Cycle News - Archive Issues - 1990's

"My goal now and surely Honda's too, is to get 100 bhp from a 250 GP engine," he says. "1 believe we can get there in two years from now, which frankly will make our bikes almost as fast on many circuits as the factory 500s. Biaggi was 12th on lap times in the 500cc class at Kyalami, ahead of all the privateer bikes." So there's hope for Bimota's 500 V-twin fter all - and maybe it'll be joined m a couple of years by an Aprilia 500 V-twin... ? Judging by Witteveen's smiling no-comment, don't bet against it! Riding the brace of factory Aprilias gives a vivid impression of performance and acceleration, especially compared to their sluggish Italian Gilera rival, which I'd ridden only a couple of days before. Compared to the newer Gilera, which has a great chassis but a sleepy motor, the Aprilia is infinitely sharper and more responsive on the throttle, even though there's no powerjet on the Dell'Ortos and no computerized gadgetry to link up operation of the powervalve, throttle position, ignition curve and gear selected. Instead, the Aprilia is living proof that, well - simple is best. Dialling myself in to the wet conditions on Reggiani's bike entailed a couple of laps of playing with the throttle, till 1 overcame any concern about decking the bike in one of Mugello's mini-rivers and got on with the job in hand. Backing off the gas, then corning on it hard again showed not only how well set-up the carburation was low down, but also how forgiving and tractable the engine is - and it's a disc-valver! Unlike even five years ago on the Rotax tandem-twin the Aprilia is effectively descended from (though 80% of the V-twin engine is now made in Italy), you'd never have expected such a wide spread of power or so smooth a transition into the strong powerband with a rotary-valve motor as the Aprilia now provides. Such is the measure of Witteveen's feat - he's made a disc-valve engine which actually has a wider spread of power and is better at low revs than Honda's title-winning reed-valve NSR 1 was riding only two weeks beforehand. No wonder the hot rumor we picked up in Japan is that Honda actu!,lly has their own rotaryvalve 250 under development for 1993; if you can't beat 'em (and by the end of the '92 season, Honda couldn't), join In its spec sheets, Aprilia claims its AF1250V produces 84 horsepower at 12,500 but the bikes actually produce a lot more than that. The rotary-valve twin features 39mm Dell'Orlo carburetors mounted on top of each other on the right side of the engine. 'em. "Sure," says Witteveen unconcernedly, "if you're going to build a 250 or especially a 125 to win GPs with and don't have to take anything else into account, of course you'd choose a rotary-valve design, because it will always produce more power than the equivalent reed-valve engine. But the Japanese teams all run their 250 GP programs as spin-offs from their '500cc class development, where on a 170 bhp-plus V-4, the trick is not to get more power, but to put it on the road. That is why they all use reed-valve engines for their 250s, whereas ideally they want a rotary-valve design - same thing with Gilera, who made a 250 thinking about a future 500. We don't have to worry about that, so we use what's best, and that's a rotary-valve engine which we've gradually refined to be both reliable and more tractable. lf Honda changes to follow us, they're only recognizing the inevitable!" Aprilia just rockets out of turns with really impressive acceleration, but while .Chili's bike was really stable on the gas and put the power down well without getting out of shape, Loris' machine got as squirrelly in the wet under hard acceleration as I remembered his '91 bike had in the dry when I rode it on the same track a year ago, and the reason is the same. Because of reduced mobility thankS to his catalogue of injuries over the years, Aprilia have made Loris an allowance by enabling him to set the bike up with extreme steering geometry - a 21-degree head angle (Chili uses as 22-degree setting, thanks to the adjustable yokes) and just 78mm trail. This means Loris can wedge himself in place and use body Latin to change direction, which is all very well till you have to cope with such a twitchy bike in the wet, where smoothness and predictability are the preferred handling traits. That made Chili's bike far more enjoyable to ride quickly on, same as in the dry last year, especially with his 500class derived riding position, with wider-spread bars and more space to move around on the bike. Frankie's Aprilia was noticeably more stable on Mugello's several fast sweepers, though the reduced amount of weight on the front wheel didn't cause any alteration in my heart rate on the trio of off-camber downhill turns - Mugello must have more chances to lose the front wheel per lap than any other track besides Zeltweg. The great grip from the Dunlop wets, even as the track started to dry out, gave lots of confidence too but it was the really predictable feel of the Gaetano Cocco-designed '92 chassis that really heightened the feel-good factor. Compared to the Cadalora Honda, which had leaped about a lot on Suzuka's bumps and dips, the Aprilia was ,so poised and stable, perhaps a testament to the excellent setup of the White Power suspension package, as well as' the increased stiffness Cocco dialled in to the '92 frame with his new swingarm design with its twin curved arms, the one on the right bracing the straight main strut on the chain side. Chili's bike felt better suited to the wet as well because the rear suspension was more softly set up, giving excellent tra~ tion and a neat little wheelie every lap as I twisted the wrist out of the second chicane. Reggiani's bike ought really to have been fitted with the White Power semi-active suspension the Dutch firm are developing together with Aprilia, which uses sensors on the throttle and front brake to stiffen or soften the rebound damping respectively on the rear shock, via an electric motor which alters the damping valving: under braking, rebound is softened to promote longer shock extension, while on acceleration it's hardened, to reduce rear-end squat. Loris can adjust the operating range via a knob on top of the fork yoke, but sadly this wasn't fitted to his spare bike which I was testing, only to the one he was playing with himself. at the same time. Having converted the right-foot gearshift Loris still uses to t!:te left side (they must think none of us hacks ever ride historic race bikes!), Aprilia had . also been forced to disconnect the Tellert CTS slick-shifter they adopted on Chili's and Reggiani's bikes since the middle of the season - Biaggi declined to use it, after breaking five gearboxes try- 33

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