Cycle News - Archive Issues - 1990's

TEST (left) Dirt track veteran Terry Poovey ralls the ATK600MR prototype through a turn. The finicky Poovey gave the machine a favorable rating despite, and no surprlsea here, his feeling thet It needed more power. Photos by Greg Mitchell and Dan Mahony liders, stand up and take notice. The 1998 ATK 600MR dirt tracker i for real. It is not the third coming of the faux flat track street bike which sports nothing more than dirt track styling and the name of a historical race track or the model designation letters of a legendary line of dominant, purposebuilt dirt track V-twins (remember those?). Oh no. What we have here, friends, is an answer to the impassioned pleas of the steel-shoe set for an honestto-God, rip-snortin' circle burner that can be purchased, ready to go, right off the showroom floor. All say hallelujah! The story of its existence began when ATK engineers relished the idea of building an all-purpose motorcycle not so much a dirt track-only motorcycle, but more a BSA Gold Star for the '90s. The Bountiful, Utah-based manufacturer already had the perfect powerplant for such a machine in the same venerable Rotax four-stroke single that powers the ATK 605CC and DS models. It's no secret that the Austrian-built thumper has already proven itself successful around the world as a competent motocross, dirt track and singles road racing engine. Harnessed in the proper chassis, ATK figured, the reliable and potent mill should be just what the doctor ordered. But whereas the company had plenty of experience developing its Iinkageless rear suspension off-road frames, ATK realized, to its credit, that building a workable dirt track chassis would require the help of someone more familiar with the science of backing, rather than railing, a motorcycle through a turn. In early 1996, the company struck a development deal With the Michiganbased Total Control Racing team, the well-financed privateer squad for S "Although this frame is constructed similarly, we didn't just pull one of our frames off the line to build this bike," says Phil Walker, chief engineer in research and design at ATK. "The geometry, the gusseting, all of it is designed with dirt track in mind." The chassis is still based on ATK' s "modHied perimeter" theory, which features a single spar on the left side of the steering head and a single front down tube that bolts to the front of the (Left) Former engine. The engine itself is cradled by the frame, yet ATK elected not to tie the down tube and the engine cradle together, bu t rather to utilize the engine as a stressed member of the chassis in the interest of saving weight while not sacrificing rigidity. As Walker suggests, the MR differs from its off-road and dual sport siblings in t!Je geometry department. After consulting with TCR, the decision was made to build the prototype chassis with a steeper head angle, 25 degrees instead of the 27 found on the off-road bikes. Wheelbase is also significantly shorter, as the MR measures out to 57 inches, two inches less than the 59 inches found on the rest of the four-stroke line. • Suspension components are different as well. ATK shortened up, changed the internals and mounted one of its side-link WP rear shocks to the linkageless rear swingarm. Rear suspension travel is now six inches. Up front a pair of WP Roma dirt track forks take up residence in the triple clamps, providing seven inches of movement. The rest of the motorcycle is typical ATK and, as such, uses many of the same high-quality components found on the rest of the model lineup. That (Right) The machine's confidenceInspiring handling allowed even our amateur testers to run It Into the turns hard. The motorcycle Is extremely forgiving and an excellent learning tool. Rookie of the Year Paul Morgan III commented thet the bike needed a little more compression damping to keep It from squatting when accele~ng off of the turns. Morglin praised the MR's brakes and front suspension. whom veteran racers Kevin Atherton and Will Davis finished second and third in the AMA Grand National Championship Series by the end of that year. TCR received its first prototype in November of '96, and after spinning countless laps with both Davis and Atherton aboard, suggested the necessary changes to ATK. The motorcycle you see here is the end resuJt. WHAT'S THE DEAL? Before you go running down to your local ATK dealer and purchase a 605CC for conversion into a dirt tracker, you'd better listen up. Though the 600MR aesthetically mirrors the company's offroad line, the chassis is specific to the requirements placed upon it by the rigors of dirt track racing.

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