Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/127776
to justify its increased cost - especially as the YB9SRI doesn't have the same all-ornothing power delivery as the previous four-cylind er homologation special fitted with TDD/Bimota fuel injection, the flawed Suzuki-engined SB7. The YB9SRI's twin-spar chassis made from anticordal aircraft alloy h as the same basic design as the previous bike 's, but now has a cast rear fram e brace in front of the back wheel, to which the similarly cast rear upright incorporating 'th e s w i ng a rm pivot is welded . Th is makes for an even more rigid structure to cope with the extra grip d elivered by new-generation super sp ort race tires, which ever mo re closely resembl e slicks with a nominal tr ead pattern molded into th em. Those fitted to th e s treet YB9SRI as sta nd ar d ar e Michelin Hi Sports - though Fast Fred (Bayens ) will us e Pirellis for Thunderbike racing mounted on new, very distinctive castaluminum wheel s made to Bim ota ' s design by Antera, the first motorcycl e d esi gn by the sa me compan y which manufactures th e w heels used on Ferr ari and Pors che s por ts cars. Th ese weigh exactly the same as the Marchesinis used by Bimota before, but the rear is actu ally bigger, at 5.50 in che s w ide in stead of the 5-incher used on the carburet ed YB9. Th e swin garm has be en wid en ed slig htly t o acco m mo d ate th e wider wheel. This new width allows Bimota to fit a fat 180 /55ZR17 rea r tir e in st ead of a 160/55. Th e front tire is a 120/ 70 front on a 3.50-inch wheel, as before , Wn at was that about junior supe rbikes? Though chassis geometry is other- , wi se unchanged , th e 55.5-in ch wheel, base and 24-degree head ang le with just 95mrn of trail make the YB9SRI feel even m ore like a four-st roke 250cc GP bike than before. The reason is a combination of the rear ride-height setting on th e bik e as I rod e it, and the close-cou pled riding position , with th e na rrow, di stinctiv ely styled bodywork (now with a three-way split for improved access in the race paddock) and its trad emark Vneck Bimota screen . ' The test bike had just returned from th e Magione circuit, where the factory development team had set it up for optimum race -track handling, with a 7mm lon ger rear shock setting. Th is se tting translates into substantially increased rear ride height compared to a machine set up -for street use . For the tra ck, the h igh se tting allows adequate ground ' clearance at racing speeds with the extra grip from the fatter rear tire (especially fo r the freer-flowing Bimota exhaust which contribu tes to th e 6-p e r ce n t power increase), bu t at the cost of making the chain rub hard on the swingarm o n overru n, p ro d u cing an irritating (Above) Handli ng .on the YB9SRI is more li ke a 250cc GP bike than 600cc supersport. (Right) The control unit for the fu el Injecti on is mounted under the seat . Thi s system, along wit h a spec ial exhaust , raises output from .th e 600cc Yamaha powerplant to 106 horsepower. (Below) Four 44mm throttle bodies feed the 62 x 49.6mm cy linders for outstand ing eng ine response. noise as well as p resu m ably undue wear. The jacked-up rear en d also delivers a radical rid in g position th at is more 250GP than Supersport 600, with a lot of your bo dy weight on your arms and shoulders, thanks to the low-set clip-ons which are also quite steeply raked. This makes the YB9SRI as tiring to ride for ·any length of time on the street as Max Biaggi 's world champion 250cc Aprilia is on the track, making each 150-mile tankful from the 5.3-gallon fuel tank a ph ysical challenge of endu rance. A twohour stin t of coping with sw it ch back mountain road s left me with sore wrists. This soreness was exacerba ted by the ou ts tand ing braking delivered by the Bim ota' s 320mm Brembo fr on t di scs, ano the r powerful weapon in th e bike's armory for Superspo rt racing. Though more cost-effective steel rotors are used in this application, rather than the more expensive cast-iron discs use d on Brembo-equip ped su perbikes, these are a big improvement over similar budget Brembos I've used recently. They offer noticeably improved bite, matched with lots of sensitivity that allows you to stroke off a bit of excess speed with light pr essure on the lev er, or altern ately to squeez e hard and get the back wheel waving in th e air - and it 'd oes, thanks to th e increased front-end weight bias wi th the higher rear ride height setting. Set up as it was for track use (the suspen sion linkage is fully adjustable, so you can tailor the bike to suit individua l taste), the Bimota' s steering was flaw less. You ' v e ju st got to think abou t changing direction, an d the bike does it - yet without bei ng twitchy or overly-