01. People Ride It For Fun

When people think “development”, they often picture styling and design. But there’s another crucial part of the process: evaluation.
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Inside Yamaha’s First Vehicle Experimentation Department (YZ Gr.), evaluation means riding the bikes—testing engines and chassis in the real world, then judging what works, what doesn’t, and what needs to change. The team looks at outright performance, but also durability and functionality, chasing the balance a motocross bike demands in heat, water, dust and everything in between.

Sato Shori knows that balance well. A former All Japan Championship International A-class rider in the 1990s and 2000s, Sato later joined Yamaha Motor Co., Ltd. and has spent years testing YZ chassis.

He explains that designers can predict durability to a point through desk studies and strength evaluation. But ride feel is different—because the rider’s senses matter when you’re shaping how a frame behaves.

When a new frame is being developed, the team begins with something close to the previous model, then focuses on what the market is calling for. If, for example, they’re aiming to reduce vertical reaction, they may ask the designer to start with a base concept that lowers vertical rigidity. From there, the refinement becomes painstaking: experiments, sensory evaluations, and sometimes literal hands-on fabrication—adjusting plate thickness and shape by cutting and piecing components together. And the maddening part? Tiny changes matter.

A patch as small as 1–2mm can create a difference too subtle to identify through analysis or bench measurement—but a rider can feel it. That’s why, for Sato, compromise isn’t an option.

His reason is simple: the YZ is built for people to ride and enjoy. The numbers matter, but so does feel—so the team keeps working to blend the designer’s intent with human sensibility.

Using experience and intuition, they shape and re-shape parts, then bring in contracted riders to test and comment. The loop continues until they land on the best solution.

Once the Japanese base specification is ready, it’s checked in North America—the key market. Feedback from riders across regions is used to find an “average” feel that works broadly. If the frame balance isn’t right, suspension settings are revised. If that still doesn’t solve it, the team revisits the frame again—then the suspension again—repeating until the whole package lands where it needs to be. Even details like engine brackets and other components are reconsidered, down to materials, thickness and shape.

The target? A bike with “gentle reactions”: confidence into corners, clear traction when accelerating, and easy-to-read feedback from the track surface—so riders can push without hesitation.

Through all of it, racing remains a compass. Sato follows All Japan, world championships and AMA. Racing teaches, reveals trends, and shows where rivals are heading. Fall behind by even a step and catching up can take a long time—so the team watches closely, not only Yamaha’s machines but competitors’ too. And yes, the goal is still to win.

Sato admits the biggest motivation is seeing the bike they built take victories—and if that leads to strong YZ sales, even better. The AMA Supercross and Motocross wins in the USA this season have given the development team confidence, and momentum to keep evolving the YZ even further.

The Stories

2. An Engineer Who Never Stops

If the frame is the bike’s skeleton, the engine is its heart—and Kitahara Naotetsu is the coordinator overseeing the full scope of YZ engine evaluation. Engine testing isn’t just ride feel. It includes measuring engine-only performance, checking functionality (oil circulation and pressure), evaluating reliability through durability tests, measuring noise to meet race regulations, assessing starting, and more. Kitahara describes himself as a “jack-of-all-trades”—someone looking at everything, managing everything.

3. Chasing Artisan-Quality

Welding rarely gets the spotlight, but for Otohito Yamazaki—an engineer with deep welding expertise—it’s a core part of YZ450F quality and reliability. Yamazaki first became involved with the YZ more than 20 years ago, around the launch of the YZ450F. After time working on supersport models like the YZF-R1 and R6 and handling frames for overseas models, he returned to the YZ—setting and resetting welding on the assembly line, touching up welds, and performing final inspections. He moved into his current department four years ago.

4. Guardians of Quality

Takayanagi Kenji works in quality control. His role is to establish, maintain and manage quality standards for each new-model assembly process. He plans and implements measures to prevent defects and recurrences, and drives improvement activities by analysing quality data. Two influences led him to Yamaha Motor. One was his older brother, who worked for the company and was involved in motorcycle inspections. The other was personal history: Takayanagi attended Yamaha Motor’s soccer school as a child—back in first grade, over 30 years ago. That familiarity helped shape his desire to join.

5. I Love My Job

The YZ series of motocross competition models is sold globally—strongest in North America, but also spanning South America, Europe, Oceania and Asia. The riders are just as varied as the map: professionals in AMA Supercross, the Motocross World Championship and All Japan, plus weekend riders enjoying family rides or solo sessions. Some stay with YZs for life. Some ride them simply because it makes life better. And the YZ, in turn, is built by people inspired by those riders.

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