Weird Science

Say you're the head of design for a motorcycle company with what seems like a pretty simple assignment: Build a midsized, go-anywhere, do-anything streetbike for the American market. Make it respectably quick, reasonably comfortable and rationally priced. It has to work on the street, on the test track and in your prospective customers' neural pleasure centers. It's not enough to be right in some sterile, objective sense. It has to feel right.

You're looking at two very different answers to that question: the new Buell XB9SX Lightning CityX (that's City Cross, according to Erik Buell) and Kawasaki's new Z750S. You might guess the Buell, priced $1596 more than the $7099 Kawasaki, would start out with a distinct emotional advantage. It is the latest brainchild of one relentlessly innovative genius, aka Erik Buell. It's definitely not the latest in a long series of conventional Japanese streetbikes.

Both fall into the midsize, upright, naked-bike category, with a few exceptions. Kawasaki's Z750S four wears a fairing oriented more toward practical wind protection than racing pretense. And the Buell's urban brawler pushes the upper limits of middle displacement with its 984cc Milwaukee-derived pushrod V-twin. Still, both bikes are variations on the same real-world streetbike theme.

Underneath its angular bodywork and edgy styling cues, the Z--the milder-mannered brother of the belligerent Z1000--is a blindingly logical example of the Universal Japanese Motorcycle, designed to do almost anything a street motorcycle should. Intended primarily for Europe, where people actually buy motorcycles for pragmatic reasons, the 750S has gained practicality with a bigger, more useful fairing--and lost a bit of horsepower via a sleeved-down, 748cc version of the Z1000's inline-four. The 750S's frame uses large-diameter steel tubing, with bolt-on plastic panels to impersonate a racier twin-spar aluminum skeleton.

You sit essentially upright in the roomier Z750S cockpit (left), while CityX accommodations define compactness. Instrumentation is excellent on the Buell, and a tough plastic pad keeps your tank bag from scuffing the faux fuel tank.

The 750S employs various cost-cutting tricks to hit its $7099 price point. The 41mm fork is non-adjustable. Blue-collar dual-piston calipers grab 300mm front rotors, and a single 4-into-1-exhaust replaces the Z1000's pickle-fork system. Ancillary bits are a parts-bin smorgasbord, with the taillight and the instruments lifted from the ZX-10R.

The CityX is an entirely different species. Where the Kawi asks, "What would you like?" the Buell demands, "What are ya lookin' at?"

There's nothing universal or conventional about a cast-aluminum frame that doubles as a fuel tank, or a swingarm that doubles as an oil tank, or a single front brake that uses a ring bolted to the rim.

The CityX uses the 984cc version of the Sportster-derived Buell engine: oversquare cylinders are fed by a 45mm downdraft throttle body and cooled with help from an electric fan. The 45-degree V-twin's Uniplanar engine mounts allow it to shake, rattle and roll vertically without disturbing the chassis or rider. Drive is via toothed belt held in constant tension by a fixed aluminum roller. The muffler? It's strapped under the engine like a bomb to the belly of a Hellcat fighter, saving room and centralizing mass.

To compensate for that tall, heavy twin and high-inertia crankshaft, the Buell's ultra-short chassis uses ultra-steep steering geometry. In this, as in just about every other area of motorcycle design, Mr. Buell does it his way, or he doesn't do it. The aluminum-intensive fuel-carrying frame is common to all late-model Buells. For devotees of casting artistry, it's simply delicious.

The inverted fork and shock are from Showa, and both are fully adjustable. The zero torsional load front brake bolts a single rotor to the rim, not the hub, shortening the path of braking forces on their way to the tire. This allows for a lighter wheel, and the large-diameter rotor also provides added leverage compared with a conventional disc, eliminating the need for a second.

In the city, where the Buell was designed to live and where the Kawasaki will likely spend much of its time as well, the two machines get to the same place via different routes.

Like most basic Japanese motorcycles, the Z750S is exceedingly straightforward. The riding stance is upright and roomy save for high, forward-mounted pegs that put kinks in long legs. The firm seat slopes forward, sliding you into the tank on long rides. The engine likes to spin. It's tractable at low revs, if not particularly strong.

The four gets a bit buzzy at 6000 rpm, blurring the mirrors and tingling the rider's contact points. Real power kicks in at 7000 rpm, building to a 101-horse peak at 10,750 rpm. With its wide bar and sit-up stance, the Z750S is amazingly agile in traffic.

Rapid forward progress is a momentum game on the CityX. Although it never feels as agile as its chassis numbers might suggest, a commendably stiff frame, compliant suspension, grippy Pirelli rubber and acres of cornering clearance let you carry big speed when the road turns twisty. High footpegs allow lurid lean angles without touching down.

The Buell is an entirely different animal. The seat is tall, soft and rounded, and you're perched so high and forward you feel like you're wearing the front axle as a goatee. The engine rips away from a green light in its lazy Harley staccato while the muffler funnels exhaust onto your left boot. Buell's engine mounts are brilliant, completely isolating the rider from vibration anywhere above idle.

The CityX engine's flywheels are heavy, but the 45mm throttle body, tuned for high-end power, makes the engine lethargic off-idle. A rapid departure requires revs--and keeping your throttle hand a half-second ahead of the engine. There's less power below 4500 rpm than you'd expect from a 984cc V-twin.

From 4500 to the 7500-rpm soft rev-limiter, the power is satisfying, with a peak of 74 hp at 7250 rpm. But redline comes up fast, and when it comes you need to shift. The transmission itself works quite well, and the clutch is reasonably smooth. But those heavy flywheels and lethargic throttle response complicate every quick trip through the gears. Even if you're in a hurry, the CityX isn't. It's possible to be smooth, and it's possible to be fast. But it's very hard to be both at the same time.

The short wheelbase and steep steering do their part to quicken the chassis' initial reflexes, but as you lean the CityX you become progressively aware of the large lump of whirling steel and aluminum directly under your larynx that's slowing roll response. In the city, where there's more cutting and thrusting than leaning and carving, the chassis works very well. The tall seat, high pegs and close-couple riding stance feel weird at first, but that wears off quickly. Suspension action is smooth and compliant, even over nasty pavement. The single front brake is more powerful than the Z750S's pair, and gratifyingly linear as well.

On the highway the Z750S has the Buell covered. Its fairing shields your torso from the blast with zero helmet buffeting. In top gear the engine is below its 6000-rpm buzz at 75 mph. Your butt, hands and feet are calm, but the mirrors aren't--they might as well be labeled, "Objects in mirror not as numerous as they appear."

The Buell is perfectly ridable for long distances as long as you like wind. The wide bar lets you impersonate a kite at freeway speeds, and taller riders will need more legroom. Otherwise, you're fine for 150 miles or so between fuel stops. Highway traveling reveals another surprise: Cruising at 70 mph in top gear, the engine is so far below its power zone it takes a downshift to accelerate hard. The Kawasaki will leave it for dead in a 60-80-mph top-gear roll-on.

In the hills, the differences between the two machines are more obvious. Recent Buells are notorious for standing up and running wide if you brake mid-corner or shut the throttle suddenly, but the CityX is much better behaved than previous examples. Credit the more rounded profile of Pirelli's Scorpion Sync radials for some of that. Initial steering effort is light, but it takes a surprisingly hefty shove on the bars to lever the bike to full lean or quickly change trajectory.

Still, the unique chassis does its part. The suspension works well. The steering geometry is strange but workable. The brakes are plenty powerful, the tires are top-notch and cornering clearance is abundant. Still, that great hulking engine keeps the CityX from being a truly cooperative back-road weapon. A shortage of usable power below 4500 revs encourages higher revs, but leisurely throttle response and immense rotating inertia make smooth, sporty downshifts harder than upshifting.

Things calm down in the lower half of the rev band. But power production is limited there, and speed drops accordingly. We know Buell has moved mountains coaxing top-end power from what is essentially a low- to-midrange-oriented engine. We also know flashy peak power numbers sell motorcycles. But the X would be much easier to ride and faster over a given stretch of twisty road with a little less top-end punch and more in the midzone.

Meanwhile, when the Buell's engine signs off at 7500 rpm, the Kawasaki's is just getting started. Its longer chassis and orthodox riding position encourage aggressive cornering. The quality and quantity of horsepower make it easy to leave all but the most determined Buell riders behind. The steering geometry is slower on paper, but the Z's high, wide bar and relatively low center of mass let you sit there and steer. The dual front discs require more effort than the latest supersport bits, and the lever is too skinny for comfort, but you get used to it.

The Buell's overachieving 984cc pushrod twin makes more torque than the 750's 748cc four. Despite a torque peak that arrivese 2000 rpm earlier, the CityX wants to sping against the engine's 7250-rec horsepower peak to generate real thrust. The Kawasaki shrieks all the way to an impressive 101-horse peak.

The Kawasaki's cheap suspension bits are not as precise or compliant as the Buell's, but the more cooperative chassis lets you work 'em harder right out of the box. Fast, bumpy corners unsettle the chassis, but if you're going that fast proceed immediately to the Ninja department. Cornering clearance is fine for mortals on smooth roads, but a big rider in a bad mood will drag various hard parts.

So? Picking between these machines--or one of the other nude motorcycles they compete with--is as much about you as it is about them. Do you want a motorcycle that works very well in just about any riding situation but doesn't make much of a statement? Or do you want a brash, wildly styled technological master's thesis?

The good news is there's no wrong answer here. It's about riding, not racing, we say. And if it feels good, ride it.

Dyno Chat
The Buell's overachieving 984cc pushrod twin makes more torque than the 750's 748cc four. Despite a torque peak that arrives 2000 rpm earlier, the CityX wants to spin against the engine's 7250-rev horsepower peak to generate real thrust. The Kawasaki shrieks all the way to an impressive 101-horse peak.

Ergos
Stuffing a 984cc V-twin into very little real estate doesn't leave much room for tall riders, but the CityX is surprisingly accommodating--unless you're an NBA center. Wider bars make urban maneuvering easy. The Z750 can't match the Buell's brass-knuckles attitude, but the Kawasaki's more orthodox ergonomic arrangement is more comfortable for a broader range of riders, especially on longer rides.