Cycle News - Archive Issues - 2000's

motor definitely makes using the ic behavior under acceleration, than higher gear a better option. its rival from Bologna. This illustrates well how big an improvement the made-over V-twin I enjoyed riding it very much - and I was impressed how little gear-shifting I motor is over the previous version, needed to do in order to go almost two because the Aprilia now accelerates seconds faster on this year's b\ke than much better than before, and is more rideable in tight turns such as abound I did in identical conditions on the same circuit with the Aprilia one year at Valencia, thanks to the smoother ago. It's a flexible friend with a mile- pickup from a closed throttle. It still wide powerband spanning well over doesn't have quite the punch lower down that a Ducati has, and I would 6000 rpm, making this - gotta say it again - such a rewarding motorcycle to imagine that, at a circuit like Assen ride hard, when combined with that with all those third- and fourth-gear peerless chassis. banked turns where you need an And also, it must be said, a very engine that has muscular pull down serious contender for the World low, this must be quite a disadvaneither way, the wide-open powershifter works faultlessly in all the than shifting back and forth between the bottom two gears for extra punch, upper gearshifts, just not that one. This makes using second gear preferable wherever you can, rather as Bayliss does on his Ducati. I tried riding it both ways, and the flexible but potent nature of the '01 Aprilia ~Ihl®mt=~lbr®lli(!; ~TID1])(!;~ITil As in previous years, Corser's 2001 Aprilia Superbike was based on the limited-run RSV Mille SP, of which just a single batch of 150 examples - the minimum quantity needed to homologate the model for World Superbike racing - were manufactured in 1999: no more have been built since. Compared to the volume-production RSVIOOO, the Mille SP is in many ways a quite different motorcycle, with a more sophisticated chassis design liousing a special shortstroke version of the Aprilia 60-degree V-twin engine, which is only used on this model. So whereas the volume-production RSVlOOO's Rotax-built 998cc 'otto valvole' engine with chain-driven DOHC measures 97 x 67.5 mm, to produce its race-orientated Mille SP Superbike sister Aprilia employs a short-stroke 100 x 63.4 mm 996cc engine developed in conjunction with Cosworth in Britain, with a potential appetite for higher revs to deliver the power that wins superbike races. Ducati came to the same conclusion a year ago, and followed Aprilia in developing the Testastretta engine using the same short-stroke dimensions. which powered 996R-mounted Troy Bayliss to the World Superbike title this year. But Aprilia had the idea first, and together with the bigger bore come oversize titanium valves, fitted with single valve springs compared to the double ones used on the RSVl 000 ~treetbik~, for. the reduced inertia which permits higher revs. These are operated by a paIr of cham-driven DOHC race camshafts per cylinder, and set at a flatter included valve angle of 30 degrees, compared to the stock RSVlOOO's 32 degrees. Similarly, to reduce friction, the forged 12:1 Wiseco pistons are of a two-ring design, which Aprilia race chief Jan Witteveen says don't entail any oil blow-by problems, fitted via titanium rods to a nltrided crank. The SP Superbike's Cosworth-developed cylinder heads are quite different from the stock RSVIOOO design, with the larger valves necessitating a single central sparkplug instead of two, plus revised porting and a smaller combustion chamber, which incorporates Cosworth's trademark five-axis machining process to optimize turbulence and cylinder filling, aided by inlet ports which for this purpose are quite straight. The lower crank-driven counterbalancer fitted to iron out the vibration of the narrow-angle V-twin engine on the street RSVlooo is still retained on the works Superbike, but the road bike's secondary balance shaft mounted on the rear cylinder head has been junked, in pursuit of a little extra power at the expense of some increased vibration. The superbike's Mille SP engine employs sandcast-aluminum crankcases rather than the RSV1000's diecast ones, aimed at increaslng strength and rigidity at the cost of a slight hike in weIght which is partially offset by the magnesium side covers, while the cylinder design is a stiffer closed-deck format, compared to the RSV's open-deck design. But the dry-sump engine's bottom-end design is the same as on the stock Mille, with a lightweight, external, stainless-steel oil tank low down on the left side just forward of the engine, albeit with an uprated lubrication system featuring a second return pump. However, there's still no provision for an extractable six-speed gearbox on the Aprilia, as was first envisaged, for fear of reducing crankcase rigidity with the vertically-split engine: the race team has to open the engine to change internal ratios - a three-hour job which they don't have to undertake too often, since based on their 2000 race data they can design a gearbox for each circuit which is factory fitted at preparation stage_ The dry slipper clutch is adjustable for the degree of slip and incorporates a conventional rear-wheel cush-drive. thus quite different from Aprilia's patented PPC pneumatic system employed on the street Mille. Engine development in the past 12 months has focused on enhancing inlet design and airflow, coupled with optimizing the operation of the SP racer's Marelli EFI - for co,,:,pared to the single-injector 5lmm throttle bodies used on the RSVlOOO's Nippondenso fuellOjection, the Aprilia Superbike runs an Italian engine-management system homologated in accordance with World Superbike regulations via a 50-off customer race kit. featuring bigger 60mm Dell'Orto throttle bodies with twin injectors per cylinder - one in a Formula I-type extemal location directly above the intake trumpet, the other positioned just after the throttle butterfly. Added refinement to the top-end package has brought improved rideability as well as more power at higher revs, with the ApriJia's 60-degree V-twin motor now producing l71 hp at 12,200 rpm at the gearbox - up 6 hp on the previous season's bike, but with a much wider spread of power, and an extra 500 rpm overrev beyond that. A key factor in this improvement has been the ongoing development of the twin-pipe Akrapovic exhaust system, now entirely made from titanium and fitted with carbon cans, with the rear cylinder's exhaust Superbike title in 2002, with someone tage - must be why the Aprilia has never shone in Holland. But, if any- especially as he already has a season thing, it's stronger than the desmo- of racing a V -twin Superbike under his with Haga's 'grinta' aboard the bike - quattro in that all-important midrange belt, from his days riding a privateer sweet spot - and it also feels a little Ducati in the All-Japan Superbike more poised, less brutal in its dynam- Championship in the mid-'90s. CN header sharing the hole in the swingarm behind the engine with the Ohlins shock, and that of the front cylinder intruding through the center of the not particularly large, but quite deep, water radiator. The Aprilia engine must still be thermodynamically quite efficient in order to produce so much power with such a relatively small single radiator. though the oil cooler beneath it is quite big, and a bigger water radiator was fitted for mid-summer in Califomia, and Italy. While 20-percent stiffer than the stock Miije frame for the same weight, the SP Superbike chassis has an adjustable pivot at the rear for the heavily braced twin-sided swingarm, which the team .continues. to experiment with, In search of optimum traction. The Aprllia uses the latest desIgn of Ohhns shock at the rear, while up front the new 42mm Ohlins pressurized gas forks are fitted. "All forks go up and down and these pretty much seemed the same as the ones before, except they're much easier to adjust," says Troy Corser. "They're most sensitive to oil level that made a big difference to the way they worked. " Corser prefers a more balanced chassis setup, with a longer swingarm, slightly wider head angle, less offset and lower rear ride height - and this proved to work so well in optimizing the Aprilia's fine handling that 500cc GP refugee Regis Laconi ended up largely adopting it, too. Chassiswise, the Mille SP continues to be the only Superbike racer on which the position of the engine within the chassis can be altered to optimize weight distribution and handling 5mm up or down, 2mm forward or back, just as on Aprilia's GP two-strokes. In fact, Aprilia did try lifting the engine at the start of the season compared to 2000, in an effort to improve changing direction with Corser's preferred kicked-out chassis geometry, which Laconl also ended up largely adopting. "' tried it their way, but went back to the original location for the motor," says Corser. "Having the weight lower down makes it more stable over bumps, and I thought it flicked better from side to side in a chicane that way, too. But it was good to have the choice." Thanks to copious use of carbon fiber, lighter throttle bodies, and especially the adoption of OZ wheels each saving more than a kilo of unsprung weight, Aprilia has succeeded in trimming the 8.8 pounds over the minimum World Superbike weight limit which the 2000 Mille needed to go on a diet to lose - but in doing so, did not sacrifice the bike's excellent weight distribution by V-twin standards, with a 54/46-percent frontal bias thanks mainly to the compact mass of the 60-degree motor, which helps glue the front 16.5-inch Dunlop tire to the track. Twin 320rnrn Brembo discs were usually fitted up front, gripped by the Italian firm's latest radially mounted four-piston calipers, and were fitted for our Valencia test. But for some tighter circuits without constant very heavy braking - ironically including Valencia, and Kyalami - Aprilia normally uses smaller, lighter 305mm rotors, to reduce the gyroscopic effect and speed up handling. They have to be careful, though: combinlng the lighter brakes with the smaller radiator now brings the bike 2.2 pounds below the minimum weight limit, requiring Aprilia to break out their stock of lead bars to redress the balance. Visually speaking, the Aprilia still looks quite the most voluptuous - okay, bulbous machine on the superbike grid, a fact reflected in the bike's aerodynamic qualities, for the stock Mille SP is the first production streetbike to break the benchmark 0.30 Cx barrier in wind-tunnel testing. "People say It looks porky, but it doesn't feel that way when you ride it, and in fact we've got it steering a little better than the narrower Ducati," says Corser. "I reckon it's a visual deception caused by the color scheme, which makes it look wider than it really is, especially at the front. And for sure you can tuck away better behind the screen than on the Duke, which probably explains why our top speed isn't too bad." Ducati engineers and riders will concur, claiming that the Aprilia is actually faster on topend speed than the title-winning 996R. Now it has to prove it's faster everywhere else as well. in 2003. cue' e neVIl's FEBRUARY 20, 2002 23

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