Motorcycle Function and Fashion

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Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>. (Robert Martin/)

I have written before of how the functional features of 1950s–'60s dragbikes, taking root in the imaginations of spectators, took on a life of their own as the chopper. Dragbikes needed to be long and low, with lightweight brakeless front ends raked out for high-speed stability, their engine back against a wide rear tire, and fuel supplied by the smallest, lightest (peanut) gas tank at hand.

More recently came “streetfighters.” They owed their origin to young European sportbike riders who, upon crashing, found they couldn’t afford to replace the plastic bodywork. (Battles create casualties, right?) The result was a different kind of sports motorcycle. I’ve always wondered; against whom do the streetfighters fight? The little old lady from Pasadena?

Even today, the romance of first-generation (late-’70s/early-’80s) Superbikes resonates with many custom builders, leading manufacturers to cash in with naked sit-up look-alikes featuring blacked-out, liquid-cooled engines in place of the 1,000cc air-coolers of the originals. At the time, Superbike rules required the “silhouette” of the production bike to remain unchanged, dictating their simple, 1960s-inspired style; think of bulbous-tanked classic Triumphs or BSAs. Their carburetors were in plain view, not yet swallowed up into a gas tank evolving into an intake airbox, the carbs themselves not yet evolved into fuel-injection throttle bodies. God was in his/her heaven and all was right with the world.

Wobble, Weave, and Braced Swingarms

When those bikes were breathed upon to make 130–150 hp, they moved right along—fast enough to reveal the shortcomings of their narrow, hard tires and lawn chair chassis. I saw them in procession around the turn 9 “Carousel” at California’s Riverside International Raceway in 1977. Every one of them was weaving. That in turn led to bigger, stronger forks and swingarms braced against wheel tilt, all in hope of settling down racetrack twitches and wobbles.

Velocette’s first swingarm was just three pieces of pipe, a money-saving construction that persists to this day in low-powered bikes. But in that classic first Superbike era such designs flexed every which way, forcing the AMA to enact the rule that “Swingarms may be modified or replaced” to protect riders.

The braces were triangulated structures of round tubing welded either above or below the existing swingarm. That simple idea, between then and now, has evolved into today’s all-sheet swingarms, big stiff boxes that do a fine job of holding rear wheels in the central plane of the bike.

This is irrelevant to custom builders, whose goal is to evoke a certain era or align with a chosen aesthetic. And it turns out that a whole aesthetic of custom-modified swingarms has resulted. There are disciples of the rectangular-tubing school, attracted to the linear severity of extruded beams, and there are devotees of the round-tube movement. Some place the bridgelike welded stiffening atop the arm, some below.

In the present moment, builders of swingarms for high-performance use have little choice but to locate the reinforcement under the swingarm. As conventional fuel-tank volume has been given to the engine’s intake airbox, the fuel has been displaced to the rear where it now forms a “foot” growing rearward under the rider’s seat. This in turn leaves no room above the swingarm for bracing structure at full suspension travel, so that structure has retreated to the underside.

The Era of Eccentric Chain-Tension Adjusters

Some builders are especially charmed by the brief period of big eccentric chain-tension adjusters, located at either the front or rear of the arms. Eccentric chain adjusters arrived in Superbike because they were robust, but they were soon gone because at each adjustment of chain tension the bike’s anti-squat behavior was altered (depending, as it does, upon the angle between the tension side of the chain and the central plane of the swingarm). But are we surprised if artists with TIG torches care little about a bike’s midcorner attitude changes?

Same with swingarm droop angle. Honda in 1988 gave its NSR500 racebike a horizontal swingarm from the team of engineer Kazuhiko Tsunoda. Oops! Instead of smooth corner exits, that bike squatted down and pushed its front end, heading for the outside. For the custom builder this means nothing: if a horizontal swingarm looks right—or even one that slopes down to its pivot—that’s what gets built.

The process by which function leads to fashion is very simple. An innovative element is added to the motorcycle for sound performance reasons, but onlookers’ eyes are attracted to it because of its novel visual appeal. I think of the car dealer who funded a top-fuel team; he loved the ritual of the crew chief running a hand over the open ends of the zoomies. At the drags, the car’s engine was running and the chief was checking to be sure all cylinders were firing. But the sponsor saw only the theater of it, and did it when the engine wasn’t running at all.

Building for performance limits choices to those that work, but building for looks allows the imagination greater freedom. Engineering can become a form of prejudice that stops new ideas from being tried. Some engineers scoff at artistic imagination, but which was Massimo Tamburini, creator of Ducati’s 916? Engineer? Or artist?

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