ATK 605. .
WAS READY K)R A BIG-NO, MAKE THAT 5-/-G-SWAP.THEREI was no way this new ATK wasn't going to kick sideways.I As I sped down a bumpy two-track dirt road, a bike-eating I ditch suddenlyappeared, deep enough to squash both ends ofI any suspension, let alone an Open-class dual-purpose bike's. I Out ofoptions, 1 flew in, compressed and rebounded out. I Straight out, that is, nobuck, kick or twitch of any kind.
ATK's new 605 Thumper and its revolutionarysingle-sided frame had passed the extreme flex test. It is hard to comprehendhow a frame that connects the headset with only the lower-left swingarm pivotcould possibly be as rigid as an ordinary frame, but it is. And that's only thebeginning: Its design also allows a full 13.2 inches of rear-wheel travel, butwith a relatively low 36.5-inch seat height. Plus, it's 10 pounds lighter thanthe conventional frame it replaces.More oddities: The detachable lower frame rails and footpegs are divorced fromthe main frame and bolt on via the lower engine mounts; a skidplatesmooths the transition from a dead-end front downtube to the separate lowercradle, creating a tunnel for the left-side header pipe to pass through.
It is not at all strange for ATK to debut arevolutionary new concept on a motorcycle. Remember the company's A-trakchain-torque eliminator, from which the ATK name was derived? How about thecountershaft-mounted disc brake? Those ideas worked on paper, but real-worldconditions forced ATK back to more normal setups.
That should not be a problem with this new frame.The heart of the 605, its 598cc Rotax motor, is about as tried and tested asanything on two wheels. It's ancient by today's two-years-and-you're-outstandards, but it truly pulls its own weight-all 100 pounds of it. Feeding themotor is a 40mm Dell'Orto round-slide carburetor breathing through a K&N fabricair filter. The new airbox is actually an integral part of the all-aluminum rearsubframe.
A completely redesigned stainless-steel exhaustpipe gets the gasses out with less restriction and flows through a large-coremuffler capped off with SuperTrapp discs.
WP continues to produce suspension for ATK. The40mm inverted fork has full adjustment, this year with compression in one legand rebound in the other. As per usual ATK practice, the side-mounted WP shockis progressively valved and runs without a linkage.After years of borrowing bodywork from other brands, ATK went big this year andproduced its own sidepanels,giving the bike a distinct look.
The fuel tank is designed to call attention tothe new frame, and houses a claimed 3.6 gallons. The fenders and numberplate arestill sourced from Italian plastic maker UFO. Also on the thumbs-up list is thenew oversized front-brake rotor squeezed by a Brembo dual-piston caliper; muchimproved over last year, though still a notch off Honda's class-leading stopper.Depending on the model choice, starting is simple. With either the delicate pushof a button or the swift swing of a kick starter, the 605 will fire right up,even on a brisk, 30-degree Utah morning.
Though in the past Rotax motors have been finickyabout starting, the spot-on jetting of the ATK sorts this out. Warm-up isquick-no coolant to heat here.Small-handed riders will find the reach to the clutch lever excessive, buteveryone will appreciate the light pull and smooth engagement. The transmissiongives a solid feel and shifts respectably, though the throw may be a bit longfor those used to Japanese machinery. Spread of the wide-ratio five-speed willsuit everything from tight single-track rock climbing to cruising comfortably at65 mph on the interstate.
A wide powerband is one of the ATK's joys. Torqueis abundant, throttle response instant. It runs like a well-tuned Honda XR600,but with a much smoother bottom-end power spread. The slow-revving nature of themotor is deceiving, but ground speed tells the real story—the 605 simply ingestsoff-road miles. There's really no need to rev the motor, but the fact that youcan shows its versatility.Suspension settings are the same on all of ATK's
Thumpers. Because the dual-purpose model makes up95 percent of ATK big four-stroke sales, it comes as no surprise that thesettings cater to fireroads more than supercross-style double-jumps. If yourriding taxes the suspension, or the terrain gets nasty, the suspension hasenough adjustment to handle the situation. During our visit to ATK'sheadquarters in Bountiful, Utah, I raced a kick-start version with stocksuspension in a national hare & hound, and it worked admirably, rarelybottoming.
So, back to this half-a-frame concept. Riding thebike, you would never know that there is some weird, new-fangled frame beneathyou. Made up of large diameter, thin-walled tubing, it resembles half aperimeter-style frame, but seems amazingly rigid. The wrapped-steel swingarm,just like the one on the two-stroke LQ model, is much stronger than the ol"drectangular unit, and does its share to reduce flex, too.
The frame also carries the bulk of the engine's 3quarts of oil. This feels great on a cold day, but the heat can get to asit-down rider's left thigh in warmer conditions. ATK has, however, takenprecautions: The fuel tank has threaded inserts to allow the mounting of a heatshield.The electric-start 605 does not mask its claimed 280 pounds (260 for thekick-start model). On the plus side, the weight is well centered and low.Stability is great and we never experienced any headshake. Quick side-to-sideturns require an average amount of effort, on par with most big Thumpers.Sliding has never been easier, the low seat height allowing you to really get"into" the bike while hacking the back end out.
There is plenty of room to move about on the ATK.A long and spacious seat, and its relationship to the footpegs does not crampeven tall riders. Ground clearance is not an issue, with 13 inches before aframe rail touches down.Glitches? Some, and here is where we, and anyoneSI Buell Solo SaddleSI Buell Solo Saddle Doubles Seating Area. Finely Crafted. Uses Stock ScrewFitting. Meant For Solo Rider. #Sl $269.Corbin spending close to $8000 on a dirtbike, deserve to be critical—the finerpoints. We will always praise ATK's use of high-quality chains, handlebars,billet triple-clamps and hubs, and you get some of the best rims, spokes,sprockets, air filters and rotors on the market.
But it's small details that hurt the ATK: aflimsy aluminum plate that supposedly protects the chain guide, but bends whenpebbles hit it; footpegs that are plenty strong and functional, but become dirtscoops on contact with the ground; a flappy-flyer license-plate mount thatinterferes with the tire. Sure, dirt riders love to tinker with their bikes, butfor this many dollars, they shouldn't have to.Still, ATK has a great product here, in need of just a bit more polishing in afew areas. For the deep-pockets dual-purpose rider in search of a unique,innovative, exciting ride, ATK's new 605-strange frame and all-is up to speedand ready to rip. □
Source Cycle World 1996