Imagination and the Prison of Physics

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The ’80s and ’90s saw vast advances in sportbike performance as racing pushed sales floor success. (Honda/)

Until the sportbike era (the 20 years between 1988 and 2008) production motorcycles were remarkably free of the heavy hand of physics. Physics became important only at the extreme edges of performance, a zone seldom visited by most riders.

That all changed when sales of the new sportbikes, from the mid-1980s onward, were seen to depend strongly on winning Supersport and Superbike roadraces. Manufacturers had tried to make their bikes win the new Superbike Production races of the later 1970s, but it was hard going because those bikes combined the novel high power of 1,000cc four-stroke engines with 1960s chassis, suspension, and tires. It was all uphill to make those bikes work while honoring production racing rules.

There was little wrong with 1960s bikes, which did their jobs well so long as power didn’t overwhelm what the chassis of that time could handle: about 40 hp. People had great fun on those bikes, and covered a lot of ground. Many today look back on the straightforward style of the Triumph Bonneville and Harley Sportster with real affection.

Japan, despite its snarling Kawasaki Z1 and Suzuki GS models, had to eat the humiliation of seeing the first American Superbike roadrace championship won in 1977 by Reg Pridmore—on a European BMW twin.  The chassis of the big new four-strokes from Japan, overwhelmed by more than 100 hp, weaved so badly at speed that their large top-speed advantage couldn’t be used.

Reg Pridmore on the Butler & Smith BMW. (Cycle World Archives/)

Engineers needed a fresh start with production bike chassis design. Bendy pipe chassis, skinny hard tires, and door-closer rear shocks of the 1960s couldn’t be made to win the races that would publicize and sell the bikes. The sportbike revolution of the 1980s was the result.

Engines and riders were moved forward to keep front tires steering during acceleration. Steering head angles were steepened to speed up steering. Chassis took new forms and were stiffened to accurately transmit the large forces of control and suppress instability. Swingarms, which since 1950 had been just three little pieces of pipe welded together, suddenly grew bridge-like triangulated bracing. Wider rims on cast wheels; larger-section tires of softer, grippier rubber; stiffer fork tubes and serious brakes were forced into being. These tools restored the balance between engine and chassis.

Physics had taken over the design of motorcycles because racing had become central to selling product. Success in racing requires design to focus on performance. Physics ruled. The stylists were left to choose the colors, decorate fairings with scoops and darts, and shape functionless parts such as seat backs and airbox covers.

As middleweight naked bikes and twins (like the KTM 890 Duke R) are now grabbing the attention of buyers, where does physics fit in? (KTM/)

Now that’s finished—sportbike sales have nearly zeroed, and other than the basic needs of safety and reasonable function, styling is no longer the vassal of physics. Middleweight twins have our attention, showing the now-universal humpbacked outline and powerful influence of KTM’s Kiska design and their future-themed origami shapes. The sportbike years expanded the technology of the motorcycle, but now it has become general knowledge.

Will imaginative designers please come forward to show us new possibilities?

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