In mounting one of the most impressive comebacks in Grand Prix history (even if it did come up a little short), Valentino Rossi demonstrated that the '06 version of Yamaha's inline-four YZR-M1 still had the necessary performance to win in MotoGP. Winning five races over the course of the season (more than any other rider), plus teammate Colin Edwards II coming within 300 feet of winning the Dutch GP, was ample proof of the bike's potential. Only some bad luck and a certain rider by the name of Nicky Hayden prevented Rossi and Yamaha from notching up their third consecutive MotoGP crown.
After five years of a 990cc displacement limit for the MotoGP category, 2007 sees the MotoGP machines shrink to 800cc. Although many are predicting that the overall power and speeds won't decrease that much in the switch to the smaller displacement, the fact that '06 was the curtain call for development of the liter-class machines made the opportunity to try out the last of these racebikes before they disappear something that couldn't be missed. Thankfully, yours truly got the call to fly out to Valencia's Ricardo Tormo circuit for a 15-minute test session on Rossi's M1 racebike. It was truly an eye-opening experience-and no, not because of the sheer speed and claimed 250 horsepower.
Development Of The Yzr-M1
Since this was the last of the 990cc-generation machines, Yamaha was much more open about many mechanical aspects of the M1 without fear of industrial espionage. This included many details regarding the M1's development process, from its debut years in '02 and '03 with riders Max Biaggi and Carlos Checa to the then-present form at Valencia with Rossi and Edwards.
Although the inline-four engine architecture was used throughout the M1's lifespan (and continues onward to the 800cc era), continuous evolution enforced by the intensely competitive arena of MotoGP resulted in numerous changes to both engine and chassis in an effort to maximize handling agility, power and the ability to fully use that power. As power outputs inexorably rose higher with every year (from its '02 debut to the final version of the '06 M1, power increased a total of approximately 35 horsepower, with a corresponding 3000-rpm increase in rev limit), tire technology increased as well, leading to ever-higher levels of grip. However, that increased level of traction led to chatter from the increased loads, requiring constant changes to the chassis. It's also interesting to note that the engine's overall size shrank every year despite the ever-increasing power output, enabling Yamaha engineers to lengthen the swingarm for improved handling and traction feedback.
The original '02 M1 used the chassis from the previous YZR500 two-stroke in order to gauge which direction to take with that area of development. The engine used a conventional even firing pattern that unfortunately made the bike difficult to handle accelerating off corners due to the engine's 210-horsepower output. Biaggi managed to score two wins that year and finish second in the points standings, but Rossi, then on the RC211V, had easily sewn up the title with several races to spare.
'02 Version of the YZR-M1 | 
'03 Version |
'04 Version | 
'05 Version |
'06 Version | |
In '03, Yamaha tried to soften up the M1's power by using electronic fuel injection for the first time (the previous version actually used flat-slide carburetors), as well as adding the ICS (idle control system) to reduce the engine braking effect into the corners. However, power was also increased by about 10 horsepower via a more oversquare engine configuration, and all four of Yamaha's riders that year complained of the engine still being difficult to handle, as well as the ICS being inconsistent in performance.
Big changes ensued for '04, with Rossi's sensational defection from Honda to Yamaha overshadowing the major revisions to the M1's engine. The signature Yamaha five-valve cylinder head was dropped in favor of a four-valve unit, the bore/stroke ratio was once again made even more oversquare, and the crankshaft firing order was changed to an uneven pattern that was easier on both rider and rear tire. The chassis also underwent some subtle modifications that reduced lateral and torsional rigidity with the goal of quelling the midcorner chatter problems that were encountered with the new breed of ultra-grippy racing slicks in MotoGP. But it was the Long Bang firing format that was credited with improving traction and tire life enough to enable Rossi to garner yet another world title.
The following season brought with it a new 22-liter fuel-capacity regulation (down from 24 liters) that required improved fuel economy, in addition to a necessary increase in power to address the specter of Honda looking for some payback for losing the '04 title. Increasing power meant-once again-shortening the stroke for more rpm (resulting in a gain of more than 1000 rpm on top). In order to keep the engine's overall dimensions as compact as possible, the hybrid chain/gear cam drive was converted to a complete gear-drive assembly and moved to the center area behind the cylinders. The chassis also underwent further revisions aimed at reducing lateral and torsional rigidity even more in the pursuit of improved cornering feel. Engine electronics also reached new heights in power and capability, with traction control now enabling even better late-race tire management.
Valentino Rossi's 990CC Yamaha YZR-M1
Changes For '06
Design revamps for '06 were aimed at even better agility and improved braking stability-along with the usual helping of more power while still keeping fuel consumption in check. In order to obtain that additional power, the M1's powerplant was amazingly made even more oversquare, with a shorter stroke/bigger bore allowing an extra 400 rpm and five horsepower on top. Chassis changes were initially limited to a slight stiffening of the rear shock mounts (the upper rear frame cross-member was removed in '05 for less rigidity and better midcorner feel, with the top shock mount now in the engine cases), but problems with chatter in the beginning of the '06 season forced some modifications to the original frame twice during the year.
Instead of the previous "2 x 2" fuel injection system (two throttle plates were controlled by the rider, while the other two were controlled by the engine-management system), improvements to sensors and power of the Magneti Marelli EMS allowed Yamaha engineers to build a total fly-by-wire throttle-control system-with all throttle plates under EMS control-that also enabled them to develop and incorporate wheelie and an improved start launch control. Braking stability was enhanced by the development of a sophisticated slipper-clutch system that utilizes a combination of air bypass, clutch slip and idle speed all controlled by a fuzzy-logic microprocessor that permits actual adaptation to racing conditions, a far cry from the previous system that only controlled idle speed.
Rossi's Ride
As I hop aboard after the mechanics fire up the M1 using the rear-wheel trolley starter, it's hard to ignore the high, 3000-rpm idle speed common to all MotoGP bikes. A quick examination of the dashboard reveals the usual Marelli LCD display now common to most MotoGP racebikes, including the bar-graph tachometer that is basically impossible to read at speed (which is why the shift lights atop the dashboard are so necessary). Snicking the M1 into first gear and starting off down pit lane reveals a tall first gear and a clutch that doesn't have a whole lot of feel; again, not an issue, since the riders use the launch control for race starts.
The carbon-fiber airbox bristles with the electronic boxes for various data-acquisition functions.
The first surprising aspect of Rossi's Yamaha is just how hyper-responsive the engine is. This is not to say the response off closed throttle is abrupt; in fact, in that respect, it's one of the smoothest racing engines I've tried. It's more the response once you twist the throttle past 40-percent open anywhere above 8000 rpm. Once the throttle is opened past that point, the torque curve jumps up substantially, with acceleration becoming much more aggressive. So aggressive, in fact, that initially I was preparing for the front wheel to shoot skyward out of many corners, but thankfully, the wheelie control helps keep chassis attitude well under control, allowing the M1 to stay hunkered down and accelerating hard. Interestingly, however, the wheelie control fails to keep the front end from coming up over the rise on the front straight while pinned in third gear, forcing me to short-shift into fourth (stomping on the rear brake seemed to scrub off more speed than short-shifting). Top-end power is, as expected, eyeball-flattening, although I can feel the acceleration tapering off a little just before the red shift lights atop the dash signals that the 16,500-rpm rev limiter is approaching.
Steering effort is a little higher than I expected, especially during major directional changes; a fair bit of muscle is required when flicking the M1 from one side to the other at full lean. Still, front-end feedback is superb during cornering situations, with sharp, precise steering that makes me feel as if I could put the bike anywhere in a turn, especially while trail-braking on the entrance.
The other surprising feature of Rossi's M1 was the carbon brakes-specifically, the fact that they were high-effort and required a lot of lever travel before serious braking power came online. At first, I thought perhaps the Yamaha's brakes just needed more heat in them, but the same high effort was required at the end of the session as it was at the beginning. Granted, the power and feel were there once I applied them hard enough; it's just that it required a lot more effort than usual. After thinking about it, I realized that's the way Rossi likes his brakes; if you see any onboard camera footage of Rossi's throttle hand during the race, you'll notice that he uses all four fingers for braking.
The '06 version uses crankcases CNC-machined from solid aluminum billet; a deep sump keeps oil away from the crankshaft. | 
The radiators and the titanium exhaust are works of art |
The front engine mount allows just enough flex in the chassis to improve cornering feel & reduce the resonations. | |
The Yamaha's sophisticated slipper-clutch system worked extremely well, preventing the rear tire from causing any problems, no matter how hard I used the brakes. It didn't matter whether I grabbed a handful of gears and let out the clutch, or did them in rapid-fire succession, or tried to blip the throttle between downshifts; the system would simply feed in just enough air bypass (to ease compression), clutch slip and engine rpm to provide a smooth, effortless downshift.
A Storied Pedigree
While most will give all the credit for Yamaha's two consecutive MotoGP world championships to Rossi, it shouldn't be overlooked that Yamaha also made some strategic changes to the YZR-M1 when he arrived that proved to be instrumental in giving Rossi the performance to attain his '04 and '05 titles. It's pretty apparent by the constant changes to the M1 every year since its inception that Yamaha was very serious about taking the MotoGP crown and devoting the necessary resources to do it. An extraordinary amount of technical knowledge and innovation went into the M1, and now that the MotoGP class has downsized to 800cc, much of that knowledge will be transferred to the new M1, which retains the inline-four engine architecture.
And you can bet that Yamaha will be putting every ounce of that technical expertise to use in regaining the MotoGP crown in '07.