Aprilla Mille
Yet while the parallel-twin is relatively inexpensive to build and compact compared with other engine configurations, it has shortcomings. The V-twin's pleasant character is largely absent in its parallel cousin. Rather than residing in the plane of the bike's centerline, inTurner's design vibration rocks the engine from side to side. Commonly known as a rocking couple, these forces stem from the spacing of the crankpins relative to the crankshaft's centerline.
Norton was the first manufacturer to effectively squelch rocking-couple vibration, isolating the engine, transmission and rear wheel from the rest of the motorcycle with rubber mounts. Other manufacturers have subsequently used balance shafts to quell the parallel-twin's inevitable quaking. And while the solution yields good results, such engines tend to be bland compared with multicylinder engines and more advanced V-twins. All of which proves that while it is entirely possible to obtain perfect dynamic balance, it can be done without achieving perfect smoothness--or even the desirable kind of character.
Triumph Bonneville
Still, after more than a century of development, the V-twin still offers the greatest adaptability to the widest variety of roles. For example, the overwhelming majority of customs/cruisers have kept the classic V-twin architecture, just as they have since the first fender was bobbed. In fact, according to Motorcyclist's 2004 Motorcycle Buyer's Guide, 94 percent of cruisers and touring bikes are powered by twins, and 86 percent of those are V-twins. Likewise, more than half the '04 sportbikes, sport-tourers and standard bikes for sale in the U.S. are twins, and some three-quarters of those V-twin-powered. Although displacement, power and torque have skyrocketed during the last century, V-twins have made the most of their inherently relaxed, satisfying cadence as cruisers and tourers.
In sportbikes, V-twin engines have become true fire-breathing monsters that dominated World Superbike racing for 15 years. (Shifting rules have kept the V-twin from dominance in AMA Superbike racing, however.) Success on the world stage just demonstrates that V-twin Superbikes (and their street-legal counterparts) are some of the best-performing motorcycles ever built. What's more, the nature of their power remains linear and controllable. Sporting V-twin power has almost always been friendly. Contemporary examples show it's now an exceedingly muscular friend.
But twins have the power to be more than motorcycles. Indeed, twins have put entire corporations on the comeback trail. For example, V-twins are responsible for Harley-Davidson's extraordinary success. V-twins carried Ducati from its low point as a Cagiva subsidiary to unprecedented racing success as an independent and financially stable company. Opposed-twins have sustained BMW's motorcycle group since the '20s. Triumph's legacy as the originator of the four-stroke parallel-twin was celebrated by a new '01 Bonneville.
1911 Harley-Davidson F-Head
Such performance--both on and off the bike--is what makes twins in general, and V-twins in particular, so extraordinary. From its simple, innovative beginnings as cheap transportation, the V-twin has become an icon. No other engine configuration is as light or compact, yields such a short, rigid crankshaft or bolts so elegantly and intelligently into a motorcycle's chassis.
Whereas the march of technology seems to have contributed to smaller, more tightly defined niches, it has also expanded the V-twin's capability and utility. Having become more powerful, smoother and more sophisticated, it has adapted to a broader range of duties, even as motorcycling has become more specialized.
Plainly, the V-twin has stood the test of time. With any luck, it will continue to do so for another century--or two.