Suzuki's DR-Z400SM supermoto bike is a hoot, no boubt adout it. Lightweight, slim, highly maneuverable and blessed with long-travel suspension, it makes even the daily commute a blast. Traffic snarled up? Duck down that side street, hop over the curb, cut through the back alley and pop out a block over, where traffic is flowing. Blacktop, dirt or any surface in between, no problem.
The 324-pound (wet) DR-Z is a great entry-level bike, too, especially for someone coming from the dirt side of things. Its 35-inch seat height sounds daunting, but the suspension sags a few inches under the rider's weight, so it's effectively lower. Of course, that soft suspension can be a handicap if you flog it at the local supermoto/kart track like we did. And no matter where you ride it, the 398cc single makes a paltry 35.6 horsepower and 26.2 pound-feet of torque at the rear wheel, which is a polite way of saying it's s-l-o-w. During drag-strip testing for our street-legal supermoto comparison ("Swinging Singles," Motorcyclist, July 2006), the DR-Z suffered that most humbling of specifications: an "na" in the 0-100-mph category.
Fortunately, it doesn't take much to make the yellow (or black) Suzuki a better-performing motorcycle. The SM may only have hit the market in 2005, but it's based on the dual-sport S-model that debuted in 2000, so there's a wealth of tuning knowledge. Kevin Schwantz even won national-level supermoto races on one. Granted, his factory-backed bike was modified to the tune of tens of thousands of dollars, whereas we hoped to spend just $1500 upgrading ours.
When it comes to tapping into the collective conscious, there's no better place than the Internet. And when it comes to four-stroke dirtbikes, there's no better site than www.thumpertalk.com. There we found near-universal approval of the Dynojet Stage 2 kit ($64.89 from www.dynojet.com) along with a 3x3-inch hole cut in the top of the airbox. Since we planned to run an aftermarket exhaust, we set up the stock Mikuni 36mm CV carb with the richer #155 main jet, the Dynojet needle with the clip in the second position and the fuel mixture screw 3.5 turns out. In this era of electronic fuel-injection, installing the jet kit was fun-therapeutic even-or at least it was once we managed to remove the recalcitrant Phillips-head screws securing the float bowl. Do yourself a favor and replace them with Allen bolts.
Being street guys, there was only one place to go for a pipe: Yoshimura R&D. Aiming to keep things affordable, we opted for the RS3 Comp-Series slip-on in stainless steel ($375 from www.yoshimura-rd.com). Installation was a snap, and subsequent dyno runs showed 2 additional horsepower and 2 more lbs.-ft. of torque. That doesn't sound like much, but it represents gains of 5-10 percent! More impressive was the spread, with peak torque arriving 200 rpm lower at 5900 and peak power arriving 600 rpm higher at 8100. Moreover, the formerly lean engine now warmed up quicker, throttle response was snappier and the bike didn't feel between gears as often. The slip-on also shaved off a few pounds compared to the stock muffler and gave the exhaust note a nice-albeit too loud-bark. Should you want to be neighborly, order a TEC (Tunable End Cap) kit.
With the motor now running stronger, we turned our attention to the chassis. The SM is already beefed-up from S-spec with an aluminum swingarm, fully adjustable shock and the stiffer inverted fork from an RM250 motocrosser. Yet even so, its spring rates are too soft for aggressive use. So we took our suspension to Race Tech, where technicians installed Gold Valves front and rear plus a set of stiffer .46-kg-mm fork springs and a 5.7-kg-mm shock spring. Total cost: $799.41. The difference was remarkable, as the bike sagged a lot less with the rider in the saddle and snapped up into stoppies instead of bottoming under braking. Damping control was also much better, which we appreciated while backing it into corners or negotiating dirt whoops.
To keep the DR-Z's price at an affordable $6199, Suzuki cut a few corners and spec'ed a few el cheapo parts. Most notable is the steel handlebar, which is sure to bend the first time you drop the bike. Surprisingly, the '07 SM comes with an oversized aluminum Renthal Fatbar at no extra cost, so upgrading the handlebar is as easy as ordering parts from your dealer. To complete the conversion, you'll need the '07 bar, bar ends, upper and lower clamps, the nuts and bolts to hold them together and a key switch. (You really only need the key switch mounting bracket, but it isn't sold separately.) Total price for the above is a whopping $430.23, but you can't beat OE quality.
The other new '07 parts worth retrofitting are the axle sliders. These prevent damage not only to the axles and axle nuts, but also to the fork legs and swingarm-not to mention the asphalt, which is a bone of contention with some kart-track owners. Because the right rear slider gets in the way of the axle nut's cotter pin, you'll also need the '07 locknut. Installation takes maybe a minute per and total cost is $83.50. Alternatively, you could purchase aftermarket sliders designed to retain the cotter pin from companies such as Rhino (www.rhinomoto.com).
One other cost-saving omission we noted in our comparison was handguards, which protect not only your fingers but also your levers in close quarters (i.e. while lane-splitting or riding at the supermoto track). The Dirt Rider guys had a set of yellow Cycra M2 Spine Handguards lying around the office ($44.95 from www.cycraracing.com), so on they went. These worked fine for general riding, but didn't offer the crash protection we would have liked. A better bet would have been the $109.95 Probend Billet Handguards or $129.95 Probend Racer Kit.
The last parts we ordered before pausing to add up what we'd spent were Galfer brake lines and pads ($191.87 from www.galferusa.com), which made doing the aforementioned brake slides and stoppies that much easier. That brought our total expenditure to $1989.85, which meant we'd blown our budget, but it was all money well spent.
If we had to do it again, we'd have saved a hundred or so bucks by buying the Renthal Fatbar from the aftermarket instead of from Suzuki, or triple that amount by substituting a set of Renthal's new 71/48-inch aluminum bars, which would have worked with the stock clamps. The money we saved would have gone a long way toward purchasing guards to protect the DR-Z's fragile engine covers (deburring the back of the shift lever is a good start) and radiators. We also might have poked around on eBay and bought a footpeg-eliminator kit that lets the midpipe mount to the frame instead of the right-side passenger-peg bracket. A set of supermoto race tires also would have been a natural. And if money were no object, a slipper clutch. But if we were going to get that serious, we'd probably pop for a proper super-moto racebike.
Back in the real world, with our pockets picked clean, we turned our attention to those things we could improve by expending nothing more than elbow grease. Unbolting the vibration-damping rubber inserts from the motocross-style footpegs gave us better footing. Stripping the seat of its passenger grab strap let us slide fore and aft unencumbered. Trimming the rear fender and bolting the license plate directly to it made for a cleaner- looking rear end, as did removing the stock tool bag and ditching the charcoal canister and associated plumbing (our bike was a California model). And last but not least, we stripped off the reflectors and warning labels. We know we should wear a helmet and use unleaded gas, so don't need to be reminded on a daily basis.
Our low-buck DR-Z project turned out so well that after snapping photos of Online Editor Angie Loy riding it for this story, Kevin Wing took the bike for a ride...and promptly worked a deal to buy it. He took delivery just before Christmas, and later sent us an e-mail: "I hit three malls for some last-minute shopping and turned an absolute nightmare traffic situation into a riot! I was still on a high the next day and put about 120 miles on it in the Santa Monica Mountains."
Looks like it found a good home.