Cycle News - Archive Issues - 1990's

Bimats DB4 (Left) The single PaloU shockworlcs without a linkage. (Right) Despite being fitted with a pair of 38mm Mlkunl carbs, Blmota claims the 904cc Ducati powerplant makes 80 bhp, the same number claimed by Ducatl for Its latest fuelinjected version. o .... ~ '" ~ l! {f 16 pounds - 6.6 pounds less than the steelframed DB2 - makes this a bike for twisting country roads rather than fourlane superstradas. Topping out at 8000 rpm and safe to nine grand (strangely with no rev limiter on the test bike's Kokkusan ignition), there isn't really any point in revving the desmodue V-twin that high, because the last 1000.rpm are a real struggle, and it's much better to ride the torque curve and change up at around 7500 rpm, reveling in the meaty acceleration that even this humble power output delivers in such a light bike. Whack the light-action throttle open in the bottom two gears and you may find you need to stand on the footpegs to force the front wheel back down to the ground again. But suspicions that the Bimota is undergeared were flat out confirmed on the Ancona autostrada. The DB4 had to be coaxed up to an indicated 121-mph top speed, and it resolutely refused either to break the 125-mph mark or to pull any more than 8500 rpm in doing so. This is pretty disappointing for a 900cc desmo V-twin, and it indicates not only that the 38-tooth rear sprocket fitted is too short (the DB2 used 37T and the Mantra 36T), but also that airflow to the carbs (Brmota uses its own airbox design), the jetting, exhaust design or aerodynamics, either singly or in combination, need further development. Or just sacrifice some of that more-than-adequate acceleration and gear it up a little to restore some of that missing top speed. However, that's almost irrelevant, for two reasons. The first is that Bimota is conscious that the DB4's power output is pretty humble by its own standards, and in a departure from the Italian company's previous policy, it is presenting it as an entry-level performance bike that almost any owner will want to wbrk on - this happening eitl\er at his friendly local Ducati tuning house or with Bimota's own forthcoming aftermarket catalog. With the world's leading desmodue tuning house, Vee Two Australia, already associated with Birnota after the two teamed up to win the '96 BEARS World Series with the Vee Two DB2R, there's little doubt that stuff such as Vee Two's camshafts, oversized valves, ceramic-coated high-compression pistons, downdraft cylinder heads, flatslide Keihins .and Carrillo rods will end up in many of the DB4s sold, pumping up horsepower to 100 bhp and even more. This bike is a great base for doing so, because of reason two: The DB4 chassis is more than capable of harnessing the extra performance and, even in the· stock bike's underpowered form, delivers smile-a-minute handling that belies the bike's humble power output. Paradoxically, it's because it's relatively underpowered in relation to the frame's capabilities that the DB4 is so much fun to ride. The sweet-handling chassis package encourages you to brake late and keep up corner speed, maximizing the handiing potential in pursuit of maintaining momentum. On a switchback strip such as Pesaro's Strada Panoramica, with the Adriatic Sea on one side and the Appenine mountains on the other, you discover the hidden sportbike properti.es that were locked away in the Mantra's nimble-handling oval-section alloy frame, with its light build and short 54.3-inch wheelbase. This chassis carries tne 90-degree Vtwin engine quite low, without affecting ground clearance - even with the grippy Pirelli Dragon Corsas fitted as stock (the first time Pirelli rubber comes as original on a Bimota), reflecting the Italian tires' significant improvement ·in grip and wear in recent years. Scraping the footrests or decking the fairing on the OB4 just doesn't happen, even at extreme lean angles. Yet the low center of gravity delivers excellent stability around fast, bumpy turns. It's better than the OB2, which can get a weave cn when it hits a bump cranked over under power. The steering is beautifully weighted, allowing you to flip the bike from side to side so easily through a series of turns, yet it also tips with control and p.oise into the apex of a bend. Certainly this also comes from the DB4's steering geometry, which, though based on the OB2, is subtly altered from Marconi's original design, with the head angle reduced to 23 degrees and trail to 91mm via bigger offsets for the 43mm Paioli forks. This makes turn-in even easier on the DB4 than on its Rimini-built desmodue ancestors, yet it's achieved w1thout making the bike nervous or unstable, even under heavy braking. There's lots of feel from the big 320mm Brembo cast-stainless rotors and their latest-generation four-pot calipers that more than lived up to expectations, with good bite plus a sensitive response from the adjustable lever. The Paioli suspension was very much on the stiff side for the first of my two days on the bike, but softening it all around at our overnight stop delivered superior response from the Paioli front end, even though this is only adjustable for preload and rebound damping - not for compression. But even over inland roads ravaged by winter frost, the DB4 felt well-damped up front, though perhaps more surprising still was the superior ride quality on what i such a light motorcycle, especially with its relatively unsophisticated cantilever rear end. The. PaiaH rear shock is fu 11 y adjustable, and it works well with the sticky 180/55 rear Dragon in putting the power down out of turns - but the way it shrugs off any bumps you encounter while doing so, leaned over on the angle, is truly impressive. Kayaba's European suspension partner gets better and better at delivering a well-sorted ride - and don't forget PaioH's HAT race division won the World Supersport title in '98 with the Alstare Suzuki team, so it knows how to dial up compliant sportbike suspension. The DB4's riding position is uncompromisingly sporty, with a tall rear ride height that shorter riders will need to tiptoe over when hopping aboard. On a Bimota, this has the usual consequence of pushing lots of body weight onto your arms and shoulders. This only becomes a problem when riding the bike slowly in traffic, at whicl1 point you also start to notice the trademark heavy operation of the Oucati clutch. But at speed on the autostrada, the pointy shape of the DB4's screen does a surprisingly good job of giving good protection w.ithout undue turbulence, which, combined with the shape of the shroud covering the .5.3-gallon nylon fuel tank tha t· allows you to rest your chest on it when crouched down low, lets you ride the bike clo e to flat out for mile after mile without di comfort. The OB4 does seem very slim and lean when you sit on it - much more so than the new Ducati - whicl1 in turn adds to the impression of agility and nimbleness that is confirmed when you ride it. Yet the fairing also gives good protection, without being bulky: Massimo Giovagnoli did a good job in designing it, though I must say I'd prefer the lower half to be painted white like the rest of the bike, rather than the so-practical but so-leaden black belly pan which, frankly, spoils the aesthetics. Like the bencl1mark DBl, the DB4 prototype was all white when I first saw it last May, and it looked lighter and even leaner as a result. And apart from my friend Ferruccio's tip about the mirrors - okay, they don't vibrate at speed, but even pulling your shoulders in doesn't let you see flashing lights behind you (that's my excuse, anyway!) - I also think it's a shame Bimota had to use the Yamaha head lamp from the YB9, which makes the DB4's "face" look a bit anonymou~ and dated, though with homologation taking the time it does and costing so much, there was probably no other choice. Still, its beam is powerful enough to get the attention of a Croatian truck driver who's about to pullover on you on the autostrada at a closing speed of about 75 mph, so I guess it works okay. The same thing goes for the whole bike in terms of looks, handling and midrange performance, and with Ducati's predetermined decision to move its desmodue sportbike range away from its traditional customer base in search of new buyers, it has left Bimota with the chance to move in and create a handmade, harder-edged V-twin with lots of tuning potential thanks to its carbureted configuration, to fill the gap at an accessible price. The 0B4 is the result, and Francesco Tognon must be hoping it has the same effect this time around as its DBI ancestor did. History will tell. CIII Bimota DB4 Specifications Engine , ... ,Air-cooled SO-degree V-twin II......... ..... _ ... w/ two valves per cylinder Bore 92 x 68mm Displecem.nt ... , .. S04cc Comp.....ion ratio . . _.9.2:1 Carburetion (2) 48mm Mikuni Ignition .. Kokkusan electronic Ho....pow.r , .. 80 bhp @ 7000 rpm Transml••ion .. , 6·speed Fra , Aluminum oval-tube trellis W lbe.. . .... 53.9 In. Rak./trail . .23°/91 mm Seat h.ight .... _.31.5 In, Suspension Front .,...... ' .43mm Paioli fork w/ spring-preload and rebound· damping adjustment; 4.7 in. travel R.ar . , .. , .Single Paioli fully adjustable shock; 4.0 in. travel Wh..../tI.... Front Antera 3.50-ln.-wide wheel wi 120170ZR 17 Pirelll Rear ,Antera 5.50-ln,-wlde wheel wi 180/55ZR 17 Pirelli Brakes Front , ... Dual 320mm Brembo stainless-steel discs w/ four-piston Brembo calipers " - r .... , .Single 230mm Brembo disc wi Brembo two-piston caliper Dry _ight . , 363 Ibs. capeclty , 5.3 gal. PrIce .. , . . , $18.530 I Moto Point 11 Brilliant Ave. Pittsburg. PA 15215 4121782-6191 F_ u.s.

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