Racing Revolution

RACING REVOLUTION

IN 1973, WHEN YAMAHA two-strokes were the first to win 500cc Grand Prix races, it was a remarkable achievement because they won not by superior power but through the improved handling of long-travel Monoshock suspension.

Even before this, Yamaha had established itself as the preeminent racing manufacturer by offering for sale production racers such as the TD1, TD2 and TD/TR3, which had become the normal tools of professionalism for a new generation of riders.

Now the two-stroke era in top-level GP racing has ended with the adoption of a 990cc four-stroke formula. To showcase what has been accomplished in the 30 years between, Yamaha’s Communications Plaza in Iwata, Japan, presented a display, “The 30-year Evolution of the YZR500.”

I attended this presentation with other journalists last fall, and wandered from one YZR500 model to the next in a state of sensory overload-heightened by the presence of factory engineers. One engine was presented with a cylinder head removed, allowing me to look in at the two-layer Powervalve exhaust-gate system.

Powervalve, by changing exhaust timing with rpm, overcame the two-stroke engine’s otherwise narrow powerband. All other makers quickly adopted it in various forms.

Early YZRs with steel-tube frames and wire wheels gave way to cast wheels in the 1970s, aluminum tube frames in 1980 and the now-familiar twin\ aluminum beam, or Deltabox, chassis in 1983. The evolution of this concept could be seen by walking along the timeline of machines and noting that as the top frame rail became deeper, the downtubes atrophied away into mere engine hangers. Such chassis are now the type most widely used by major motorcycle manufacturers.

The growth of tire width, and of chassis stiffness with it, could also be traced in this manner. Single-shock rear suspension evolved while forks became stiffer and more capable. All these developments, evolved in response to the compact, sudden power of two-stroke racing engines, have become gifts to the modern four-stroke production motorcycle.

Yamaha’s 30 years of 500cc GP racing produced countless wins, championships and memorable champions, but the most lasting result is that they developed the major features of the modern, highcapability production motorcycle. -Kevin Cameron