Good Vibrations

Harley-Davidson engineer Brian Ruffert led a team that redesigned Harley-Davidson's legendary Sportster motorcycle, taming the vibration and boosting the quality without changing its signature look.

By Design News Staff -- Design News, February 22, 2004

Milwaukee, WI — Milwaukee, WI—Brian Ruffert was standing under the hot sun on a test track during 1998 in Uvalde, Texas, when his Eureka moment struck. There, in front of him, he glimpsed the future of Harley-Davidson, Inc., in the form of a group of executives who were struggling to shift the gears on a test motorcycle. Repeatedly, the executive riders tried and failed. Each time they tried, the motorcycle's engine zoomed past its normal shift point and roared up to its "rev limiter" at 6,000 rpm before cutting out, leaving the executives flustered. Ruffert watched this occur not once, but several times, before realizing what was happening: The executives couldn't shift the bike because its ride was too smooth. Repeatedly, they waited for the bike's familiar biomechanical signals—the quivering of the handlebars, vibrating of the seat, shaking of the foot pegs—but the signals never came. So by the time they tried to shift, it was too late.

"We had reduced the vibration so drastically that everyone was confused," Ruffert recalls.

Everyone, that is, except for Ruffert and the engineering team that had designed the test bike for the so-called "jury ride." In their minds, the dramatic reduction in vibration was the necessary tonic for the company's Sportster, the oldest and one of the most respected motorcycle model lines in the business.

Today, Ruffert knows that his instincts at the 1998 test ride were on target. Last fall, the American motorcycling giant rolled out a new Sportster, largely based on the lessons learned in the Uvalde test rides. The new bike is a dramatically redesigned, critically received, high-quality, smooth-riding update of its predecessor, yet looks not an iota different than earlier models.

"We changed everything without changing a thing," says Bill Davidson, director of marketing in motorcycle planning for Harley-Davidson, and a great grandson of founder, William A. Davidson.

Groundswell Movement

The company has a corporate quality focus that had verged on obsession since the company's lean years in the late 1970s. Back then, an ownership switch had resulted in bikes that literally had parts falling off, and company veterans of the era hadn't forgotten the lessons that emerged from those experiences.

Form and Function

Ruffert, who headed the redesign, launched the effort by incorporating what engineers had already learned in the Uvalde jury ride: that the key to reducing vibration lies in isolating the engine from the chassis. For the Sportster, however, that was a big step. Since it had entered the market in 1957, the Sportster had always been a rigid mount design; that is, the chassis and engine were always rigidly connected, which provided a big boost to the bike's structural integrity, particularly with respect to lateral torsional forces.

To maintain the balance between function and style, Ruffert and the engineering team employed rubber engine mounts about the size of hockey pucks at the crank case and be-tween the bike's frame and crank case casting. The rubber mounts isolated the engine from the frame and dramatically reduced transmission of vibration.

At the same time, the team used a triangulated, direct rigid link between the crankcase and frame. Known as tie links, the dog-bone-shaped devices provided lateral rigidity, thus preventing the engine from wagging from side to side, but allowing it to move in the fore-and-aft plane.

The key to selection of the mounts was their performance on test frames, engineers say. They selected natural rubber mounts measuring 1.7 inches thick in what they called a "rubber sandwich" configuration where each mount is sandwiched between steel plates. Front mounts are 2.75 inches in diameter, while rear mounts measure about 3 inches.

Engineers placed the puck-shaped mounts at the front and back of the engine's crank-case, between the crankcase and the motorcycle's frame. They then moored the tie links at three spots: one low on the engine; another higher, near the cylinder heads; and a third at the back, near the rubber mounts.

Placing the tie links and rubber mounts in those locations, however, was no easy task. The decision was preceded by months of physical testing on frames and linkages, and was accompanied by numerous finite element analyses of the engine and frame using UGS PLM Solutions' I-DEAS Master Series software.

Customer Input

Once the frame group had selected locations for mounts and tie-links, powertrain engineers jumped on board. From then on, a mountain of design changes cascaded down from the initial frame alterations.

One was the development of a crankcase onto which the rubber mounts could be easily integrated. The engineering team collaborated with the company's manufacturing group on the machining of the castings. They teamed with a crankcase castings supplier to perfect the castings, and then met with the assembly team to make sure that every part could be hung on the transfer line while still offering simple assembly.

Engineers also incorporated such changes as improved seating, as well as re-positioned hand grips and foot pegs. They also reduced the hand grip diameter from 1.25 inches to 1.125 inches, which the company says appeals to smaller riders while being unnoticeable to larger ones. Similarly, they went to a new brake manufacturer to reduce the lever effort required for the front brake, and changed the gearing of the motorcycle to diminish the spring rates of the clutch spring pack.

Enthusiast Culture

While the prospect of such never-ending customer input may conjure up visions of chaos for experienced engineers, it's an unsurprising approach for those who know Harley-Davidson. In its current-day culture, Harley is run by motorcycle enthusiasts from the top, down. Its executives, including those who struggled with the test bike in the Uvalde jury ride, own their own bikes.

When the company unveiled the new Sportsters last summer in conjunction with Harley-Davidson's 100th anniversary, that passion was evident, engineers say. Dealers who took a sneak peak of the new machine and rode it on dynamometers in Las Vegas last July were said to be in awe of the smoothness, even as they raced it up to 100 mph. Similarly, the new bike drew applause from reviewers, including Cycle World, which said that Harley-Davidson has "given us a new Sportster, an improved Sportster, and it's still, as it has been since 1957, a Sportster. Which is what we all asked for."

Web resource
For more info on the Sporster Go to http://rbi.ims.ca/3845-562