Yamaha aims to maintain its position as the leading brand in all the sectors it is involved in, including in the off-road industry.
Prologue
The all-new YZ450F which this story introduces is the flagship model of the Yamaha off-road world.
The first-generation YZ400F, equipped with a four-stroke engine, was unveiled in 1997. This model led the trend towards four-stroke engines in the off-road racing scene. Released in 2010, the YZ450F was equipped with a new engine featuring a unique layout which included a forward-positioned intake, a rear-positioned exhaust port, and a rearward-inclined cylinder head. After this, the refined design of the YZ450F received high praise from the motocross scene, and its high performance and usability allowed it to achieve the number one ranking in both market share and unit sales in America, the home of motocross.
The new 2018 model YZ450F features an engine characterised by high power and usable output, and a further-evolved chassis delivering good traction performance and high shock-absorption.
Created through distilling all of Yamaha’s advanced technology and race-bred knowledge, the new YZ450F is unmistakably powerful, yet lighter and more usable than ever before. In this story, we would like to share the secrets of its development with you.
Engine
The major point of discussion around the engine has to be the addition of the electric starter. This was a big decision, but we decided to make it standard as a function ultimately necessary for racing. All aspects of the engine have been newly designed, including the cylinder head, the cylinder, the crank case, the piston and the cams. Therefore, while the concept of this engine is refined, the results of the new design far exceeded a simple progression, and it is no exaggeration to say that we have created a completely new engine.
What was demanded of this engine was overwhelming power and usability.
Since the 2010 model, the YZ450F’s unique layout has refused to follow the beat of anyone else’s drum, and it continues to hold an advantage in engine performance over its rivals. For the new model, we have improved engine performance while simultaneously pursuing usability. The key points in delivering usability are the engine responsiveness to acceleration inputs, and the characteristics of engine output as it responds. At the same time, its relationship with the chassis, which includes the frame that holds the engine in place and conveys the power to the rear wheel, is crucial.
The angle on the YZ450F’s characteristic rearward-inclined cylinder has been changed from 8.2° to 6.2°; in other words, the cylinder has been made more upright. This was done with the goal of increasing forward weight on braking when entering a turn, and giving the body a more stable feel. We will look at the body in more detail later, but this creation of a higher level of synergy between the engine and the body has been a significant theme in this new model.
The cylinder head has seen a change in the shape of the intake and exhaust ports. We have moved to high-lift cams, and changed the valve overlap from the current 68° to 76°. We have made advancements in performance at high RPM, as well as in usability. The new-design piston has been strengthened by optimising the shapes of the ribs around the reverse side piston pin-holder. Thanks to this, we have been able to reduce the stress on the upper part of the piston, which has resulted in a reduction of thickness in the piston top, and has succeeded in lightening the piston itself. The weight has been reduced by just 6g, but in an engine that can run at 10,000 RPM or more, the effect is much greater than the numbers would lead you to believe.
The clutch’s pressure plate has also been significantly reduced in thickness. While it does retain its rigidity, by carefully selecting the area to reduce in thickness the pressure plate now bends in just the right way when operating the clutch, which has improved the clutch feeling, and specifically the feeling when riding the clutch. Because we understood through past developments that raising the precision of the pressure plate’s sliding surface had led to improvements in clutch feeling, by changing the shape of the pressure plate (in addition to increasing precision) we aimed for another level of improvement in the feeling in the new model.
We also revised the area surrounding the transmission to suit the more powerful engine. While there was no change to the gear ratio or the size of the transmission unit, by increasing the gear tooth thickness by 1mm for the frequently-used 2nd, 3rd, and 4th gears, reducing the length of the shifter by 1mm, and optimizing the shape of the dog, we have improved shift feel as well as reliability.
We also changed our fuel ignition supplier to MIKUNI CORP. We successfully lightened individual throttle bodies by approx. 60g. The new model comes equipped with a lithium-ion battery specially designed for the YZ450F, a first for Yamaha motorcycles. This change to the battery alone has resulted in weight reduction of approx. 1.4kg compared to the previous model. The lithium-ion battery is not only lightweight and compact, but also powerful, and while on the one hand this battery features low self-discharge, its maintenance method also differs from that of lead batteries. It was because of this that we added a battery management system which constantly monitors the battery’s status so that it can be used safely.
The addition of the electric starter is also a major advance. There were, of course, a number of differing opinions surrounding this feature. Because the YZ450F is our flagship off-road motorcycle, it is certainly essential that the new model has an increased symbolic significance, but more importantly, that it is a motorcycle which can win races. Given that, the addition of the electric starter was not a simple matter from the perspective of either weight or space. However, quickly getting back in the race after falling is also a crucial factor in racing. Thus, we determined that an electric starter which enables an easy return to the fray after an engine stall should be considered vital racing equipment. We therefore made the decision to add this new feature.
The functionality of the electric starter is identical to the electric starter in the cross-country model, the YZ450FX. However, this electric starter was newly developed specifically for the YZ450F. It features high output belying its compact size. However, even while it is smaller, the cell motor itself is still heavy. For this reason, we came up with a layout where it was placed behind the cylinder, with the goal of mass centralization. Not only is there not much space available there, but the exhaust pipe also runs through the area, making it very hot. However, that was the only possible location, and so after numerous discussions with the designers, we decided on the best location and installation method.
Another new development is the updated power tuner, which changes the engine’s output characteristics. In the past, a dedicated device was connected to the bike through a cable, however we have developed the new power tuner as a smartphone application. Using your smartphone's Wireless LAN, you can now make adjustments with the power tuner without the need for a cable. The app is of course available via free download in both iPhone and Android versions.
Another benefit of the transition to an app is a significant increase in the power tuner’s base functionality. There are various mapping tables for fuel injection volume and ignition timing, and both throttle opening on the vertical axis and engine RPM on the horizontal axis have been subdivided from the current 3X3=9 matrix to a 4x4=16 matrix. The throttle opening and engine RPM scales, which have been fixed in the past, can now be changed freely. By doing this, not only is it possible to display any maps that are created in 3D, as well as expand them and check them in 360° view, but changes to settings are reflected in real-time within the 3D map, and settings can be visually checked as well.
The functions displaying logs for engine RPM while idling, oil and water temperature, accelerator opening etc. have been retained from previous models, but are now also equipped with a maintenance timer function, enabling optional setting of items such as the piston and engine oil. It is also possible to share settings data over the internet. We are also currently working on exciting plans to see whether it is possible to distribute the settings data for elite riders using this function.
Chassis
Along with the engine featuring a forward-positioned intake, a rear-positioned exhaust port, and a rearward-inclined cylinder, the 2010 model adopted for the first time a bilateral beam frame made from aluminium, which was welded together with the steel engine, creating an integral unit from the different characteristics of aluminium and steel. Through the optimisation of the balance of flexibility between strength and rigidity, we pursued traction performance which conveys all the engine’s power to the back wheel, a high degree of shock absorption over dips, a high degree of straight-line stability, nimble handling, as well as compactness.
While the new frame does not differ from the base concept, for this model we added weight during development to specifically improve shock-absorption over dips. The front of a bike becomes heavier when decelerating to enter a corner. However, the centre of gravity moving forward causes balance to worsen, making the body unstable. At this point, if the bike can handle the weight added to the front and absorb the shock with the suspension and frame, even if going over a dip, then the bike can enter the corner with its stability intact. Like on-road motorcycles, the disposition of the body of off-road motorcycles also changes through the sound application of weight to the front, allowing them to quickly clear corners. The new YZ450F actively aimed to add weight to the front as part of its normal operation. It was in order to increase forward weight that we set the cylinder to be inclined rearward, and reconstructed the rigidity balance of the frame.
Specifically, while the fuel tank rail that stretches from the steering head to the swing arm previously depicted an S-shaped silhouette when viewed from the side, for this model we joined it in a straight line. We also changed the position and shape of the sub frame which joins together the fuel tank rail and the down tube. We also discontinued the engine mountings set into the sub frame, and instead extended a new-shape bracket from the rear of the fuel tank rail, mounting it on the upper part of the transmission. Widening the spacing of engine mounting positions allows the frame a greater degree of flexibility, which enables higher shock absorption using the whole frame when riding over dips. In fact, this new engine mounting position was also adopted as the factory specification in the YZ450FM, which battled it out in the IA1 class of the 2016 All Japan Motocross Championship. It also had the same aim.
We also developed suspension in collaboration with supplier KYB Corporation, and made major improvements in potential. The cylinder diameter of the front fork was expanded from 24mm to 25mm. This makes it possible to receive even higher damping forces. As we did this, we also changed the high-speed valve, which applies damping in the middle speed range, from a coil spring to a valve shim. Following performance when switching damping from pressure to extension, or from extension to pressure, has been raised to the next level.
We provided greater stability to the rear suspension’s damping force by increasing the capacity of the reservoir tank. Newly-developed lightweight springs were also used, which successfully lightened the bike by approx. 300g through making the wire diameter finer. Even with the same spring rate, the ride-feel will change based on the materials that the suspension springs are made from. With that in mind, we created springs from diverse materials, comparing them to create the perfect balance of lightening and ride-feel.
In addition, by adjusting the thickness of the handlebars, we succeeded in lightening the bike by 100g without sacrificing controllability or direct responsiveness. Employing new lightweight rims of a different shape front and rear manufactured by Daido Kogyo Co., Ltd. we improved the feeling of traction and shock absorption over dips, further lightening the weight by approx. 100g. We have also adopted a new lightweight drive chain manufactured by Daido Kogyo, which features reduced the thickness of the outer plates through careful attention to the manufacturing method and shape, ultimately succeeding in further lightening the bike. Finally, we have shifted to a new lightweight fuel tank with a reduced capacity tailored to motocross racing, thereby achieving further weight saving. All of this, coupled with an uncompromising focus to many different areas of the new motorcycle, has successfully delivered significant weight reduction.
Design
We also updated the body design. All the members of the design team are excited about how cool it looks, and are very proud of the design. The most significant feature is how we have managed to emphasise the horizontal line symbolic of the YZ series. In recent years, the skill of riders in off-road racing (as well as the potential of the motorcycles) has been increasingly significantly, which has led to both motorcycles and riders moving in a more aggressive manner. The horizontal line symbolic of the YZ450F stands out boldly among the three-dimensional movements of the rider and the motorcycle, which highlights the motorcycle’s lightness, manoeuvrability, and high performance. By lowering the lowest part of the seat centre by approx. 8mm and the rearmost part of the seat by approx. 20mm compared to the previous model, we have emphasised the horizontal line both visually and sensationally.
By changing the shroud shape in addition to narrowing the front of the seat by 9mm on both sides, we significantly slimmed down the area from the inner thigh to the knee while the rider is seated. The simple act of slimming the body is enough to stir up the imagination of the rider. This has led us to create surfaces with very little unevenness, so that the rider’s boots and knee-braces are less likely to snag when they move. One highlight is the change in the material of the side cover which wraps around the silencer to the stronger and more heat-resistant polyamide resin, which also allowed us to incorporate the side cover inside the body.
As the surface of the radiator shroud which the rider’s knees fit around has been redesigned to be slimmer, but span outwards, the shroud opening at the front of the motorcycle has been expanded to take in more of the air rushing past, which together with the revised radiator layout increases the cooling effect. At the same time as achieving a compact design for the exterior parts, we were also able to emphasise lightness and strength through the new-design front fender evoking the overall structure, and the rear fender which includes ribbing.
Epilogue
The aim of the YZ series has not changed since its creation. That aim is to be a powerful, lightweight, compact motorcycle with characteristically usable output and a well-balanced chassis. The ideal image that the series has strived for has always been constant, even at the creation of the YZ400F with its four-stroke engine, even for the YZ450F with its increased exhaust capacity, and even upon the creation of the 2010 model - the YZ450F - with its engine featuring a forward-positioned intake, rear-positioned exhaust port, and rearward-inclined cylinder set in a bilateral frame.
However, looking back, as our rivals evolved, there was a need for us to respond with higher aims by evolving ourselves, which made it possible for our technical abilities to catch up with our aims. And so now we have created the 2018 model YZ450F, a product of Yamaha’s leading-edge technology and race-bred knowledge, and the expression of our intent to continue setting the pace in off-road motorcycles.
The stylish yet compact body conveys its incredible potential to the rider's senses at a glance. And then, the power and usability of the new engine and body are immediately apparent the moment the electric starter is engaged, the motorcycle is put in gear, and the rider lets loose.
Please test ride the YZ450F and experience the evolution for yourself. We believe that you will quickly come to realise the amazing ease of riding the next level of performance from a 450 motocrosser.
