Cycle News - Archive Issues - 1990's

-- '. (th ank s to th e usu al w ork on cylinder p o rtin g, h ead s, p ip es a nd ig n itio n cu rve) b ut that extra power is spread ove r a m uch wider ran ge than before. The Aprilia carburets as low as 9000 rpm, comes on strong at just over 10,000 revs -but smoothly, without th e kick in d elive ry th er e was last year wi th th e firs t low-lead mo tor - and builds hard and strong to its lOG-horsepower peak at 12,800 rpm and beyond. It' s a mark of how wide th e powerband is, and how flat the torque curve, tha t in '95 Aprilia actually ha d the luxury of being able to gear their 250 to use just a five-s peed gearbox at some circui ts, like Max did at Donington , for exa m ple. Th at ' s fourstroke territory! With the long fro n t s t raight a t Mu gello, yo u need all six ratios in th e ex trac ta ble gea rbox (w ith integra te d spee d shifter ), but it pays to make like Max and st re tch th e powerban d w hen shifting up , even if Biaggi doesn't overrev the bike as much as most other riders d o, says Jan Wit teveen. Still, the Aprilia, with its carbon-fiber rotary va lves, has a huge overrev capacity. When properly jetted it will run to 14,000 rpm without power falling off dramatically. Changing up at 13,200 rpm or so, as Biaggi does, allows you to pop the Aprilia's motor back into the fat part of the torque curve at around 12,000 rpm, thus ensuring maximum engine acceleration back to the peak power mark again. To re mind h im w hen the engine's ready to be thus pop ped, Max has a ju m bo -size version of an idea that he ad opted last season for the first time, which I noticed Honda has now copied on Okad a's NSR250 when I rode it. It's an Fl car-type flas hing light on the dash, but for '95 one so bri ght it sends a searchlight glare th rou gh the d a rkest visor to te ll your brain it's time to chan ge gear. Anyo ne who couldn't see this eve n in bright sun light wo uld have to have such d eficien t eyesig ht,. they should n' t be rid ing the bike in the first place! Just tap the shift lever w hen it flas hes, an d since you haven't had to back off the th ro ttle, one bit to cha nge up, you're still maximizing acceleration an d keeping the engi ne pulling as hard as it can. Of course, choosing the right gearbox r atio s is a key part of this process, an d w ith no less than nine possible choices for bottom gear, eight for . second, four for third, three for fourth an d five each for fifth and top, you can begin to appreciate how challenging an d crucial a function this is. En gine acceleration is the secret to the Aprilia's und oub ted edge in top-end p e r fo r mance over its Japanese riv als, and the sligh tly harsh-shifting gearbox is the key to unl ocking that. Though the RSV250 's chassis has 'f '!>. - ~- ~ .. -- "_. - essentially the same geometry as in '94, with a 21-degree head angle and the sa me relationship between swingarm pivot and steering head, not to mention the same wheelbase and the same engine location, it is in fact a new design, says Jan Witteveen, with different internal construction aimed at increasing stiffness at certain crucial points. The engine crankcases were also new, to create a stiffer structure, while the choice of tw o carbon-fiber swinga rms with different stiffness-toweigh t ratios used at the end of 1994 was aban doned in favor of a new aIloy swingarm, which was also reinforced internally co mpa red to the sim ilar design also used last seaso n. Aprilia was force d to ju nk the Ferrari Engineering carbon swi ngarms because of the time de lay involved in modifying them, says Wit te vee n . "You can' t just cut an d reweld it when you want to change something," he says. "Ins tead, it involves making new molds, w hich is m ore expensive and time-consuming, and is also why we don't use a carbonfiber chassis. The carbon swingarm wouldn't fit the new frame , and we also used larger-diameter axles than last year, so we'd have needed a whole new design which we couldn't later modify if we needed to. Anyway, we don't need to worry about saving weight like on the 400 , where we do use a carbon swingarm. The new frame was two kilograms (4.4 pounds) heavier than the old one, but we managed to save it elsewhere." Increasi ng stiffness was a p riority not in terms of pu ttin g the power down out of tu rns, as yo u might ex pect, bu t to (Opposite page ) Max Biaggl's championship-winning RSV250 fla nked by Its larger (the RSV400, ri ght) and smaller (the 125cc GP bike) bre th ren . (Right) Designed with the aid of a wi nd tu nnel, the low-drag fairing helps push top speed past th e 17Qmph mark. (Below) Extreme steer ing geo met ry makes th e Ap rllla lightning quic k on tu rn-In, but hamper s stab ility under hard braking. 1

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