Now that Yamaha had finally switched to a 4-cylinder engine like its rivals, it was not only quick to catch up in the 4-stroke supersport category but soon went on to the next level of product excellence and quickly began leading the industry thanks to the famous XJ650 and XJ400 models. In 1980, the year that these two models were launched, Yamaha also released a 2-stroke model that would go down in industry history as an epoch-making machine—the RZ250.
The RZ250 could be called the equivalent of a statement by Yamaha: the 2-stroke supersport was back and wasn’t going to become a victim of the new era of emissions regulations and other factors as some were predicting. The reason the RZ250 was considered as such was Yamaha’s RD400 released in 1976. The RD400 didn’t have the aggressive character and feel that was a fundamental appeal of 2-strokes, and its performance was thought to have been muted in an attempt to imitate the milder engine character of 4-strokes. It was then that we began to hear murmurs about the demise of the 2-stroke.
However, at the same time, the TZ250, TZ350 and TZ750 production racers and the YZR500 factory machine that symbolized Yamaha continued to be top performers in the race arena. For fans that originally knew Yamaha as a 2-stroke manufacturer, many were unquestionably hoping for production models that were the embodiment of that racing image. Yamaha was also eager to respond to those expectations as best it could and keep the 2-stroke era alive. So, the decision was made to develop a new 2-stroke supersport model with the same liquid-cooled engine used on its race machines.

Having revived the 2-stroke supersport category with its RZ Series, Yamaha raised the bar once again with the introduction of the 4-cylinder RZV500R model [RD500LC for overseas markets] in 1984. However, the appearance of the TZR250 with its aluminum Deltabox frame in 1985 can’t be spoken of simply as a byproduct of the racer replica boom, and has to be described as a unique and exceptional development. This is because it went far beyond just the next evolution of the 2-stroke supersport to become an important model that would heavily influence the direction of state-of-the-art supersport handling as well as the future of 4-stroke big-bikes.
The big difference that separated the TZR250 development project from that of any other Yamaha models to date was that the factory race machine engineers at the time were brought in to work directly on the model. The Project Leader, Teruo Abe
(a member of Yamaha’s 2nd Project Engineering Division at the time), made the decision to have production model developers become members of the Racing Group he belonged to.
This resulted in the TZR250 using the aluminum Deltabox frame that had just recently been adopted on the YZR500 at the time, which essentially made it a YZR replica. However, the reason that this model deserves special mention is not because of how closely it resembled the YZR500.
It was the fact that the handling of the TZR250 was developed with the same approach as the YZR500. In order to explain why this was important, I first of all have to go back a few steps and talk about the path that the YZR500’s development had taken up to that point.

Like the other Japanese manufacturers, Yamaha had to withdraw its multi-cylinder, multi-geared factory machines from GP competition in the 1960s, but Yamaha alone remained involved in racing into the 1970s by supplying production racers. The company would finally make a full-fledged return to the World GP by making its first entry in the 500cc class with the YZR500 in 1973.
The first YZR500, codenamed 0W20, adopted a unique engine format that connected two in-line twin engine blocks side-by-side to form an in-line 4-cylinder engine. The reason behind this format was to make use of Yamaha’s proven 250cc in-line twin engine, while also opening up the possibility of feeding knowhow directly back into production model development. This same method was used later in developing the TZ750 by connecting two TZ350 engine blocks together.

This 0W61 was a machine for which Yamaha sought to include every specification thought to be advantageous at the time.
It was developed based on input from their rider at the time, racing genius “King” Kenny Roberts. One example of Roberts’ requests was to make the rear tire as wide as possible, and it led Yamaha to work with its tire supplier to develop an extra-wide race tire. For King Kenny, one of the few riders who could fully handle the increasingly powerful 500cc racers of the day, he most likely thought that as long as the tires had fantastic grip, he could apply more power while cornering.
He also probably felt that despite the high power the machine had finally achieved—and he was confident he could handle—it’d actually go to waste because the rear tire would start to slip.

After this valuable experience, the engineers developing Yamaha’s factory machines devoted themselves to the principle that “every characteristic of the machine must feel natural and in tune with rider perceptions.”
For the engine character of the next model they developed, the 0W70, instead of a blind pursuit of peak power, they began by seeking a character that would provide a smooth, steady building of power from mid-range speeds, even though it meant sacrificing some peak range power. With regard to the chassis, they sought a high level of rigidity while keeping the right amount of flexibility. In ways such as these, the development involved themes that were not very different from those of a regular road-going sports bike.
For the frame in particular, they worked from their base of knowhow concerning the structural shapes that provided good strength when using conventional squared aluminum pipes. To create a frame that had the right amount of flexibility when stress was applied, the structure was constructed of aluminum plates instead of pipes and the resulting Deltabox frame was adopted for the first time.
(Continue to Part 2)