So much for all that jibber-jabber about the Sportster-derived Thunderstorm V-twin being "the perfect powerplant" for Erik Buell's minimalist sportbikes... Buell Motorcycles celebrates its 25th anniversary in 2008, and is marking the occasion with an all-new, liquid-cooled(!) engine designed in collaboration with Austrian manufacturer BRP/Rotax, thrusting Buell firmly into the 21st century. With a claimed 146 horsepower and none of the obvious idiosyncrasies of the old air-cooled pushrod mill, it looks like Buell has built the bike that American sportbike enthusiasts have been waiting for at last.
Though it looks similar at first glance to the familiar XB12R Firebolt (which remains in production for 2008, along with most of the air-cooled XB lineup), the 1125R is in fact a fresh machine with a dedicated chassis, numerous component upgrades and, of course, the new Helicon V-twin engine. With its cylinders spread 72 degrees apart, the Helicon is not a repurposed Aprilia engine as widely speculated, but a clean-sheet design built exclusively to the American company's specifications. Displacing 1125cc, the big-bore (103mm) and short-stroke (67.5mm) configuration was engineered to maximize available valve area for better breathing and insure a proper, quick-revving character. Claimed performance figures of 146 bhp at 9800 rpm (against a 10,500-rpm redline) and 82 lb.-ft. of torque at 8000 rpm suggest initial success.
The Helicon says auf wiedersehen to pushrods in favor of a novel DOHC arrangement utilizing an independent, self-adjusting chain on each cylinder to rotate the intake cam, which in turn rotates the exhaust cam via a gear drive-a system said to save both cylinder head space and weight. Four valves per cylinder are actuated with Formula 1-inspired finger followers to insure quicker valve opening and eliminate valve float, as well as allow valve angle to be set at a steep 18 degrees so the massive 61mm throttle bodies can be mounted in a downdraft configuration.
The so-called Intuitive Response Chassis (IRC) is likewise all new and said to be the stiffest Buell frame yet. The engine is employed as a stressed member with the swingarm bolted directly to the cases. Fuel is still carried inside the main frame spars (with capacity increased from 3.8 to 5.6 gallons), but oil is no longer carried in the swingarm. Instead, it's held in an integrated reservoir in the lower left crankcase, circulated by a dry-sump lubrication system. The wheelbase is also increased to a more conventional 54.6 inches, compared to the Firebolt's 52-inch figure.
The remainder of the 1125R's design elements honor Buell's Trilogy of Technology: chassis rigidity, low unsprung weight and mass centralization. The massive muffler remains mounted beneath the engine, and an evolutionary version of Buell's Zero Torsional Load (ZTL) front brake minimizes unsprung weight up front. Inspired by the prototype version on last year's XBRR racebike, the new eight-piston caliper features a massive housing optimized for clamping stiffness and heat dissipation. All-new bodywork is likewise inspired by the XBRR, featuring a broad upper fairing designed with the aid of computational fluid dynamics (CFD) to optimize aerodynamics and enhance rider comfort in what the acronym-mad marketeers in East Troy are calling the "Quiet Zone" cockpit. CFD was likewise utilized to sculpt the massive cowlings that direct cooling air over the twin longitudinally mounted radiators (and into the ram-air intake system), as well as move hot air away from the rider.
Everything else about the 1125R is cutting-edge sportbike technology. The six-speed gearbox is navigated with assistance from a hydraulically actuated clutch with a hydraulic vacuum-assist slipper mechanism to ease corner entries. The new Showa 47mm inverted fork is fully adjustable, as is the shock. The foot levers are adjustable. The cockpit features an onboard diagnostic information system that includes lap time and split functionality. No detail was overlooked to make this new Buell one of the most advanced and innovative sportbikes on the market.
We liked the XB-series Buells well enough, but always with caveats-an anachronistic engine character that seemed utterly out of step with the innovative chassis design tempered our admiration. Now it appears that Buell, with help from Rotax, has presented us with an updated powerplant that is every bit as modern and as intelligently designed as the chassis that conveys it, creating what is clearly the most significant and important bike in the company's history. Happy silver anniversary, then, and here's to what we hope will be the culmination of Erik Buell's effort to create a truly "world-class" American motorcycle. We can't wait for our First Ride next month!
Engine type: l-c 72-degree V-twin
Valve train: DOHC, 8v
Bore x stroke: 103.0 x 67.5mm
Clutch: Wet, multi-plate slipper
Claimed horsepower: 146 bhp @ 9800 rpm
Claimed torque: 82 lb.-ft. @ 8000 rpm
Frame: Aluminum twin-spar with aluminum swingarm
Front suspension: Showa 47mm inverted fork with adjustable spring preload, compression and rebound damping
Rear suspension: Single Showa shock with adjustable spring preload, compression and rebound damping
Front brake: Single ZTL eight-piston caliper, 375mm disc
Rear brake: Single two-piston caliper, 240mm disc
Seat height: 30.5 in.
Wheelbase: 54.6 in.
Fuel capacity: 5.6 gal.
Claimed dry weight: 375 lbs.