The centered chain drive layout allows ample room for long travel suspension high performance suspension.
It was clear to Honda's engineers that a centered chain drive system was the solution because it allowed for the ideal length and placement of the A-arms. The first step was to move the drive sprocket from its traditional left-side position on the ATV. To do this the engineers designed an ingenious set of gears and shafts. First, a final-drive gear was attached to the end of the countershaft—where the drive sprocket is normally mounted. Then, the final-drive gear spins a final idle gear which, in turn, spins the final driven gear. (The idle gear is needed to maintain the counter-rotating direction of the drive sprocket.) The final driven gear is mounted to a shaft that extends inward toward the centerline of the ATV and on its end is mounted the drive sprocket. This amazingly compact gear unit locates the drive sprocket just 33mm to the left of the 700XX's centerline, giving the chain a straight run back to the rear driven sprocket. (The rear disc assembly sits an equal distance to the right of the centerline.) The driven sprocket is affixed to a compact receiver to which the equal-length rear wheel axle shafts are attached via constant velocity (CV) joints. So configured, the centered chain drive layout provides ample room for the location and placement of the desired A-arms.
Another benefit of the centered chain drive system is the ability to employ longer axle shafts. In the same manner that the up-and-down travel of long A-arms is circumscribed in a relatively small arc, so too is the effect with longer wheel axles. The positive benefit of minimal wheel axle travel is that the CV-joint angles are never extreme, thereby reducing power-robbing friction and the build-up of life-sapping heat.
A centered chain drive also contributes to the TRX700XX's mass centralization. When a rider initiates a turn, the ATV rotates around its roll axis—a fore-and-aft horizontal line drawn through the center of mass of the ATV and rider. Placing the major masses (engine, fuel, rider) closer to this roll axis results in an ATV that reacts more quickly and smoothly to control inputs at the handlebars. Centering the chain drive and moving the A-arm mounting points, CV joints and rear disc assembly as close as possible to the 700XX's centerline contribute to the application of the principle.
Honda’s centered chain drive system is a brilliant solution to an engineering problem that has puzzled designers of sport ATV IRS systems for years. By applying sound principles and some common sense in an effort to achieve an uncommon solution, we feel Honda, with their new patented centered chain drive system, has pioneered a very impressive invention for IRS equipped ATVs.
The frame of the TRX700XX is constructed of steel with a removable sub-frame. Independent double-wishbone front suspension uses steel A-arms and shock absorbers featuring two single-rate springs per side. This application of dual springs, a first for Honda, separates the function of each. Both the main spring and the short top spring (second spring) are single rate. Bottoming resistance is provided by the heavier main spring and the top spring adds compliance over small bumps. Together, they achieve what a progressive-rate single spring could have accomplished, but in a lighter, more compact package that takes full advantage of the 10.5 inches of useable suspension travel. Front preload is adjusted with screw-type adjusters. The A-arms are attached to aluminum steering knuckles, which in turn bolt up to aluminum hubs and 10-inch diameter aluminum wheels fitted with 21x7R-10 Dunlop radials.
The aforementioned independent double-wishbone rear suspension, made possible by the innovative centered chain drive system, features steel upper and aluminum lower A-arms. The upper and lower A-arms pivot on sealed needle bearings at the frame and support aluminum knuckles via oil-less bushings. The knuckles attach to steel hubs, and the 11-inch-diameter aluminum wheels sport 22x9R-11 Dunlop radials. The reason for steel hubs: greater resistance to side impacts and side loads. These steel hubs weigh less than an aluminum hub with the same strength characteristics. A non-adjustable rear sway bar attached to the frame and lower A-arms controls excessive roll without compromising the independent action of the IRS. Piggyback reservoir shocks provide 9.3 inches of fully usable travel and feature screw-type preload adjusters. Braking action is supplied by a hydraulic single piston squeezing a 200mm disc. The rear brake assembly is mounted on the rear sprocket receiver and is situated 33mm right of the 700XX's centerline—symmetrically opposed to the location of the sprocket/chain assembly to facilitate equal-length A-arms and drive shafts.
An interesting outgrowth of Honda's goal to fit the longest A-arms and axle shafts possible is the use of special 11-inch-diameter rear wheels (larger than competitive designs). The larger-diameter wheels allow the knuckles and hubs to reach farther into the wheel cavity, which effectively extends the A-arms and axle shafts to the perimeter of the 700XX's track width. To maintain strength and light weight, the thickness of the rear-wheel wall varies as it extends from the center plate to the outer ring of the wheel—another Honda ATV first. And here's another: the fitment of replaceable rim scrapers to remove mud and debris from rear wheels, a feature pioneered on Honda's popular Foreman and Rincon series.
