Cycle News - Archive Issues - 1990's

BimotaSBBR Riding Impression 17 Michelin TXl5 (which further helps .increase front weight bias) mounted to the handsome Antera front wheel feels planted in turns, and the fat Paioli forks - whose gold stanchions denote the lowfriction titanium-nitrate coating applied to them to improve low-speed response .- ride bumps so well on the angle that you can maintain unlikely corner speeds quite. safely on 'what is, after all, a big twin. . Yet it is also a very light one by the standards of the class, with the Bimota's claimed dry weight of 387 pounds Ii whopping 46 pounds lighter than the TLlOOOR in spite of sharing the same 130-pound engine. You feel the benefits of this in the way the SB8R can be chucked around almost on autopilot. And for an extra 3 million lire, you can have the SB8R Special, available only in black, that saves another couple of pounds thanks to the use of assorted extra carbon-fiber and aircraft-alloy hardware. Bimota has avoided going overboard on rear-tire sizes, fitting the 180/55-17 Michelin TX25 fitted to a 6.0Q-in. rim to help the bike change direction easily while still putting the power to the ground, which it especially does well out of slower turns. Be prepared, however, to have the handlebars flapping in your hands as the wheel lifts when you gas it up hard. And on fast corners, well, you just pick a line and know the Bimota will hold it. There's absolutely no power 'understeer, no deflection from bumps, and loads of ground clearance - nothing drags. This bike is a lot of fun to ride hard. It stops well, too. The big brakes are Brembo's best, with loads of bite giving a huge amount of stopping power, coupled with a high degree of sensitivity. And when you trail-brake into a turn, the Bimota holds its line; even if you overdo the entry speed and have to grab a bigger handful, it doesn't sit up and understeer away, in spite of the fairly radical geometry. Totally sorted. Though the 996cc (98 x 66 rom) Vtwin Suzuki engine is otherwise completely unmodified, save for Bimota's very trick siamesed stainless-steel exhaust system, this and the MareHi EFl have resulted in a remarkable 10-percent power increase compared to the TL-R. There is a claimed 137 bhp at the rear wheel in standard form, at just 10,000 rpm, with hardly any fall-off in power over the remaining 1500 revs. And that's without fitting any of the trick race-kit parts obtainable either directly from Suzuki or Bimota's own promised aftermarket kits, which should raise output to 160 bhp or more. But back in the real world, this extra top-end performance hasn't compromised the SB8R's effectiveness as a street bike. The only thing that needs more attention is the low-rpm EFI mapping on this 50OQ-mile-old development hack, to eliminate a reluctance to settle down to the 1200-rpm idle when starting up. Otherwise, the engine is as tractable and forgiving as you expect a' V-twin to be, even on the bottom end, in spite of those massive throttle bodies. The throttle action is stiffer than on the Suzuki, probably through using a stiffer spring to counter the suction. Bllt once you've survived the slightly jerky pickup from closed)hrottle, you are rewarded with smooth, instant response from an engine that spins up notably quicker than it does in Suzuki guise. This is thanks to the single injector positioned close to the butterfly and fed with a high 6-bar fuelpump pressure. This is the same basic setup Ducati uses on its '99 factory superbike engines. And once motoring, the Bimota's TL engine has an extra kick at 7000 rpm, when the rasp from the exhaust - slightly higher-pitched than a Ducati - hardens, and the engine heads determinedly toward the rev limiter. The only glitch is a slight hesitation if you roll it on hard below 5000 revs - above that and it's instant response, but lower down each big air funnel takes a moment to clear its throat. The solution is to use the gearbox a little more enthusiastically, which is no problem, because it's Made in Japan and therefore has a clean, precise change via the carbon-fiber-rod linkage. But if you want to just lope along in traffic, the engine's quite happy ticking over at 2500 rpm in fourth gear, ready to come on strong when a gap appears - pickup is strong after the initial stutter. When you settle aboard the Bimota for the first time and thumb the starter, and that trademark engine note rumbles into life with the Sound of Thunder, you have to pinch yourself to be sure you're not about to head for the hills on a Ducati. But you aren't - and instead, what New Bimota has finally delivered to the marketplace is another kind of, yes, Italian twin that unquestionably sets a new benchmark for V-twin handling, while arguably also moving the goalposts in terms of engine pe.rformance for the street. As it starts its second quarter-eentury . of existence, Bimota's not out of the woods yet on its comeback trail- but the SE8R is such a good bike that the company must now be deemed to have a serious shot at survival. At least, along the way, it's bought Francesco Tognon and his men another round of drinks in the last-chance saloon! CII its creator • TI N .;:: CL c( 18 e SBSR was the final product designed by Pierluigi Marconi, Bimota's chief engineer for eight years, who left U1.e company just more than a year ago to head up Aprilia's new design studio based in nearby San Marino. However, even with the benefit of hindsight, it was a job well done, says its creator today. "This is the design I am more proud of creating than anything else I've ever done," says Marconi, ''because we resolved all the traditional packagl11g difficulties associated with 90degree V-twins in a way no other compan.y has yet succeeded in doing - but witllOut compromises (what, like Aprilia's 60degree engine package?! - AC). So, we overcame the problen1s of too rearward a weight distribution by rotating the engine six degrees forward compared to its Suzuki TLJOOOR installation, fitting heavy items like the battery and engine-management computer in forward locations, and especially by utilizing composite chassis technology, with an aluminum upper frame spar and lighter carbon-fiber lower one. All this helped to shift weight forward onto the front wheel, without sacrificing rigidity. Until now, only Cagiva has used this type of chassis design before, but just on its 500cc GP bike." So, though designed before the Tognon takeover, the SB8R's format neatly dovetails with Bimota's new direction in terms of bringing Grand Prix chassis technology to the street. "1 also positioned the rear suspension in a novel way," con- tinues Marconi, "not only to further increase front weight bias but also for other reaSons. Compacting the mass of the bike and placing its center as close to the center of gravity as possible has a very beneficial effect on chassis behavior, by reducing weight transfer under acceleration and braking, as well as promoting more stable handling. Originally, I placed the shock next to the rear cylinder, but this made the bike rather wide and the shock overheated. So I moved it further forward to its present position by the front cylinder, where it's actually better cooled than in its normal place behind the engine. I then operated it directly from the swingarm via a long rod, in a imilar way to the Australian Hunwick Hallam design, through a linkage which has a less progressive rising rate than my previous designs to improve traction and compliance. In fact, 1 now believe this is the onlv'correct location for the rear suspension of a V-twin motorcycle, because if you look at the bike from the side without fairing, you'll see how compacted all the mechanical parts are. And the 52/48-percent forward weight bias - SO/SO-percent with a 72-kg. rider - coupled with the short 13950un wheelbase, are benchmark features for a 90degree V-twin four-stroke, completely justifying the layout." Presumably Suzuki tried to achieve similar objectives with its innovative but widely criticized rotary rear damper. Did Marconi think of employing that on the Bimota SB8R? "Firstly, let me say that we chose the Suzuki engine because it's the finest V-twin motorcycle engine yet brdUght to market - make that a 9O-degree V-twinJ - with a good architecture, strong bottom end, great clutch, welJ-designed gearbox and above all, race-quality cylinder-head design. It has huge potential in TLlOOOR form, because if you strip the motor apart, there's not a single bad part in it. But though the rotarydamper rear-suspension design is very farsighted, and could be made to work well with some intensive development, we didn'l use it for two reasons. One is weight - it's heavier than a conventional shock, and forward Jocation would also have been difficult. But the main reason was a practical one. The SB8R was always intended as a superbike design for customers to race, and you can go into any Ohlins service van and use their accumulated knowledge to get the same settings for your shock as Carl Fogarty uses on his bike - whereas wilh the rotary damper, you're working in the dark. r know from the Tesi project what it costs to be avant-garde. The SB8R was desigred to be user-friendly, hence the Ohlins rear s)1ock and Paioli telescopic forks~' Okay, mission accomplished - but dO<.'S he have any regrets with the way the bike turned out? "Only one: The frontal area is wider than 1 wanted, or than a V-twin should really be, because of the need to fit a pair of radiators (since increased to three, in production form - AC). The engine makes too much power! I wanted to fit sidemounted radiators, like on the Honda VTRlOOO, which is a feature J really admire and would make the bike much slim-' mer. But. we needed time to study the pressure-zone technolo'l gy this requires, and there was no time, nor any budget to use a wind tunnel to help develop this. Now, here at ApriIia, we I use one all the time."

• Cover