Yamaha's Masao Furusawa joined the company's motorcycle racing department at the same time as Rossi, and is considered as much a part of the M1's success as Valentino Rossi has been.
This graph shows how lateral, vertical and torsional chassis rigidity have changed over the years. Note especially the significant changes with the reduction in engine size to 800cc and the emphasis on corner speed.
At the end of each MotoGP season, Yamaha has released a technical document detailing that year's M1 and its continued development. 2010, however, was the end of an era as Valentino Rossi has now left the company and Masao Furusawa, long considered the architect of the M1, is set to retire. To mark the occasion, Furusawa presented a historical presentation at the end of the year outlining key engine and chassis features of the seven M1 models Rossi had ridden.
The Rossi years - 2004 through 2010 - cover both 800cc and 1000cc versions of the M1, although each was an inline four-cylinder engine with a crossplane crankshaft and 16-valve cylinder head. As discussed in the historical document, the common theme of development over the seven-year stretch was not maximum power or ultimate handling, but rather to maximize the connection between rider and machine as well as to achieve a balanced package that excels in all conditions - including hot and cold, wet and dry, and at the beginning and end of a race. And as the rules changed over the years - encompassing the switch to 800cc, reduced fuel capacity, spec tires in limited quantities and maximum number of engines - development focused on maximizing the bike's performance within those rules. How was this accomplished over the seven years?
This timeline of the M1 shows how little the overall silhouette of the bike has changed over the past seven years. Two areas of interest: The fuel tank has gradually progressed downward and rearward, while the side vents in the fairing have changed significantly to improve cooling. The company is careful to improve aerodynamics without sacrificing yaw performance - how quickly the bike turns about a vertical axis.
The first season for Valentino Rossi on the M1, elaborate off-season testing resulted in the use of the crossplane crankshaft - as used in the latest generation R1 - to improve rear tire traction and the connection between the rider's throttle input and power delivery, without sacrificing agility and overall handling. The chassis featured a short wheelbase/long swingarm combination with a lowered center of gravity compared with previous years.
An all-new chassis and physically smaller engine were intended to achieve the optimum balance between handling and engine performance in all conditions. The fuel tank was changed to further lower the center of gravity and reduce yaw, roll and pitch movements (roll refers to the motorcycle leaning side-to-side, pitch refers to fore-and-aft movement on the suspension, and yaw refers to the motorcycle rotating around a vertical axis). The engine's bore and stroke dimensions were changed and gear-drive cams were utilized, with more top-end power at the expense of midrange.
Frame rigidity along the three axes can be independently tuned partly by varying the height, width and material thickness of the main spars. The size and shape of the front engine mounts determine how much the engine contributes to chassis stiffness also; this especially has changed since '04. The crankcases are machined rather than cast, allowing changes in design to be more easily tested and implemented.
While the goals for '06 remained the same as the previous year, both the engine and chassis were completely changed again with a new bore and stroke for the engine and a new suspension link for the chassis, with the frame's rear crossmember removed and the shock mounted directly to the engine. Ride-by-wire throttle was introduced, with more rider-friendly torque delivery and electronic control of engine braking, traction, wheelies and launches. Peak power increased by five horsepower, while maximum revs increased by 400 rpm and fuel consumption remained the same.
The first year of 800cc displacement, tire restrictions and reduced fuel load, Yamaha's development concept focused on more cornering speed and better aerodynamics. Chassis stiffness was changed, while the new, smaller-capacity engine was approximately 7.5-pounds lighter and revved 2000 rpm higher. More elaborate electronics based throttle control on "real-time vehicle dynamics", incorporating bank angle, lateral acceleration, tire frictional force and a calculated optimal torque to regulate engine torque for traction and wheelie control.
A difficult year for the Yamaha team in 2007 resulted in part from a lack of performance, reliability, acceleration and top speed from the M1. Other problems included hard-to-manage fuel consumption, difficulty matching tires to the chassis, and compromises in balancing front/rear grip and braking/turning performance. These issues were addressed with significant chassis alterations, including changes in rigidity, geometry, wheelbase, center-of-gravity height and weight distribution (and, in part, by the switch to Bridgestone tires). The engine was made more powerful through the introduction of pneumatic valves (which reduced weight by 40 percent in the valvetrain) and reducing internal friction. Horsepower increased by 12 percent, while fuel consumption improved by six percent.
While the '08 M1 was an improvement over the previous year, those improvements came at the expense of stability and reliability - this especially was worrisome as new rules for '09 further limited the number of tires used at each event as well as the number of engines used over the course of the season. Updates to address these issues included a change in chassis rigidity, improved aerodynamics, further reduced internal friction and alterations to the airbox and fuel system. Chassis changes included a longer wheelbase and a lower and more forward riding position. Crankshaft inertia was increased by 10 percent to improve part-throttle performance. Elaborate use of CAE (Computer-Aided Engineering) was used to improve durability, with the example of reduced piston temperature shown. The wheelie control system was changed to incorporate pitch rate as opposed to fork travel to reduce power before the front wheel leaves the ground as opposed to after.
During the final year of the Rossi/M1 combination, development centered on further improving rider feedback and the "man/machine collaboration." Chassis balance and rigidity was again changed, and aerodynamics were changed to improve engine cooling. Gyro sensors were incorporated into the electronics package for wheelie and traction control, and engine durability was improved with the goal of 2000km (about 1250 miles) longevity.