Suzuki DR-Z 400SM

Engine

Road Test

The Japanese Big Four have toed the rising supermoto tide, offered limited support to a few racers, but not yet truly taken the plunge.

Well, Suzuki is in above its waist for 2005, becoming the first of the Four to include a production supermoto bike in their North American model line. While hardcore racers may be more interested in Suzuki's new RM-Z450 four-stroke motocrosser as the basis for a supermoto conversion, the new DR-Z400SM is a turnkey street-legal supermoto that's both refined and affordable. It's also an absolute hoot to huck around city streets and tighter backroads.

Taking a straightforward approach, Suzuki used its tried-and-true DR-Z400S dual-purpose bike as the stepping-off point for the new machine. The DR-Z's motard makeover includes all the basics—shortened front fender, upgraded front brake and wide 17-inch wheels fitted with grippy sport tires. Suzuki could've pulled a stoppie right there and proclaimed things good to go, but chose to take the conversion to the next level. The S-model's conventional fork was upgraded to a fully adjustable Showa 47mm inverted unit and its swingarm is an attractive tapered-aluminum item—both pieces derived from the RM250 motocrosser.

Aside from using a racing-type supermoto muffler, the only tuning change made to the S's 398cc, liquid-cooled, dohc, four-valve Single is slightly altered CDI mapping to match the SM's taller final gearing. The SM also shares the S's 36mm Mikuni CV-type carburetor and 11.3:1 compression ratio (to allow use of 87-octane fuel), while the off-road-only models gain a bit of power due to their flat-slide carb and higher compression ratio. With this engine entering its sixth year of service, there's no shortage of aftermarket performance parts that can be readily applied to the 400SM.

The convenience of electric-start not only makes life easy on your right leg, but also eliminates any worry of stalling the motor at a stoplight and holding up traffic while frantically kicking through a tedious hot-start routine. The keyed ignition switch is located atop the triple-clamp and a pull-choke knob resides down on the carburetor. An automatic decompression system allows the engine to crank over freely, and cold starts were a snap, requiring only brief use of the choke before being able to ride away without any carburetion woes.

First gear is fairly short, working in concert with the light and fluid clutch action to provide super-easy launches. Operation of throttle and brake also has an exceptionally feathery feel. Our testbike's shift action was slightly notchy, but it should be noted the bike arrived with less than 100 miles on the clock and has shown improved shifting feel as the miles mount.

Gearing is well-suited to city riding, where zipping from light-to-light sees you working to the top of the five-speed gearbox within a block. Running at 50 mph in high gear is where the SM's sweet spot is found. At this speed, very little engine vibration is felt through the handgrips and fuel tank. Speed up a bit and the bars develop a mild buzz, while the tank and seat are dead calm. Go faster yet and the buzz leaves the bar and heads south through the chassis, but relative to most four-stroke Singles, the DR-Z mill is incredibly smooth at any speed.

Even on the freeway, where keeping pace in the fast lane has you revving the snot out of the motor, vibration through the bars was practically nonexistent. The handlebar is equipped with GSX-R style end weights; removing these to mount a set of supermoto-style handguards will likely sacrifice some level of comfort.

On the freeway, another cog would come in handy, as the engine sounds rather busy at speeds in excess of 65 mph. Dropping a couple of teeth off the rear sprocket to raise the gearing may be something to consider, certainly if you do a lot of highway riding. Going with a larger countershaft sprocket isn't an option, however, as doing so would cause the drive chain to contact the engine case.

Source Cycle World