted on that first M1 as an optimum layout to achieve the development goals dictated by the YZR-M1’s design concept, which called for a longer swing arm and a shorter wheelbase. The longer rear arm was made possible by the gradual shortening of the crankshaft and axle drive for this engine year by year.There were two main changes in the 2003 model. Fuel injection was adopted instead of a carburetor and an ICS system was also adopted to replace of engine-brake control system. Furthermore, in 2004, the performance of the YZR-M1 was dramatically improved with an introduction of an uneven firing interval and a 4-valve cylinder head.
In a test for the media conducted in the off-season in 2003, the engine was evaluated as being very aggressive and difficult to control. Everyone who saw the test results were saying that 2004 would be a very tough season for Valentino Rossi. But, at the time, development of a 4-valve, uneven firing interval engine had begun, and tests on this new engine started around the Christmas.When Rossi rode the M1 with the new engine, he decided that the development concept for the engine was going in a good direction. From then on, year by year, max. output and rpm would be improved. The engine was given a short stroke in order to increase rpm. And, to accommodate this, the valve train system was changed from a chain to a gear type.
EMS Engine Management System
 An engine and its EMS (engine management system) can never be taken separately. At the time of the M1 development in 2002, EMS meant little more than control of the engine brake effect. All the teams had to deal with the problem of controlling the engine brake effect of a 4-stroke engine. This was also a problem with the YZR-M1 and numerous systems had to be tested. It can even be said that the problem of engine brake control was the driving force behind the development of EMS. The max. output of an engine is naturally important but good controllability is also a necessity.Through development, a fly-by-wire system came to replace the ICS system. Thanks to this change, the throttle work can control not only the engine output but also the chassis.
Chassis
 The frame of the YZR-M1 is designed with a greater torsional “forgiveness” and less rigidity in the lateral direction, while maintaining rigidity in the vertical direction. When a motorcycle is banked, the frame itself has to function like a suspension, because the suspension of a motorcycle basically functions only in the vertical direction. For this reason, many methods were used and many tests made in this area of frame development. In 2005 a cross member was removed. This reduced torsional rigidity and rigidity in the vertical direction, which greatly improved machine agility and stability. At the same time, the air intake passage was designed to run through the head pipe, which contributed to increased engine performance.The concentration of mass toward the machine’s center of gravity is very important for improving a bike’s handling. Recent years, development efforts have focused on the fuel tank and electronic control parts and the engine as components that can improve the concentration of mass.
 It is easy to imagine that the shape of a fuel tank contributes to mass concentration. At the same time, the mass concentration contributes to minimize the difference in the weigh balance when the tank is full and empty. The main electronic control parts used to be positioned underneath the front panel. The ECU, measurement parts and other related parts are not very heavy and therefore have little effect on mass concentration, but it was considered a potential problem that they were positioned so far from the center of gravity of the machine.To solve the problem, the electronic control parts were moved to the tank rail, which made for a dramatic improvement in mass concentration. As for the engine, efforts are constantly being made to make the design as compact as possible and to find the optimum mounting position for the engine.These improvements in mass concentration have effectively reduced the inertial moment of the machine and have thereby reduced the movement with regard to each axis year by year. And this results in positive improvements in cornering speed.
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