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/127289
New bikes,~n..=:....:....ew:. . . . . :=t.l :·re:.=. . -s _ hat's a new bike without new tires? With this thinking in mind, Dunlop has in troduced a new radial tire designed specifically for u se on Suzuki's 1991 GSXR 750 and 1100. Dubbed the D202, the front tire (120170ZR 17) uses current radial tire technology and employs two Kevlar belts laid on top (at an angle of somewhere between 16 and 18 degrees) of a true go-degree radial two-ply carcass. . The tread pattern on the front features more grooves to give the tire more co m p liance and neutral steering characteristics. The rear tire (170/ 60ZR I7), which was developed in Japan, features an all-new construction design (Jointless Belt) where th e two angled Kevlar belts are replaced by a single Kevlar cord that is wrapped around the circu mferen ce of the tir e in o ne con tin uo us piece. T he lower sidewall design still incorporates-an apex piece to stop th e tire flexing o n the rim flan ge. T he O-degree J ointless Belt (J L B) design keep s cen tri fugal gro wth dow n, . thus keeping the tread shape cons tant, acco rding to Dunlop spokesman Tony Mill s. The tread design follows the curre nt trend of less gr ooves, more slick area. Dunlop's goal with therear tread pattern was to provide dr y stab il ity, whi le not forfeiting any wet traction. Wh ile there are fewer grooves, they are wider than normal. The Dunlop/GSXR rela tionship goes back to th e original 1986 GSXR which featured Dunlop K700s. Last year , however, the GSXRs came fi tted with Michelin tires. " We've tuned th ese tires to this motor cycle," Mill s said. W righ t direction even whe n you need it most - on the bu mpiest of corner exits . Rear suspe nsion o n bo th bikes is u nc ha nged. T he 750 features a singleshock, link-type. Showa that featu res fu lly-a djustable spring pre-load with four rebound and 12 com p ression da m ping settings. T he 1100's Kayaba uni t is of simi lar design. Even a quick glance at the new GS XRs reveal s th eir n ew fairi ng des igns. T he more-po inted nosepiece so mewha t resembles tha t of Suzuki's RGV500 GP bike, and produces a reduced coefficient of drag (do wn 2.3% o n the 750 and 3.5% o n th e 1100). In addition to its more-pointed design, th e windscreen has also been lowered. Other cosmetic changes incl ude less bulge on the tail pi ece; a slightly wid er , rear seat ; a recessed headlight and th e _addition of a runni ng ligh t; twin lenses on the tailight; and slightly different , fro n t fender mounts. The riding position and co n trols are . " unch an ged for '9 1, still offering go-fast riders the optimum riding position while po ssibl y proving uncomfortable for long-distance touring. Both bikes feat ure adequate ground clearance and J fairi ng grounding shoul d be a th ing of the past for the majori ty of street -riders. The 750 is still easier to ride than " the 1I00, allowing the ride r to make . tran sitions wit h less effort and thus quicker. But the 750 can' t match the awesome po wer outpu t of its big sister, \'and Ro ad Atlan ta 's back straight was nothing more than a blur on the 1100. , T he pair co me fi tte d with n ew Dunlop D202 Sport Radial s (se e si de ba r), and still fea ture 17-inch wheels at both ends. Turning to the GSXR's respective powerplants we find . more ' changes, albeit so slight. The mos t significant change comes to the valve train. A new valve train sees each valve operated by an indi vidual ca m lo be and a single rock er arm; and valve lash is adj usted by a shim located at the top of each valve • spring retainer. T he val ve train has been changed primarily to reduce inertial ma ss an d mechanical loss. In addi tion, the 750 now uses higher rate GSXRI100 springs to reduce valve float at high rpm. The valve stems and g ui des have also been lengthened, although the valve sizes the msel ves remain the same. The 750 has also undergone a valve' ti ming change, with the in tak e timing goi ng to an earlier time of 63° at bottom dead center from last year's 700. Valve adj us tments are now sim p ler, according to Suzuki, with no valv edepressing tool required. Suzuki recommends valve adjustments at 3500-mile intervals. The 750's cylinder head has been recasted fo r 1991 with' the intake and exhaust ports reshaped 'to improve flow and cylinder charging. The center rib dividing each port has been moved back and features a more tapered edge. Additional machining . on th e valve seats ha s smooth ed ou t th e port to improve fuel flow . The 1100's changes are in th e in tak e o nly and not in the exha us t port. Suzuki spokesmen claim no peak horsepower gai ns, bu t say th ey were concerned primarily with power applica tio n ~ get ting the power to the gr ound. Thus, the power is designed not to fall off as quickly. For emis sion reas ons, the II 00 will use 36mm Mikuni carburetors rather th an the 40m m units used in th e rest of th e world. Like last year's model, the 750 will use 38mm Mikunis wi th the exception of California which gets 36mm carbs thanks to its mor e stringent emission regulatio ns. The 1100's five-speed transmission has been stren gthen ed by using a do uble-ro w ball bearing o n th e countershaft, T he 750's six-speed gearbox is unchanged for '91. The new G SXR7 50 is avai lable in blue/white and black / silver (p urple accent, most not abl e wh eels) color com binatio ns while the 1100 comes in simi liar blue/white livery in additio n to its red/black color sch eme. The 750 carries a suggested retail price of $6499 wit h the 1I00 -sel ling for $7299. QI 1IOCl<11l ................,. 00 Rt? 8 \ 0 8 0 8 1<) I eoo (Above) The new valve train ' on the GSXR sees each valve operated by an individual cam lobe and a single rocker arm. (Below) The GSXR750 at' home on R oa d Atlanta's 2.5-inile road course.