Cycle News - Archive Issues - 1990's

san" - would have approved : that' s exactly the kind of David and Goliath story come true that he appreciated, and the fact that it came about b y doing th ings di fferently fro m everyone else wou ld have tickled him ev en more even if it was Honda that was on the receiving end. . For Aprilia's wo rld title wa s not only a testament to Biaggi's ruthless determination an d combative skills, it also justified Witteveen's faith in the rotary-valve engine layout, which hadn't won a world ch am p ionsh ip sinc e 1981 - the fina l crown for Kawasaki's tandem-twin 250 . Reed valves rule, ok ay? Not any more: Aprilia's convincing su p rem acy this season - Biaggi won five races out of the 14 GPs run, but fell off with victory in sigh t in three more - has almost certainly turned a page in 250 class design. Now it may no longer be acceptable for the Japanese to transfer technology from the 500cc cla s s - where the way th e power is delivered is more important than chasing horsepower figures - to the 250s (and, by im p lica tio n, th e 125s as well ). Reed-val ve e ng ines ha v e a smoothe r po wer delivery, but rotaryvalvers - and Aprilia is the only factory to use this layout - give more pow er, and in th e s m a ller capacity classe s that's what matters mo st , as the stra igh t-line supremacy of Biaggi's RS250V down the . front straight at Barcel on a lap after la p demonstrated. Okay, part of the rea son for that was Biaggi's mega-drive out of the fast last tum, but you don 't whistle past a works Honda in a straight line just by riding hard . Max had power in hand and it showed . You can 't be in two pl aces at once, and when Aprilia arranged their annual press playday for the same time I was on the other sid e of the world in Australia riding 'Scott Russell's Kawasaki and the other top-contending bikes from th e World Superbike series - a se ries that Aprilia is all set to join come 1996, with their V-twin four-stroke n o w und er development - it seemed I'd miss out on the chance to ride the Italian factory's 250cc world champion. But just before Christmas, Aprilia rented the Vallelunga track near Rom e to give me a private test session with mighty Max's megamotorcycle coincidentally ju s t a co u p le of weeks after I' d ridden the bike that finished s eco n d in the w orld ch a m pionship, Tadayuki Okada's works Honda NSR250. It's hard to think of two more contrasting bikes in modem-day GP racing . In previous years, Aprilia has spe nt the whol e season playing catch-up after a major redesign mad e ne eded time to come good. Not in 1994: After introd ucing an all-new, sma ller-crankcase engine in '93 that, whil e retaining the distincti ve twin -crankshaft rotary-valve forma t, was 4.4 pounds lighter and had a different crankcase water-cooling layout - cru cial w hen the twin 39.5m m Dell 'Orto flat slides, sti ll withou t any powerjets, spi t mi xture directl y into th e cases via the carbon -fiber rotary valves - Aprili a played safe for the new season, changin g only the cran ksh aft design , igniti on and th e (u p d a te d) W P s us pe nsio n . Th at meant retaining th e electronic p ow er val ve in tro duced on the new engine which, link ed to the posi tion of the carb slides as well as the tachometer, offered more precise control over the guillotine va lve in each five-tran sfer I threeexha us t-port cylinder, com pared to the distin ctive pneumatic po wer valves used on the Rotax-built engine before - at the expense of a 4.4-pound weight penalty th anks to the electric mot or needed to drive the sys tem. But becau se the new, m ore compact e ng ine d es ign wh ose Aerodynamics refined over the length of the season and narrow-section tires helped to push the top speed of the RS250V past the 17o-mph mark. shorter dimensions enabled its location in ch assis d esi gner Ga etano Cocco' s beautiful twin-spar fam e to be optimized, that weight penalty was cancelled out. Aft er early problems refining the new ignition system, Aprilia finished the '93 seas on strongly, w ith Loris Regg iani outscoring everyone else over the last six races en rout e to third place in the cham p ionship. Biaggi picked up in '94 wh ere he left off, winning the first two GPs in Au stralia and Malaysia to establish a crucial early dominance which meant that it was H onda (and Yam aha ) who we re playin g catch-u p this time, not Apri lia. It staye d tha t w ay, too . There was a further crucial reason for this: the new low-octane fuel regulations in trod uced last season, which affected A p rilia far less th an th e ir reed -v al ve riva ls. Designing new curves for the progra m ma ble d igital ig nition, as well as detail changes to the combustion cham ber an d exh aust pipe d esi gn, swift ly claw ed back the 5-bhp power loss tha t th e n ew fu el in itially en ta ile d , while th ei r Japa nese co m petition we re s till struggling to do the sa me thing. Aprilia then ad d ed insult to inju ry by fu rthe r eng ine developmen t during the season, findi ng a vital extra 3 bhp just befo re the crucial Cze ch GP, tha nks to re vi sed cy li nder p orting, exhaust d esign a nd co mb ustion cha m be rs w hich enab led Max to win the race and establish a decisive championship lead . By the end of the year Witteveen had extracted "over 95 bhp" from the engine at 12,800 rpm in fac t understood to be 97 bhp, There' s good chance we 'll see the first 100-bhp 250 in '95. Nothing comes free, though , and 'this ex tra punch of titl e- winn in g power is on ly d eli vered over a sma ll ran ge of revs, betwee n 12,000 and 13,000 rpm. 50 th ou gh th e engine pull s clea n ly a n d strongly from jus t under 9000 rpm, and comes on the power smoo thly an d wi th a lot of low-rpm and midrange punch, it isn' t till the tacho needle hits 11 gra nd tha t you ' re in to w orld cham pi ons hi p warp-factor mod e, and it' s best to keep it revving eve n high er . Given the ro ta ryvalve motor' s tr ad iti on al appetite for revs, th is is not dif ficult, but thi s ye ar there's no lon ge r any point in bu zzing the engine to 14,000 rpm unless yo u rea lly have to in orde r to save a gearcha nge, beca use p eak p o w er starts to tail o ff between 13,000-13,500 revs. Co mpacting the p owerband in this way in pursuit of more bh p h as now made the poin t a t w hich yo u change gea r on the Ap rilia mu ch mor e crucial than in the past, hen ce the int roduction of a gizmo borrowed from the racing car world, which only John Britten has used on a race bike so far: a bright red strobe ligh t next to the rev counter which flashes at 13,000 rpm on th e Ap rili a to tell yo u the po we r has peaked and it's time to change up. When you're rubbing han- dl ebars with Capirossi & Co. peering at th e tacho needle is a lu xury you can't often afford, and because th e V-twin rotary- valve motor is so free-revving. it's hard to know wh en best to sh ift gear just by engine feel. Good idea, 50 too is the incorporation of the speed-shifter mechanism that Aprilia was the first to fit to a wor ks GP bike inside the gearbox casing. instead of being tacked on externally as an aftert hought where it' s always ready to get shorted ou t in the rain - I know, it's happened to me in a race, Th e gea rshift is smoo th er and less notch y than before , too. But the way the Aprili a jumps out of turns reminds you that in spite of the lower octane fuel. Witteveen has been able to retain the same very high comp ression rati o as be fore actu ally 17.5:1 on the bik e I rode, even higher than on the Japanese bikes and an aid to na rr owing the initial acceleration gap out of turns which is now apparently the only h andicap the Italian bi ke has against its Japanese reed -valve rivals. Without Okada 's bike th ere on the track in front of me at Vallelunga, it was im possib le to comp are p erform ance d ir ectl y, but I ha ve to say th e Aprilia definit ely has a brusqu er power delivery low down than I remember, and certainly more so than the Hond a I' d been rid ing a few days before at Suz uka . Let the . revs d rop into four-figure mode, as is practi cally in evitabl e round the tight Vallelu nga infield , and yo u h ave to be prepared for the back whee l to sna p out of line and the bike to shake and squirm as that near -l00-bhp ge ts downloaded to th e ta rm ac as yo u hit th e tru e pow er band. Fra nkly, yo u've no busin ess let tin g th e revs d ro p tha t low unless it' s unavoid able like at a hairpin or suchlike, makin g it eve n more vital than eve r that yo u've chosen the right set of rati os to su it the circu it, so you can max out perfor ma nce by shifting gea rs to keep the e ng ine always turnin g in th at 12,000 -rp 13,SOO m optimum pow erband. When you co nsider tha t th e works Aprili a rider has a choice of no less than nine p ossible ratios for bottom gear, eight for second, four for third, three for fou rth and five each for fifth and top, then you begin to understand how difficult but also how crucial it is to ge t your gearbox set up properly. It says a lot for . Mighty Max that he won his first two races back on the Aprilia - after a year away racin g the Honda - on tight, technica l circuits where gearbox ratios were crucial. Not jus t a cool dude, but a clever one too. ' . But ge tting you r act togethe r to start cha nging gea r w hen th e light fla shes isn't as easy as it so u nds, because the Aprilia revs so freely and picks up revs so fast, the tach needle's almos t always a t 13,500 rpm before you ' ve ha d th e chance to tap the shift lever ligh tly to hit , th e next gear up . Th e 'RS250V engine accele ra tes n otabl y quic ke r th an th e Ho nda, even if it isn' t so sweet and wellmann ered in the low-down power deli very , Bu t when yo u h it fifth a n d then sixt h gear at 13 gran d-plus, it' s like hit ting boost on a turbo. Phew! Th an ks to thei r wi nd tunnel-d eveloped new bod ywork introd uced at Jerez once the GP circus came to Europe, and refined into its pr esent guise for the following ra ce in Aust ria , th e Ap rilia's u ndoubted power ad vantage was tra nslated into an edge of top spee d that go t greater still by the end of the season. Top speed was furth er aid ed by the ra m-a ir effect of the air duct located in the right s ide of th e n ose, feed ing th e s lig h tly pres surized a irb o x for th e tw in Dell'Ortos, fina lly bored out a littl e by the end of the season to 39.5mrn. Biaggi's tucked -in ridi ng sty le also helped a lot,

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