The aim of using a small-diameter 16-inch front wheel as the representative feature of models in the early stages of the replica boom was to give the bike a light and sharp feel when leaning in to bank through a turn. Yamaha also followed this trend and adopted the 16-inch wheel, but they avoided giving their machines the excessively sharp handling of their rivals’ bikes. This was based on Yamaha’s belief that, unlike riding to the absolute limit in the world of racing, the general rider will feel greater assurance and enjoyment riding a bike with a handling character based on a feeling of stability, and in the end, that will enable them to ride faster. It goes without saying that the reason Yamaha bikes had the image of being good through corners and that the company was seen as the leader in handling performance from the 1960s was because Yamaha had always stuck to their policy of designing and building bikes specifically from a rider’s perspective. However, an era that threatened to uproot the very foundation of this Yamaha philosophy had arrived—the replica boom. The popularity spawned by this trend seemed to be never-ending.

“Yamaha was a latecomer to the racer replica category, so it was a very bold decision to adopt the concept of developing a production model that was essentially a racer, and go on an all-out offensive,” says Jiro Izaki, a key member of the development testing group (Yamaha’s Road Testing Unit, 2nd Project Engineering Division at the time of the interview).
However, Izaki never expected that this would force a decision about whether or not Yamaha should continue its signature approach to machine handling that it had maintained until then.
“Even when we were developing our early racer replica models, we still believed 100% in our traditional Yamaha approach that being able to ride with assurance was what allowed a rider to go faster,” confides Izaki. “We believed that this was the same with race machines. When it was decided that we would be designing a racer, we thought we should first try riding an actual race bike, so we test-rode the TZ250. But, I found the ride to be quite different from what I had expected,” he adds.

“Even if we were going to change our premise that stability be a top priority, there was still a feeling of responsibility to achieve our goals,” says Izaki. “But, no matter how many times we test-rode rival machines, the handling was just too light and quick for us to feel comfortable with. I just couldn’t enjoy riding them. We might get used to it riding where we knew what was waiting on the other side of a corner, like on a test track, but it wasn’t a ride that we could enjoy on winding public roads where the conditions always vary, and that fact bothered us. Our final decision was that we would aim for a feeling of lightness, but we would make every effort to avoid anything that made the bike’s handling difficult for the rider to get used to.
“In the bike reviews of motorcycle magazines back then, there were cases where they rated a machine’s handling as good, but when we test-rode it, we just didn’t agree.

“In line with the development concept of creating the FZR400 as a racer, it was decided from the beginning that we would be using an aluminum frame. This starting point already made the development approach different from our usual process. We would typically start by working out the frame layout based on the factors of what kind of rigidity and what kind of character we wanted the bike to have,” noted Izaki. “Since our factory machine had an aluminum Deltabox frame, we could rely on feedback from that. So, we had no second thoughts about what kind of frame we should use. Since the other manufacturers were using frames constructed with extruded aluminum, it might have been common course for us to explore that method as well, but because of our development concept to build a racer, the aluminum Deltabox frame was a must. Of course, there were other reasons contributing to this choice; we had a lot of development data from our race machines and being able to use that for developing things like rigidity balance with certainty was a big advantage.”

The FZR400 was composed of Yamaha’s latest features like the "Genesis" concept forward-inclined 4-cylinder engine, and that gave the bike a form that was truly that of a racing machine rather than a replica. There was also another major statement that would be made in the FZR400: the adoption of a low-profile radial tire. “We had used a radial tire on a mass-production model for the first time with the XJ750D,” Izaki said. “It was mostly just a strong determination to use a radial tire for the first time, and it was simply a matter of making a tire of the same size but with a radial structure. As you know [Nemoto-san], a tire with that kind of profile doesn’t really bring out the advantages of the radial format.”

A radial tire differs in that the cords in the carcass are laid in the lateral direction (90° angle to the center of tire tread, i.e. “radial” from the center of the tire), and bound over with specially constructed reinforcement belts laid in the direction of tire rotation. This construction gives the tire both sufficient strength and flexibility to maintain contact with the road surface, even when subjected to heavier loads. A radial tire of course also has the merits of a higher grip threshold and less tire wear due to friction. However, in the case of a motorcycle which can be leaned over unlike a car, the sidewall portion of the tire needs to be shortened as much as possible in order to take advantage of the radial structure. Furthermore, if the tire is designed with a wide tread, it becomes necessary for the wheel rims to also be nearly as wide as the tread because of the shortened sidewalls.
This caused a conflict for the motorcycle manufacturers. They wanted to have the merits of the radial tire, but they were also hesitant to adopt an extremely wide 4-inch wheel rim for 400cc class machines, which used a 2.5–3-inch rim as standard. Their resistance was due to the fact that such a wide rim would make it virtually impossible for owners to replace their radial tires with conventional bias tires of the same size later if they wanted to. This factor put a brake on the full-scale adoption of radial tires for motorcycles and prevented a more effective radial design for the ones that were adopted.

However, Yamaha’s goal was to make the FZR400 a bike with performance that would leave their rivals behind. So they didn’t hesitate to mount it with the same type of wide tires used on the race scene, as well as choosing advanced radial tires to do so. In this way, Yamaha pioneered the practical use of the first “low-profile” radial tire (the section height of the tire was 60% of the section width of the tire) that has come into common use today. “Of course, we developed that tire jointly with the tire manufacturer,” says Izaki. “At first however, it certainly wasn’t something that could be ridden with. What’s more, its problems were attributed to the fact that it was a radial tire. I remember becoming adamant about it, saying ‘We can’t possibly put tires like these on a bike for customers!’ The tire manufacturer was also being more cautious than was probably necessary, saying that because they were radial tires, the chassis and suspensions had to be specially designed to accommodate them.”

After successfully fitting the FZR400 with the first full-fledged motorcycle radial tire, the model entered its final stage of development. Izaki comments: “Right down to the very end, we had heated arguments over and over about the bike’s feeling of lightness. Compared to the almost feathery lightness of our rivals’ models, some people in the company were saying that ours wasn’t sharp enough and that the response was dull or heavy, and the fact that they weren’t used to the great stability that the radial tires provided only compounded such responses. Although we weren’t as fixated on stability as usual, we still weren’t willing to compromise on our determination to ensure that the bike feel reassuring to the rider.”
Compared to other Yamaha bikes until then, the FZR400 that was released on the market was actually lighter in handling and more agile at times like when beginning to lean into a turn. But they hadn’t given it the kind of quick handling that the rival machines had, so it somehow felt like it had a more stable and composed ride character. Furthermore—although it‘s hard to include this as part of an evaluation of a bike’s handling—the benefits of the radial tires were very palpable, such as the feeling of stability during cornering akin to a big bike, and the awesome braking performance that still felt very stable.

“We also used suspension settings with a deeper compression stroke and longer rebound stroke that made the ride feel soft. This was another thing that people in the company were saying wasn’t ‘sporty’ and that the bike didn’t feel like a racer replica. But, it had a feeling of stability and was easier to control, and even if the tire did slip, the longer rebound slowed the motion and gave the rider more time to make a recovery. That’s why we can’t rashly decide to give a bike settings that make the suspension too hard,” concluded Izaki.
Back then when tire grip—a big factor influencing riding ease and control—had dramatically improved [with radial tires, etc.], it was probably becoming difficult to find a clear performance difference using just the suspension settings when testing was done on a full-on circuit. But if we take World GP riders as an example, the ones who are really championship contenders will typically choose suspension settings that give a longer rebound stroke but the lowest possible setting for damping. This is because World GP riders have the skills to react to something happening due to the soft suspension settings, but they have to depend on the suspension when recovering [from wheel slipping and the like] when riding near a bike’s performance limit. This was a conclusion reached by veteran racers that rode under some of the toughest racing conditions.

“It’s a fact that we were unable to establish a clear advantage over our rivals on the track. But when you took the FZR400 out on winding roads, its handling as well as its engine character, made it very fast. As far as we were concerned, we had done what we’d set out to do,” said Izaki. “Looking back now, the market and the manufacturers were both leaning in the same direction at the time. Even we were running tests using racing slicks since we knew from the development stage that the FZR400 was going to be used in racing. But now, I believe that it would have been wrong to develop a product that we would have to tell users, ‘It’s actually a bike that’s most fun to ride on the circuit.’
“Even though we’d always believed that we had to develop bikes that were fun to ride, I think everyone was suddenly starting to get carried away with a bike’s ‘image’ instead. I felt that the whole motorcycle world was getting lost in admiration of scenes of dragging your knee on the pavement when cornering. But, I also knew if that was all we offered them, the users would eventually start to shy away from such products,” recalls Izaki.