As I had mentioned in the earlier article on Yamaha FZ16 Midship Muffler, here is the next piece of content on the bike’s radial tyre. If you want to read the original review visit, Yamaha FZ16 Road Test and Review.
The Radial Tyres of Yamaha FZ16: This is the first radial tyre ever featured as a standard equipment on a bike in India. A radial tyre has a construction in which the cords of the structural structural skeleton of the tyre, known as the carcass, run radially around the tyre at right angels in the direction of forward motion. The structure gives the tyre excellent firmness and prevents excessive distortion of the tyre’s shape due to forces from the road, reduces rolling resistance and helps improve fuel economy. Most people know the heavy, woobly feeling while riding on a bicycle with low air pressure in the tyres, and when the tyres are fully inflated there is little distortion in its shape, even when going over bumps on the road surface. That is what is meant by low rolling resistance.
We asked the Yamaha engineers about the actual user benefits that comes from this radial tyre. “The FZ16 has been developed with the aim of going beyond the conventional commuter bike to achieve true sports bike performance that offers the owner real fun of riding. As one of the ways to achieve this goal, we adopted a radial tyre for the excellent firmness it provides. To optimize, the balance between the tyres and the frame, we also adopted an extra sturdy front fork with thick 41mm diameter inner tubes.” We began by asking about more detail on the merits of a radial tyre. “Because of its excellent rigidity, a radial tyre can be designed with less tyre height. And because the tyre is thinner and flatter, it weighs less. The size of the radial tyre on the FZ16 is 140/60-R17, compared to an equivalent 120/70-17 bias tyre. And, although it has roughly the same diameter, it weighs less than the biastyre. This also means lower inertial mass at the rear axle. You might compare this to the feeling of wearing light sneakers as opposed to heavy shoes.
Another benefit of radial tyres is that their added firmness means that even a fatter tyre provides a firm ride with a sharp handling response. Generally speaking, a fatter tyre tends to flex under pressure and therefore does not give a sharp handling feeling. But a radial tyres inherent firmness means that even a fatter tyre there is a quicker convergence of external forces, which means sharper handling and a sportier, more agile ride. It is a tyre that provides a solid feeling of road contact.
To develop the radial rear tyre for the FZ16, Yamaha’s design staff worked closely with the technical staff of the tyre maker MRF and exchanged information numerous times about the exact performance qualities they wanted for this model. The specifications of a custom designed tyre like this involves more than just the various size dimensions. This also involves longitudinal and lateral rigidity balance, grip qualities and flexing (distortion) characteristics and a mutual balance amongst these various factors. Of course, it is not this tyre alone that gives a bike like the FZ16 a sporty, agile ride. Adjustment of the specs of the various chassis components to achieve an optimum mix is also necessary to bring out the maximum performance potential. Here is what the Yamaha engineers had to say about the chassis development: “The FZ16 frame is a newly developed diamond type frame. Viewed externally, it may look similar to the frame of the Yamaha Gladiator, but in fact it is completely different and was developed wfth a prime focus on reducing weight. Also, rigid mounts were used instead of rubber mounts in a design that makes the engine function as a structural member of the frame.
Then we worked on achieving the best specs for the many related parts and components in detail, through repeated tests. The stay that holds the engine (cylinder) head to the frame are made of steel plate with a thickness of 3.2 mm and high-rigidity die-cast Aluminum was used for the parts that connect the pivot assembly to the frame. These parts are especially effective in providing quicker convergence (absorption) of external forces when running at higher speeds. Also, a hard rubber close in consistency to plastic resin is used for the rear hub damper to increase rigidity. This combines with the effect of the rear radial tyre to make this a machine that achieves excellent response to the rider’s handling actions.
In simple terms, you won’t feel any “sloppiness” in the handling response while riding through traffic on the city streets. Instead, you get a response that enables agile riding. The FZ16 has a chassis performance that provides direct response to the rider’s throttle work, and at Yamaha we call this, “drivability with a feeling of directness.” And it is part of their definition of the fun of riding that they want this model to deliver. Another important chassis feature of this model is the extra sturdy front fork with thick 4lmm-daimeter tubes. The 41mm inner tubes of this front suspension are the size usually used on 400cc class sport bikes. Why did Yamaha choose such a high-spec unit? “Besides, its shock-absorbing function, the front fork is also a component that determines the overall rigidity of a motorcycles chassis. To achieve the optimum balance with the new frame and the radial rear tyre, we chose a unit with 41mm tubes to achieve a high level of rigidity.
In addition to providing good rigidity and stability in straight-line running, it also functions especially well to give a good, solid feeling of machine stability on rough roads with continuing bumps and during sharp braking,” the Yamaha engineers comment. That’s not to mention the distinctive look it gives to the bike’s appearance. And, the larger spec also improves the fork’s suspension function. “These thick inner tubes improve the mechanical functioning of the suspension. If you have two suspension units with the same cushioning capacity, the one with the larger inner tube circumference will function better, because the increased surface area reduces the friction per unit of surface area and thus produces better response. Of course, the larger diameter also means that you can give it a larger diameter spring as well. With the FZ16s front fork you wont feel any “bottoming out” when going over bumps or during sudden braking because of the strong, solid cushioning function it delivers”.
The fatter fork may look heavier but that is only the visual impression. “This fork uses tubes with thinner walls to reduce weight, and the handlebar crown that supports the fork is also a lightweight cast Aluminum unit. The design of the ribs on the inside of this crown was also optimized by conducting repeated tests. The specs of the fork offset, caster and trail were also optimized in relation to each other to help contribute further to the enjoyable and highly stable handling feeling”. Another characteristic you will notice with the handlebar crown and the under-bracket on the FZ16 is the wider breadth of their span. They are about 10mm wider than those on the Gladiator and this surely contributes to the stability of the front assembly.