Cycle News - Archive Issues - 1990's

·RACERtEST. Aprilia RSV400 ----------------------------- ering the only 500-dass twins I had ridden before were a serni-vintage TR500 Suzuki and 375cc TZ Yamaha - both parallel twins without balance shafts - that's not surprising. It's worth paying due credit to the man who put the ApriJia concept into operation first, though - German Hans Becker, who finished fifth as a privat~r in the 1991 World SOOcc Championship on his little bored and stroked TZ250 Yamaha and beat V-four machines on more than one occasion. But it's the combination of all this usable power and the sweet, responsive handling of the 250-based chassis that is so impressive - and addictive. You can stand the bike on its nose with the carbon brakes coming into a turn, flick it into the apex with lots of corner speed, and get hard on the gas much earlier than on a 500 V-four - and with heaps more confidence, too. You respect the Aprilia, but you aren't intimidated by it. In terms of size it still feels like you're riding a 250, with all the confidence from the agile handling that brings. The front end gets light and the bars wiggle in your hands as you accelerate hard down the short straight to the next MugeIIo chicane - Reggiani has the steering set up quite loose, but the bike "finds its own way just fine, and all those power wobbles aren't a problem in spite of the light weight.· Fork settings for the upside down Ohlins are quite stiff - but hit those br~es and you'll find out why: The Apalia's trump card is the turns, and how it brakes and goes around them. You don't want front-end dive as Aprilia RSV 400: Howandwhy_ he man behind ApriJia's onslaught on 500cc-class convention with their petite twin is chief race engineer Jan Witteveen, the man who delivered Aprilia boss Ivano Beggio tw~ World titles in both the 250cc class with Max Biaggi, and the 125cc category with Alessandro Gramigni and Kazuto Sakata. The commercial benefits in terms of Aprilia street bike sales that this GP success delivered, earned the Dutchman heaps of brownie points - explaining Beggio's decision to give the green light to a project Witteveen had personally coveted for several years: to develop a jumped-up 250 twin for the 500cc class. Bimota had the same idea back in 1990, but opted instead to build a high-tech, full 500cc, V-twin street stroker that will finally go on sale next year. That wasn't at alJ what Witteveen had in mind. "At the Donington Park GP in 1993 when aean-Philippe) Ruggia won the 250cc race on our bike," he explains, "he lapped faster than all the SODs except Cadalora, who won the race but was only two-tenths of a second quicker than the ApriIia. For quite a few years r d wanted to build a jumbo 250 twin for the 500 class and now that the lap times of the two classes had got so close, especially with circuits becoming slower and tighter, the time was right to T try." ~ 0\ ,...... C1'5' ,..-< I-< OJ "S ~ OJ o 18 The key to the project was the weight advantage offered by FIM rules to twin-cylinder bikes in the 500cc dass - a l00kg (220 pounds) minimum weight (actually, 215.6 pounds without the fuel tanIc. as GP bilces are now measured) compared to the l30kg (286 pounds) weight limit for the fours that are the class standard - and 95kg (209 pounds) for the 250 class. "The idea of a twin with more engine performance than a 250, but the same high comer speeds and braJcing advantages, became very attractive once four-cyUnder lap times stopped improving," says W1tIl!Yeen. "Nobody knows if there's a quantum timit to fiour-cyJinder perf0rmance, or if so, wf1at that is - bat it is a fact that even with the introduct:ioR of Big Bang engine technology which makes the bikes easier to ride, 500cc lap times have stayed essentialIy static for several years, in spite of better tires, bette£ suspension. and ongoing work by all the manufacturers. But 250 times have kept improving, so a jumbo 250 with a favorable power-to-weight ratio which still kept the same characteristics in terms of engine performance and handling had to be a viable option." A series of computer simulations using many different circuits seemed. to confirm this - so Aprilia embarked on the 400 V-twin project in September '93, and had a bike ready for testing six months later, having designed you trail brake into the apex - especially if you just finally managed to outbrake the V-four that has been zapping you in a straight line and getting in your way in the turns for the last few laps... But what you do want is to keep on riding the RSV400 until the sun starts to set behind the Mugello mountains - but worries about engine mileage meant just eight laps, only enough to be convinced what a serious role the Aprilia could play in assuring the 500 class's future. Aprilia's intention was always to sell customer replicas if the bike proved competitive, and that will surely be an option for 1997 - provided there's a market. The problem is that the GP privateers such a bike would be aimed at need to sell their existing V-four equipment to finance the purchase of an Aprilia - or Honda NSR500V - and and built it entirely themselves, with no input from their Rotax engine partners. When Loris Reggiani qualified the new bike on the second row for its first GP at Jerez in May '94, and finished ninth in the race, the Italian pocket rocket's real potential was confirmed. Or so it seemed... In fact, those Spanish GP points were the only ones the little Aprilia scored all year in its 1994 debut season. a rash of seizures causing the team to withdraw the bike from action after four races (in spite of the hefty fines they had to pay for no-showing under the loopy Doma/IRTA system), to allow them to concentrate on winning their inaugural 250cc world crown with Biaggi, and to develop new parts for the 400. "It wasn't only piston seizures we suffered, but a variety of problems we encountered once we tried to increase power which we needed new parts to cure," says Witteveen. "But to be h0nest, 1 thought we'd have more trouble than we did. Over last winter we considerably improved the whole package, with a new chassis designed specifically for the bike rather than a modified 250 frame, as well as 15-18 bhp more power than in '94. More importantly, we made the engine reliable - we had only one mechanical problem all season in '95, when a big end went in Donington." The result was a string of top10 finishes for Reggiani on the little 400, culminating with a glorious finale at Catalunya in 0ctober, when he got the better of a race-long duel with Scott Russell's works Suzuki. to finish seventh, showing that the Aprilia is now capable of competing with the four-cylinder works bikes, not just the privateer V..fours that had been its sparring partners in the early days. 'Though declining to reveal the engine's exact bore and stroke, beyond the fact that it's been the same from day cae of the project. Witteveen disclo!lI!S that the Aprilia's true capacity is 4lOcc, rather than the rumoured 38Occ, and that both cylinders have the same dimeDsions, not a diffaet,tial capacity as the GP paddock rumor mill has insisted. While following the same 9O-degrft V-twin rotary-valve layout as Biaggi's title-winning 250, with twin contrarotating cranks that remove the need for a balance shaft to eliminate vibes, there are no CODIIIlOI\ parts between the two engines even though they're interchangeable, thanks to identical engine mounts - the 400 crankcases have to be stronger, to cope with the extra power, and of course cytinders, heads, pistons, rods etc. are obviously different, though without using any exotic materials like titanium or ceramics. In that case, why not build a full 500, as Honda has now opted to do after deciding to follow Aprilia's lead with their new NSR500V V-twin? "It was important for me to keep the same characteristics as a 250 in terms of power delivery, handling and, above alJ, revs," says Witteveen. "I decided on 410cc from the very beginning as the maximum engine capacity which allows this to be done - any bigger, and to achieve reliability you must lose revs because 01 piston because there are no National 500cc Championships anymore, there's no second-hand market for five-year-old ROC Yamahas. But the new V-twins could yet turn a page in 500cc class evolution: Buying and maintaining a V-twin 500 would be no more expensive than running a kitted superbike - in which case, here is also surely the basis for European and Japanese 500cc Championships, which in turn would have the benefit of providing a nursery for 500cc GP riders of the future. GP privateers and budding Mick Doohans alike would find a Vtwin like the ApriIia cheaper to buy, less costly to maintain, easier to ride and above all more fun to compete on than a four-cylinder bike. Aprilia has invented a new kind of GP motorcycle - but remember, its seriously addictive. fN speed and reciprocating weight, which stops it being like a 250 to ride. Also, 1 believe 410cc is the break-even point for horsepower: Increasing displacement would bring more torque, but not more power - only one or two bhp more." Though 3000cc Formula 1 car engines now rev to 16,400 rpm in 10-cylinder form, the Aprilia's piston speed has now surely broken the 25-meters-per-second barrier reliably - a COlISiderable achievement. In its present form the 410cc motor is safe to 13,000 rpm, and delivers 129 blip at 12200 rpm at the gearbox, running on the same 39.5mm Dell'Orto flat-slides without powerjets as the 250 - comp8ft!d to around 180-190 bhp for the works V-lours weighing 66 pounds more. Aprilia's next step this past season - once they got power up and the engine reliable - was to start trimming weight from the 108kg (237 pounds) form in which the bike raced in '94The engine actually weighs the same as Biaggi's 250, says Witteveen, because the smaller bike meets its own class limit easily, so for example they use aluminium crankcases whereas the 400' s are magnesium,. thus scaling 1.8 kilograms (3.9 pounds) less in spite of being beefier. So the 5kg (11 pounds) weight difference between the two bikes comes down to the chassis, which" though the 400 has a -longer Swingarm to help keep the front wheel on the ground, share identical geometry and the same wind-tunneI-developed bodywork. A constant flow of lightweight parts like the beautifully crafted combined carbon-fiber swingarm and rear fender, or the Ferrari Engineering carbon-fiber wheels, down to such attention to detail as a smaller body for the rear Ohlins shock, gradually pared the weight down to close to the l00-kilo (220 pound) mark, which Witteveen. says the bike now meets, depending on the tires chosen: Thicker carcass tires can raise the weight by a kilogram or more to over 101 kilograms! So after two out of the three years Aprilia boss Ivana Beggio gave the 400 project to prove itself, how does Papa Wrtteveen feel about bringing up Baby: pleased, satisfied, or disap=? . "I'm honest1y with what we've achieved so far - 1 thought we'd have more problems getting competitive power reIiabIy than we have. We're exactly where I hoped to be: The fust year was supposed to consist of finding out the pnlb'ems, the second of resolving them and getting competitive horsepower, and the third of getting n!!lUIts - that's why we used Reggiani, who's an exce1leDt development riders for the first two seasons, and have signed (Doriano) Romboni for next year, though I hope Loris wiD still be with us as second rider, stiH in a de.efopment role. 1 didn't expect the wheeIie ~ and this is a crucial factor not only during the race, but especially at the start The bike is very hard to get off the line without losing time having to back off when the wheel comes up, that aBows the fours you outqualified to beat you into the first tum, and then you Ilave to spend the ~ of the race getting past them. Our goal is to have the same usable acceleration as the fours, !lO we can stay with tbem in a straight line and then use our superior braking and cornering to get past them. With 140 bhp we'll be able to do this, and 1 believe we can have that reliably in '96 by exchanging some of our excessive midrange power for more top-end performance.Our bike is already quite fast· 308 kph (190 mph) at Mugello - but the problem is getting there, in terms of acceleratioa. We can surely resOlve this - and Honda's decision to foHow us by building a twin for the 500cc class has made us want to try even harder!"

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