Cycle News - Archive Issues - 2000's

eard about it and we've -but we finally get to ride s newest entry into the bigIiIr-stroke motocross wars. The RM-Z450 is Suzuki's first fourstroke motocrosser designed and built entirely on its own - no help from Kawasaki this time like with the RM-Z250 but Suzuki would be lying if it didn't borrow at least a few ideas from Honda and Yamaha, the forerunners of the new-age four-stroke motocross bike. But just eyeing the all-new RM-Z450, you can easily see a lot of Honda influence here. Most obvious: the frame. Like the Honda CRF450R, the Suzuki cradles its four-banger in a twin-spar aluminum frame, but Suzuki did borrow a lot of the technology that went into building the forged and extruded frame from itself. The method of construction was pioneered by Suzuki's road racing department, which began experimenting with aluminum frames back in the early '80s, which led to the first production aluminum-framed GSX-R street bike in 1985. So, Suzuki is by no means a novice when it comes to building aluminum frames. And, like the Honda, the Suzuki RM- 22 Z4S0 is fitted with Showa suspension components, including the 47mm twin-chamber cartridge fork; the RM-Z250, on the other hand, got Kayaba absorbers. A lot of this, however, had to do with Kayaba-Ioyal Kawasaki being in charge of the KX2S0F/RM-Z2S0's chassis department, so you don't see very many similarities between the RM-Z450 and RM-Z250 when it comes to the chassis. The RM-Z450 and RM-Z250 motors, however, do share some basic designs and layout but have obvious differences. The 450 displaces 449cc with an oversquare bore and stroke of 95.5 x 62.8mm, and the two intake and two exhaust valves, operating via chain-driven dual overhead cams, are made out of titanium instead of steel. Unlike the 250, the 450 incorporates a counterbalancer shaft, gear-driven off the magneto rotor to reduce vibration. The 450 also sports innovations such as SASS and SAVS. SASS stands for Suzuki Advanced Sump FEBRUARY 23, 2005 • CYCLE NEWS System, which allows the engine mass, especially the spinning mass of the crankshaft, to be positioned as close to the ground as possible while maintaining ground clearance, and also keeping the engine as short as possible. All this is made possible by going to a semi-dry-sump lubrication system, where the crankshaft and transmission oil chambers are kept separate. Sound familiar? SAVS stands for Suzuki Active Vent System, which, because of a one-way reed-valve in the transmission compartment, reduces unwanted pressure under- neath the descending piston, which Suzuki claims improves power output and throttle response. A lot of attention went into keeping the overall physical size of the motor as small and compact as pOSSible, which is one of the reasons Suzuki went with a four-speed transmission. Suzuki claims it was able to trim 30mm off the width of the motor by going to a four-speed gearbox and was able to save some significant weight in the process. Plus, it allowed the clutch to be positioned closer to the bike's centerline for better weight distribution and, thus, improved handling. Like most of the 450s, the RM-Z450 gets a 40mm Keihin FCR flat-slide carburetor that incorporates an accelerator pump and a throttle position sensor linked to a digital COl ignition. On the other side of the cylinder, spent gases are dispensed via a titanium headerpipe and a repackable aluminum muffler. Suzuki didn't skimp on some of the smaller stuff like it did with the RM-Z250 (although Suzuki will probably blame Kawasaki for that). Unlike the 250, the 450 gets titanium footpegs and aluminum handlebars - and thick-wall tapered Renthal handlebars at that! Although we have yet to weigh the RMZ for ourselves, when we do for our upcoming 450 shootout, we expect the Suzuki to tip the scales around 230 pounds dry. (Suzuki claims 220.)

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