Cycle News - Archive Issues - 2000's

Title-Winning Tricks Yamaha's first YZF-M I MotoG P racer back in 2002 measured 920c(, because its engineers' original concept for the bike was to make it narrow and small, with a good power-to-weight ratio achieved through a compact, inline four-cylinde r motor has been cured via suspension settings. But in spite of the supposed benefits of the new motor, the Yamaha remains harder on its rear tire than its Honda rivals, and it usually can't run as soft and thus as grippy a choice for race distance as Hondas can. The prototype of the current chassis first appeared at Valencia a year ago, with new upper engine mounts on the base of the cylinder block, rather than the cylinder head . It also featured a reversed, fully m achined swingarm , with bracing underneath rather than above to lowe r the cg. But th e bike was nevertheless raised 25mm overall for Rossi by the time he raced it lor the first time . It had also been using technology they were familiar With. This resulted in a lightweight chassis, with cylinders inclined forward by 15 degrees for better installation and weight balance. But after the success of Honda's RC211V disproved Yamaha's original content ion that the riding Rossi's Yamaha to the Rossi Honda RC21 1V I sampled a ye ar ago because it fe els smaller, has easi e r steering a nd has an even bette r engin e chara cter - leastways, for a rid er of my hum ble talents. It fe els hoo ked up , yet it is fast und er acceleratio n, stable under bra king and , ab ove all, so controll abl e and user fri endly. Eve rything abo ut th e bike feel s so refined , so balanced, and just so , well - right . In fact , it's my ne w best-eve r, succeeding the RC21 IV Honda that I rode a year ago as the best mo torcycle of any kind I've ev er ridde n in a qu arter-century ca reer of testin g the be st of the best. Hang o n, though: It's th e sa me rider who developed both bikes , wit h the same pit crew. Maybe that tells you so me thing - right , Honda?! eN gradually refined during the remainder of the season to en hance grip and traction, while still permitting high comer speeds and a tight turn angle. The six-speed gearbox is natu rally an ext ractable cassette-type transmission mated to a dry, ramp-style slipper clutch , w hose con vent io nal antilock funct ion under reverse torque loads during engine output of a full-capacity MotoGP engine would be unusable, the engine was brought up to a full 990cc in th e middle of 2002, by increasing both bo re and stroke from before. And for 2003 , the carburetors originally fitted were jettisoned in favor of fuel injection, primarily for superior fuel efficiency since consumption was becoming more of an issue - and will be even more so next season, w hen the current 24- liter maximum fuel capacity drops to 22 liters. Orig inally flat-slide throttle bodies we re employed, with Yama, ha's own engine management ECU. but with the two injecto rs per cylinder coming from Marelli, as well as some other parts. From Le Mans this year onward, a full Magneti Marelli EFI system with a sma lle r, lighter Formula I-derived ECU was fitted to Rossi's YZF-MI for the first time. This system was first developed on Norick Abe 's and Marco Melandr i's Tech-3 bikes. In its 2004 16-valve format, with firing pulses on two cylinde rs closed up to around 60 degrees of cran kshaft ro tatio n. followed by a space of around 300 degrees before the next pair fire close together, in order to improve traction and (theoretically) tire life, the YZFRI motor is even more unusual than it alreadywas. It runs backward as before, but the intermediate shaft (located between the crankshaft and clutch to reverse the direction of rotation) is now conve- niently able to be fitted with balance weights in order to act as a counterbalancer, thus eliminating undue vibration resulting from the "C'mon Vo le, take a closer look. You still swear you don't recognize me?I" uneven firing order. The one-piece crankshaft is still machined from solid billet and drives a short chain directly to an intermediate gear, which then actuates the double overhead camshafts. The titanium valves each have two springs and employ bucket-and -shim adjustment, while as before, the ultra-slipper two-ring pistons are mounted on titanium conrods . The Termignoni four-to-two -to -one titani- um exhaust is one of the few on the MotoGP grid to still be fitted with a silencer, a we ight penalty wh ich Yamaha can afford since , as before, the YZF-MI scales in right on the MotoGP weight limit, especially after this was raised to 148 kg (325.5 pounds) for 2004 . The YZF-MI is still a short-stroke design, though not extremely so - only a little more heavily oversquare than Yamaha's R7 Superbike, for example . In 2003, engine output was 240 bhp at 15,350 rpm measured at the crankshaft, 25 bhp more than the previous year's smaller, carbureted engine, to which Yamaha claims to have added an extra 10 bhp this past season to flirt with the 250 bhp barrier. Yet the YZF-MI is still down on outright power compared to the Ducati and Honda, though this is offset by its lighter weight of I 10 pounds, some 30-percent lighter than the RI 5uperbike engine of the same capacity (and over 17 pounds less than an R6 Supersport 600 motorl), And at 350mm wide, the M I is 20mm narrower than the RI (and 40mm slimmer than the R6), as well as more com pact: It's l-pe rce nt shorter in length and 5-percent lower in he ight than the RI. This originally allowed Yamaha to design a smaller, lighter De ltabox chassis, and while for 2003 this had II-percent more torsional rigidity than the first year's frame, and 14-percent greater pitching stiffness, the latte r was considerably decreased for 2004 to redress Rossi's complaint tha t the bike was too stiff. The YZF-MI also suffered badly fro m rear wheel chatter in 2003, a problem that le ngthe ned by 20mm . Continued experimentation at each race - and especially for the wet, w here handling continued to be a proble m - led to a new chassis appearing at Assen . The new version w as braking . This is further supplemented by an electric motor. The motor operates a so-called "kicke r" system, introduced for 2003 and proper ly kno wn as an id le co ntrol system (IC5). This is a quite simple electronic solution whereby the throttle co ntro ls the opening of th e four throttle bodies, but two of these, how ever, are influenced by the ICS. Even afte r the rider has shut the throttle unde r braking, this adjusts the opening based on th e input of th e ECU during deceleration, w hich monitors front and rear wheel speed , throttle opening. engine rpm, gear selected and braking pressure to raise the idle spe ed as appropriate to prevent the rear wheel chattering. For 2004 , what was previously a setup using preset engine map ping became a real -time system, which factor ed tire , weather and track cond itions into the ICS kicker response. But the rider must still use the clutch to backshift, because operating this trigge rs the system , wh ich has also been considerably down played electron ically from last year's, to give more feel. And further electronic control is supplied via traction control, which Yamaha employs off the start line and then again in the race if the tire is losing grip, at wh ich po int the r ider can select a different map with less aggressive characteris- tics via the switch on the left handlebar. Yamaha 's pres surized carbon airbox on the YZF-M I is now over 20-percent large r than when it began MotoGp, and it is fed by the biggest intake duct on the MotoGP grid, positio ned beneath the nose of the fairing to deliver high-pressure ram air w it ho ut sacrific- ing the engine's cooling efficiency. It's so big, the bottom lip of the carbon-fiber intake mouth has to be flexible so as to give way when the front mudguard touches it under heavy braking! For optimum cooling , Yamaha uses big MB Motorsports radiators manufactured in Italy,which are very light and well made . This increased airbox capacity is a direct result of the low-slung fuel tank, wh ich carries mo st of its 24-liter capacity low in the chassis to pro vide space for the larger airbox. But this also has extra benefits , as it lowers the center of gravity and reduces the pitching effect experienced under heavy braking with a full fuel load. Yamaha's aim in developing the YZF-M I with its transverse inline motor was to concentrate mass and reduce polar moment as much as possible . The goal was to achieve better balance in handling aimed at maximizing corner speed. to deliver more neutral handling and to improve traction so as to give the rider confidence to accel- erate ea rlier and brake deeper into the turns. This setup allowed the team to use the bigger footprint of Michelin's new 16.5-inch front tire, introduced this season, to optimum effect . The result is a weight distribution that is now is 56/44-percent static , but more importantly an even 50/5 0 split with a rider of Rossi's we ight in the hot seat - the optimum target to achieve the above objectives . Ohlins' new TT25 dual-cartidge 42mm inverted fork was used all season, while Brembo rad ial calipers grip e ither 305mm or 320mm carbon discs, depending on the circuit - and it's worth noting that Rossi sometimes runs shrouds on these to keep up disc temperature, perhaps an issue because he doesn't brake as hard as his Hondamounted rivals, using more turn speed to help redress the top speed and outright power handicap the Yamaha suffers at present. Rossi's Yamaha was 12th fastest through the speed traps down the Catalunya circuit's long front straight. yet he still had the quickest lap time . Hmmm... C YC LE N EWS • JANUARY 5, 2005 37

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