Power is channeled through a five-speed gearbox with reverse and is transmitted to the rear wheels via an ingenious centered chain drive system. Conceived with the goal of maximizing the architecture of the long A-armed, double-wishbone independent rear suspension, a row of final gears located after the countershaft positions the drive sprocket almost dead center of the machine. This produces numerous benefits, including the use of longer A-arms and axle shafts. Longer A-arms minimize wheel camber changes as the suspension travels up and down—a handling benefit—and longer axle shafts mean that CV joints operate at less extreme angles, benefiting power efficiency and long-term durability. A further benefit of the design is simplified maintenance.
Top speed in reverse gear is controlled by monitoring both actual speed and crankshaft speed. When vehicle speed is no less than 12 mph and the engine speed is no less than 3050 rpm (equivalent to 12 mph), fuel delivery to the injector is restricted. Another noteworthy aspect of the gearbox is the engine reduction ratio at the drive sprocket: 1.087:1. This was done to permit the fitment of a smaller-diameter rear sprocket, which in turn allows the sprocket receiver assembly to be located lower on the frame. In addition to lowering the center of gravity, the smaller diameter of the sprocket and its assembly also improve ground clearance.
If you ask us Honda's Centered Chain Drive System is pure genious.
Is this not the most protected rear sprocket and brake mechanism you've ever seen?
Before we move on to the Chassis and Suspension we need to talk more about Honda’s centered chain drive system, which is an outstanding design as far as we’re concerned. It was designed with the goal of providing optimum power delivery without sacrificing handling. All the while it needed to do this without adding too much weight to the machine. At the end of the day Honda impressively solved a number of issues typically associated with an Independent Rear Suspension (IRS) machine. We feel Honda’s engineers rose to the occasion and delivered the best design since their eccentric chain adjustment system in the eighties, which is now found on most ATVs.
A compact, centered shaft-drive system similar to the IRS-equipped TRX680FA Rincon could allow the use of equal-length A-arm rear suspension, but it was ruled out for three reasons. First, a shaft drive and its corresponding differential are heavier than a simple sprocket-and-chain drive system and the IRS-spec'd TRX700XX needed to be lean and nimble. Next, shaft drive is not as efficient as chain drive when transmitting power, a decided negative for a high-performance platform.
Clearly chain drive was the solution. The problem: traditional engine side-mounting of the countershaft sprocket meant that the location of the rear sprocket and chain would intrude into the travel space occupied by the A-arms.
This shot really shows off the whopping 10.2 inches of ground clearance.
Double-wishbone suspension is ideal in an IRS setup because it offers longitudinal and lateral strength and rigidity, allows for smooth shock absorber action and provides optimal control of rear wheel travel at both low and high speeds. By making the upper and lower A-arms as long as possible, camber changes are kept to a minimum as the suspension arcs through its travel. This translates to a more consistent tire contact patch when traction is at a premium. The best way to achieve this is to attach the A-arms as close to the center-point of the vehicle as possible. But when a large sprocket and chain occupy the space needed for the movement of the A-arms, compromises must be made. If the A-arms are shortened so that their frame mounting points are outside of the chain line, significant camber changes occur when the suspension is fully compressed or extended, minimizing and moving the tire contact area. Another approach is to lower and/or tilt the inboard frame mounts of the lower A-arms (reducing ground clearance) and utilize a single-beam I-arm as the upper locating link. But an I-arm is less able to resist the twisting and flexing forces exerted on it; indeed these forces can be transmitted to the rear shock as well, causing it to bind. A more radical strategy employed by some competitive machines involves attaching the upper I-arm at a point farther back and lower on the frame. “Tucking the tail” of the rear suspension in this manner results in a mechanical control angle (the plane of the rear control arm mounting points relative to the plane of the drive-and-driven sprockets) as severe as 15 degrees—5 degrees is optimal—which effectively shortens the wheelbase when the suspension is fully extended and lengthens it when the suspension is fully compressed. The result is a fore-and-aft pitching over undulating terrain that can significantly impede predictable handling.
