Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/128184
Suzuki GSV-R MotoGP Racer reverse loads are high, and re-engaging smoothly. This resolved the problem - but in the meantime Roberts was now permitted to downshift without using the clutch lever at all or blipping the throttle manually, by means of Toomey & Co.'s perceptive use of electronics, whereby the engine management system's ECU is automatically programmed to blip the throttle a little in response to slight pressure on the gear lever with the rider's foot, to help control the engine braking. This allowed Kenny (and Sete) to drop back two or more gears at a time, two-stroke style, without working the clutch and without locking the back wheel - though they also needed to remember not to bounce the valves at the same time. Can't completely ride it like a stroker - just mostly! "We realize this isn't the most efficient way to downshift," says Toomey, "but it works okay, especially with the new clutch, and Kenny's got used to it, though after his arm op he can now blip the throttle when he wants to - he's joined the four-stroke club! Just gives an extra option in the heat of action." This new engine is installed in a twin-spar aluminum chassis fabricated using special Suzuki extrusions which help deliver controlled flex, whose geometry is closely derived from the last RGV500 frame, says Tamomiya. It has the same external width, but it is modified for the increased demands of extra power and weight, and with a longer swingarm both to enhance traction and to help load up the front wheel weight-wise for added grip in turns. The result is a rangier 1420mm wheelbase for the GSV-R compared to the 1400mm of the RGV500, but the dry weight is very close to the 145kg (320 pounds) class limit for four- or five-cylinder round-piston machines - albeit inevitably 14kg (about 30 pounds) greater than the old 132kg (290 pounds) 500cc bike, say Suzuki. Roberts uses 320mm Brembo carbon brakes with radially-mounted four-pot calipers (Sete preferred smaller 305mm discs, which stayed hotter, longer), with Ohlins 42mm upside down forks and a rear shock matched to a Suzuki rising-rate progressive link. Worth noting also are the light but very sturdy Japanesemade forged-magnesium wheels which help reduce unsprung weight (a critical aspect of optimizing suspension response) without sacrificing robustness and the work of art which is the rear swingarm, consisting of various pressed-aluminum sections welded together to fabricate a unit with optimum rigidity - which is to say not too much, as well as not enough. Interesting, too, that at done pretty well for the first year of development, considering the bike only ran for the first time a year ago." After inevitable early teething problems were duly resolved - inciuding actually firing up the engine in the pit lane, where mechanics initially had to remove a couple of clutch springs to allow the hand-starter to turn ·over the high compression motor - the only recurring mechanical complaint centered around the six-speed transmission, where Roberts and Gibernau, two riders who'd each spent their entire career exclusively racing two-strokes, found it hard to adjust to the demands of back-shifting under heavy braking from high speeds with the four-stroke engine and blipping the throttle to match revs for each downshift while working the clutch lever in and out. Suzuki originally employed the same spragtype slipper clutch on the GSV-R as fitted to their GSX- R7 50 works Superbike, aimed at eliminating rear wheel hop under the reverse loads provided by engine braking. However, just as that bike requires a very high 4000 rpm idle speed to be employed so as to mask the inconsistent performance of the sprag clutch, which operates to preset values, so it proved less than ideal on the MotoGP bike - especially with its higher compression ratio and greater reverse loads of the bigger piston masses. "It's Kenny's desire to change gear with the clutch, as a matter of course" says Toomey, who, as a former winner of the NZ GP on a 1000cc Suzuki four-stroke, has some experience racing a four-stroke. "But because he was used to the 500, where you pull the clutch in just a small amount and hook back all the gears in succession, coping with the action of the sprag clutch was a real problem. He couldn't get the clutch to release enough to shift back through the gears. Plus the fact he had to blip the throttle-between each shift meant his arm was getting tired while also coping with the much fiercer braking from the carbon discs which Superbike riders don't get to use, with the extra weight transfer and increased instability that brings with it, especially if it also means you're chattering the rear tire into a turn because you can't get the slipper clutch to work properly. All this made us start thinking what we could do to help while Suzuki worked on a different design of clutch - and we decided to use the electronics to do this." After Kenny suffered so badly with arm pump that he needed to have an operation after Assen to cure it, Suzuki produced a very compact ramptype slipper clutch for Estoril in September similar to that employed by their rivals, which is self-compensating, slipping progressively only when 20 DECEMBER 1 1, 2002' cue • e n eVIlS Phillip Island the team cut large chunks out of the front of the fairing flanks to combat the sea breeze lifting the front end and costing grip - but without making any difference at all to top speed. At Mugello the Suzuki was clocked at 312 kph/194 mph 10 kph down on the 200-mph Hondas and Yamahas, a gap which increased to a massive 13 kph at Rio, for example, and meant the RGV-R was hardly any faster than a works Ducati Superbike. Suzuki has a praiseworthy track record of success in the black art of conjuring up a balanced, good-steering bike, and Tamomiya admits that his team experimented throughout the season with altering the engine position in the chassis, both up and down as well as fore and aft, in order to search for this, and they also produced ongoing versions of the frame throughout the season, with extra bracing around the steering head and various other key areas - all exactly what you'd expect from prototype R&D work. But remember, Suzuki did it all in public this past season, rather than behind closed doors. Good luck to Suzuki: you've only got to look at its Kawasaki rival's progress during 2002 to get a handle on this. The two Japanese firms each debuted their new bikes in the public gaze at Sepang The GSY·R's longer (than RGV) wheelbase and trick Ohllns suspension keep the bike planted In all conditions, although Cathcart slid the rear wheel, thanks to the generous bottom-end power mated to standard issue last January - but Suzuki chose to do its R&D in the public gaze by actually racing it throughout the 2002 season, rather than follow Kawasaki in spending a year in closed circuit R&D testing interspersed with a few Japanese national races and end-of-season wild card GP entries. The result? At the Malaysian GP on the same track at the other end of the season, the singleton Kawasaki fmished 19th - last, while Kenny Roberts took his Suzuki to rather more promising eighth place. "What we've learned this year in racing the bike even though it's brand new, we'd never have discovered in testing," says Bob Toomey. "It would have taken two years for us to find out what we now know, and to have got where we are today with this prototype bike - and to know what we need from next year's machine, which we aim to win races with. That's a realistic goal which we'd never have had a chance of targeting realistically if we hadn't done what we did this season. It was worth it." CN