Quad Bikes World

2008 Sportrax TRX700XX: Extreme engine performance, combined with a chassis that lets you put all that power to use. The stunning new TRX700XX brings the stable, confident handling that Honda ATVs are famous for to the big-bore IRS class. The engine is a high-tech marvel, boasting 686 cc of fuel-injected, liquid-cooled power and torque. And the chassis is even more advanced, with innovative features such as a central chain drive to the rear wheels that allows perfectly symmetrical rear A-arms and driveshafts, plus numerous other benefits. The result? Reduced wheel scrub, improved rigidity, and a much more planted feel in all conditions. One ride, and you'll feel the difference. Its electric-start, fuel-injected 686cc four-stroke engine traces its heritage to the Baja-dominating XR650R and delivers class-leading power. Just as significant, the drivetrain and suspension of the TRX700XX are state-of-the-art and then some. Specifically, Honda has engineered a brilliant centered chain drive system that permits the use of fully Independent Rear Suspension (IRS) with more advantages than traditional IRS designs.

The essential of the 700XX is its 686cc dry-sump, liquid-cooled SOHC four-valve single-cylinder four-stroke engine. With a bore and stroke of 102mm x 84mm, it boasts the largest diameter single-cylinder that Honda has ever mass-produced. Although it is infused with the heart of the potent XR650R mill, the 700XX engine has been purpose-designed and built for the rigors of ATV duty. Given the higher weight of ATVs (compared to off-road motorcycles), torque—and lots of it—was a priority. A longer (plus 2.0mm) stroke and slightly larger (plus 1.4mm) bore accomplish this. But in keeping with Honda’s philosophy of mass-centralization and a low Cg (center of gravity) to achieve optimal handling, engineers concluded that a taller cylinder and engine would not do. So they shortened the overall height of the engine by creating a longer-throw crankpin and a correspondingly shorter, carburized connecting rod to shorten cylinder height. The connecting rod is affixed to a ball-bearing crankshaft. Smooth, all-day riding comfort was assured with the fitment of a gear-driven counterbalancer to counterbalance engine vibration.

Like Honda’s renowned CRF motocrossers, the XX piston features a slipper skirt design and it strokes through a centrifugally forged, 3.5mm-thick steel sleeve. A forged piston was used to handle the increased mechanical and thermal loads, and it also benefits from an underside shower of cooling oil shot from a jet that protrudes into the center of the engine case. Compression is 10:1 and the high-tech slug is fitted with a larger 24mm piston pin. The combustion chamber utilizes a pentroof shape and is fired by a single, centered spark plug.

The engine inhales through a foam air filter fitted in a 7.6-liter airbox. Intake valve size is 1mm smaller than those used in the XR (36 vs 37) for better low-rpm flow—and therefore torque—while the exhaust valve diameter remains unchanged at 32mm. The Programmed Fuel Injection (PGM-FI) system draws fuel from a 3.6-gallon blow-molded, multi-layer fuel tank and delivers it via a single Denso injector through a 44mm throttle body. A Keihin Engine Control Module (ECM) manages both the fuel injection and the transistorized ignition. The engine exhales through a single long-tube header tuned for excellent low-end and mid-range torque without sacrificing top-end power. Gases are expelled through a muffler constructed of 128-grade stainless steel.

Several improvements are made to the engine to simplify its operation and enhance durability. An automatic decompression system is activated whenever the electric starter is engaged. The starter-motor housing is incorporated into the engine crankcase casting and a disc-type torque limiter minimizes shock to the starter mechanism.

The frame of the TRX700XX is constructed of steel with a removable sub-frame; each is extremely durable and strong. Independent double-wishbone front suspension uses steel A-arms and premium 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 TRX700XX shows off its high-performance capabilities with aggressive sports styling. A polyethylene push bar, polypropylene rear A-arm protectors and high-impact urethane frame and engine-case protectors are tough, lightweight and replaceable. A cowl-inte-grated headlight with dual 30-watt bulbs provides superb lighting and a highly visible LED brakelight is the most common view competitive riders will have of the new TRX700XX.

The TRX700XX redefines the Sport category of ATVs with a whole new level of confidence, comfort and high performance. With double-wishbone Independent Rear Suspension (IRS), a unique centered chain drive system, and a fuel-injected 686cc engine making monster torque, the TRX700XX is Best of the Best Sport ATV.