HONDA The Power of Dreams

The first titanium fuel tank ever featured on a mass-production motorcycle made its debut in 2017 on the newly updated CRF450R. That same year, a titanium fuel tank also appeared on the totally revamped CBR1000RR SP/SP2. Studies reveal that titanium has roughly 60% the specific gravity of steel, which means that if a piece of sheet steel weighs 1kg, then a titanium sheet of the same size and thickness will weigh 600g. Little wonder that this rarified material is highly effective in weight reduction. Another prime characteristic of titanium is its resistance to corrosion and rust.

Because of this, highly expensive parts for racing machines are individually cut out of blocks of titanium using advanced milling equipment. Titanium is also used to make exhaust pipes and silencers, as well as the intake valves and connecting rods used in their engines. It is generally recognized that titanium contributes to higher performance by making it possible to reduce weight while simultaneously increasing structural strength.

Titanium compares favorably with aluminum and carbon fiber as a lightweight and appealing material. It’s also interesting how bikes that incorporate such attention-getting lightweight materials are sold, since it imparts a sense of excitement greater than any performance numbers can reveal.

Among its plans for the manufacture of attractive looking fuel tanks, Honda’s Kumamoto Factory had recently introduced two new types of tank: one is the flangeless tank, and the other the titanium tank. Let’s find out the reason why titanium was selected for use on its CRF450R motocross machine, the first model to be equipped with a mass-produced titanium tank.

Motoaki Takashima — Press molding department
“The press molding of titanium entailed a lot of trial and error. The way the titanium stretches when pressed differs depending on the orientation of the plate material. As a result, the titanium plate would stick to the press die, and we found that whereas some sections could be molded, other parts became crimped and torn because the plate wasn’t able to extend deeply enough into the die. We had to overcome numerous issues before we discovered these important characteristics about the metal.”

Chihara —
“When making the titanium plate, we roll the titanium material in a roller. However, the material has a tendency to stretch differently in the direction being rolled and the direction perpendicular to that (in-plane anisotropy). This increases difficulty in press molding it.”

Ryuji Masuda — Press molding simulation analysis
“Another factor that contributed to our difficulties was that, rather than using titanium plate, we had mainly used steel plate in our press molding simulations up till that point. The reason why we had to make so many press molding prototypes was that the theoretical simulation analysis technology was still not fully developed, and was not functioning very well.”

As there were no prior examples of press molding titanium plate into complex shapes such as a motorcycle tank, the team’s pioneering struggles continued.

Hirano —
“We tried to generate strength through design. Our goal was make a product that required no reinforcing members be added afterwards. As we were looking for both strength and lightness, the degree of difficulty in the press molding process was increased. However, this was an area where we could not compromise in our pursuit of performance.”

The CRF450R’s titanium tank is certainly lightweight. However, its designers also gave it a stamp of approval for having excellent corrosion resistance and safety aspects as a container for holding fuel.

In the early stages of the CBR1000RR’s development, the designers considered using an aluminum tank. However, in consideration of the processes involved, as well as the cost, weight, etc. of mass production, and encouraged by the Kumamoto Factory’s slogan of “Let’s do it!”, the designers decided to switch to a titanium tank, which despite being expensive as a material, was far lighter and offered greater product appeal.

Usa —
“We thought we could deliver up a more impressive version of the CBR1000RR, for which lightness is key. This is the great advantage of having a research laboratory and manufacturing plant in the same location, such as in Kumamoto. We were immediately able to talk face to face if any problems arose. We were thus able to find the direction we needed to move.”

Since they were coming up with new manufacturing methods, it was critical to have even more cooperation between departments than normal. So, how heavy is the resulting titanium tank?

Usa —
“It’s 1.7 kilograms, as opposed to 3 kilograms for the steel tank. For a component part like this that is mounted in such a high position, its lightness has a dramatic effect on maneuverability. It may be light, but we also took nothing for granted in regards to vibration.”

Before working on this story, I had encountered the CBR1000RR SP when shooting some photos for a magazine. I was amazed at how light it was when I pushed it to change its position. This model is also equipped with a lithium ion battery and other details that contribute to even lighter weight, so the titanium tank is not the only thing responsible for the CBR’s remarkable feeling of lightness. That said, its lightness and resulting enhancements to overall performance are essential to improving the sense of unified integration that is so important to achieving the highest levels of riding comfort and control.

The CBR1000RR is a model that pursues the ultimate in riding ease and comfort in a high-performance sports bike. Careful attention was also paid to its fuel tank design in order to enable the rider to move more freely.

Mizuta —
“For example, if you’re able to check out an actual bike at a dealership, please get up close to the tank, straddle it and lie on it. I think you’ll be able to appreciate the minute calculations involved in how the Fireblade’s tank has been shaped for riding.”

Usa —
“On the circuit, the rider usually lies on the tank when charging down the straights. At this time, if you rest the jaw of your helmet on the tank, the screen will come to just the right height. That is the kind of compactness we were aiming for.”

The history of mass-produced titanium fuel tanks begins with the CRF450R and CBR1000RR SP/SP2. Titanium’s lightness imparts greater maneuverability, which adds to any rider’s enjoyment.

This gives rise to the joy manifested in expressions such as “I never realized riding could be so much fun!” For me, such wonder represents a victory for hobby riders.

The challenges of motorcycle making will continue, and with it our victories will come closer to home. I pondered these thoughts as I bade farewell to Kumamoto.