2004 Honda CBR600RR - Development

Mass Centralization

One of the central concepts that drove development of the CBR600RR and the RC211V is mass centralization; that is, concentrating the component masses as close to the motorcycle's center as possible. When a rider initiates a turn, the motorcycle rotates around its roll axis--an imaginary fore-and-aft horizontal line drawn through the center of mass of bike and rider--as it leans into the turn. Placing the major masses (engine, fuel, rider) closer to this roll axis results in a motorcycle that reacts more quickly and smoothly to control inputs at the handlebars. The concept of mass centralization has been a guiding principal at Honda for decades, but the application to the RR takes the concept to a whole new level.

Just as they did with the RC211V, Honda engineers looked at the CBR600RR as an organic whole for centralizing mass. Every change, every hard part was related and affected others. Part of the approach calls for lightening as many pieces as possible that are far from the center of mass. That gave rise to the RR's compact Line-Beam headlights, with their high-illumination three-piece reflectors-another Honda first for use on a production motorcycle; a lighter, more compact wheel hub design; slimline LED taillight; an analog/digital fully electronic instrument panel that's one of the lightest and slimmest ever mounted on a street bike; plus a host of other changes.

Really big dividends, though, come from moving the greatest masses closer to the motorcycle's center--the rider for instance. For example, a 160-lb. rider amounts to one-third of the total weight of the bike/rider equation when aboard CBR600RR. And compared to the F4i, the rider sits 70mm farther forward on the RR.

The crucial element, and what made that radical repositioning possible, comes from another idea lifted directly from the RC211V: the fuel tank, and its placement. A plastic cover gives the RR "fuel tank" a traditional look, but the front half covers the 15-liter airbox (1.0 liter larger than the F4i's), and the back half covers the tank itself. Only the top one-third of the fuel tank is visible above the frame rails, with the remainder extending down almost to the top of the crankcases. The Unit Pro-Link rear suspension (which does not use a traditional upper frame mount for the shock) helps make room for the fuel tank's lower placement (more on this later). A more compact shape than the F4i's conventional tank permits the RR to have the same 4.8-gal. capacity, while weighing 1.0kg less. Compared to traditional designs, the RR's fuel placement contributes to centralizing mass via its location, and by allowing the rider to be placed farther forward. In addition, the tank's placement ensures the RR's handling won't be affected by changing fuel loads--another trait it shares with the RC211V.

An All New Engine

The CBR600RR's all-new 599cc liquid-cooled inline four-cylinder engine also contributes greatly to mass centralization. One of the major design goals for the engine was to make it more compact. By shortening its length, it would be possible to move the engine--and the rider--closer to the steering head, and thus closer to the machine's center of mass.

To accomplish this, engineers rejected the conventional configuration that places the crankshaft, mainshaft and countershaft all along the crankcase split line. Such a design makes for easy assembly, but limits the amount the engine can be shortened. Instead, they placed the mainshaft 48.4mm above the cases' centerline. This allowed moving the countershaft closer to the crankshaft in a triangulated layout. This, in turn, also assisted in moving the swingarm pivot 30mm closer to the crankshaft. Engineers also rotated the engine's exhaust ports 30 degrees downward compared to the F4i's ports. Doing so allowed the headers to curve more closely to the engine, which enabled engineers to move the engine 9mm farther forward.

Shortening the engine had yet another benefit. It allowed lengthening the swingarm to 573mm (43mm longer than the F4i's), making the RR's the longest in the class. A longer swingarm not only shifts the weight bias forward, it also makes for more progressive suspension action by reducing the angle the swingarm rotates for a given suspension movement.

The CBR600RR's awesome 599cc liquid-cooled inline four-cylinder is an all-new powerplant. It does share the same bore and stroke dimensions (67mm x 42.5mm) as the F4i's engine, but that was decided only after extensive testing with other cylinder dimensions. Honda's engineers found the F4i's displacement numbers would also be ideal for the RR's performance goals.

One of those goals was class-leading horsepower, and engineers succeeded beyond most riders' imaginations. The CBR600RR's engine makes peak rear wheel horsepower at 12,500 rpm, compared to the F4i's peak at 12,000 rpm. For racing, the RR also provides far more overrev capacity, with a 15,000-rpm redline that allows riders to wind past the engine's power peak when it's not possible to shift, or when doing so would slow them down, an important racing benefit.

Such extremely high engine-speeds create impossibly short intake/exhaust intervals that can push conventional fuel-delivery systems past their limits. To solve that problem, engineers applied a new Honda technology lifted directly from the dominating RC211V: Programmed Dual Stage Fuel Injection (PGM-DSFI). DSFI combines the RR's four Denso 40mm throttle bodies with four more injectors located in the top of the airbox. At engine speeds below 5500 rpm, only the throttle body injectors work. Above that rpm the airbox injectors also come into play. The injectors feature 12 holes that deliver a finely atomized air/fuel mixture. A 32-bit ECU operates with far more speed and accuracy than the F4i's 16-bit ECU, and provides optimum performance throughout the entire rpm range. (See Programmed Dual Stage Fuel Injection technical feature for more details.)

A Dual-Stage Air Induction ram-air system feeds dense, cool air to the airbox, but now via larger inner/outer ducts. Extensive testing in the wind tunnel and on the race track showed the larger ducts resulted in a slight increase in steering effort. To counteract that trait, the outer ducts have holes punched through them, an idea Honda successfully tried years before on its Grand Prix road racers. As a result, the RR makes high-speed transitions with ease and confidence.

The RR's MotoGP-style engine redline also required engineers to pare down reciprocating weight. To that end, the RR's forged slipper pistons are even lighter than the F4i's pistons, 131g vs. 145g, for a 14g savings each. Shorter, smaller-diameter tool-steel piston pins save another 8g (36g vs. 44g). And new carburised connecting rods feature a lighter nutless design Honda pioneered with the 1998 Super Hawk. The new rods save 12g--232g vs. 244g. That amounts to 34g savings per cylinder, or 136g (4.8 ounces) of reciprocating weight. Overall, the RR's engine weighs 0.7kg less than the F4i's.

Intake valve diameter is larger than the F4i's, 27.5mm compared to 26.5mm. And both intake and exhaust valves are closed by nested pairs of valve springs. Two lighter springs tend to follow cam profiles better than one heavier one, they can provide more spring pressure for better sealing, and the friction between them damps the surge that can cause the bucket tappets to lose contact with the cam lobe. A new, dual-pivot tensioner keeps the cam chain from whipping at high rpm. A short secondary guide overlaps the conventional main guide to provide additional pressure closer to the cam sprocket without excessive friction.

Another design goal for the RR's engine was to make it more compact than the F4i's to increase cornering clearance. To do so, engineers moved the crankshaft-mounted starter gear from its traditional position on the left-hand side, behind the ACG, to the right-hand side. That allowed them to move the ACG farther inboard, reducing the distance from the engine's centerline to the outside of the ACG's cover by 21.5mm. Those changes, plus reshaped covers for the ACG and clutch, account for a 3 degree increase in bank angle on both sides of the motorcycle. A center-up exhaust system--again, inspired by the RC211V--also contributes to increased cornering clearance, and creates no aerodynamic drag.

Chassis

Honda's CBR600s have always had a reputation for exemplary handling, a reputation engineers wanted to enhance with the all-new CBR600RR. It was a daunting task, but what better place from which to draw inspiration than the MotoGP champion, Honda's RC211V?

The CBR600RR's frame, for example, makes use of the mass centralization ideas proven so well on the RC211V, starting with placing the fuel tank low in the aluminum frame. That facilitated positioning the engine and rider farther forward, pushing all three closer to the center of mass than with the F4i's frame.

And the RR took yet another chapter from the RC211V's winning play book, with its Unit Pro-Link rear suspension--technology never before seen on a street bike. Unit Pro-Link attaches the top of the shock absorber to the heavily braced aluminum swingarm, rather than to an upper-rear frame crossmember. As the rear wheel passes over a bump, the shock is compressed at the bottom by a set of links (see Unit Pro-Link technical feature for more details).

A host of benefits cascade from this simple, elegant idea. It facilitates placing the fuel tank low, because there's no crossmember locating the top of the shock. Furthermore, with Unit Pro-Link, the shock absorber's loads don't get fed into the frame's downtube structure, which allows the engineers unprecedented freedom in frame design, so they can tune the frame for very specific characteristics.

Honda's new aluminum frame technology

Yet there's still another technological leap Honda's engineers needed to make to take full advantage of their new design freedom. Honda has long pioneered the use of all-aluminum frames for street bikes and off-road motorcycles. Each use requires different construction and tuning, but they often use a collection of castings, forgings, pressings or extrusions. Now, though, after years of research and development, Honda has made a huge leap forward in manufacturing aluminum frames with the advent of Hollow Fine Die-Cast technology. What this means is designers have a unique new freedom to create freely formed, hollow-section die-cast frame members, but with much thinner walls than ever before. With previous conventional Fine Die-Cast techniques, the thinnest walls possible had been 3.5mm. With Honda's new Hollow Fine Die-Cast technique, an unprecedented 2.5mm wall thickness is now possible.

What made the procedure possible is ceramic coating of the sand-formed interior mold sections (sunanakago in Japanese casting terms). Before, the sand-formed sections would crumble under the heat and pressure of the die-cast aluminum. The ceramic coating keeps the sunanakago intact, permitting the casting of such thin-wall structures.

The CBR600RR's frame consists of five pieces that use this breakthrough technology: the steering head, both downtube structures, and both swingarm pivot plates. Using Hollow Fine Die-Cast techniques, engineers have even greater latitude to tune frame members to specific rigidities to enhance handling. What's more, Hollow Fine Die-Casting saves time on the production line by virtue of more accurately cast components.

The same technology is used to create the RR's subframe. The subframe's inner walls are incredibly intricate, with a maze of strengthening webs, all precisely placed. In addition, the Hollow Fine Die-Cast technique allows creation of a custom-fit for the center-up exhaust, reducing the expense and complication of trying to accomplish the same task with conventional methods.

The most advanced sport bike Honda has ever produced

You can trace an unbroken line directly from the original CBR600 to today's all-new CBR600RR. The RR carries on the same tradition of phenomenal performance--in fact, the highest levels of performance ever available from a middleweight motorcycle. But Honda's CBR600RR takes the concept even further than the CBR600 family ever did. The original CBR was the purest expression possible of what was then-current technology in inline-four engines, steel frames and single-shock Pro-Link rear suspension.

The 2003 CBR600RR pushes back current technological boundaries. That's because you can also trace a line directly from the RR to Honda's breakthrough RC211V. That lineage is what makes the CBR600RR a watershed in motorcycling. It takes the latest, world-championship-winning technology, and applies it in real time to a motorcycle that's available now--not next year, or the year after that. It's also what makes the CBR600RR the most advanced sport bike Honda has ever produced.

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