Difference between revisions of "ATK 605"

[[ATK]]'s new 605 Thumper and its revolutionary single-sided frame had passed the extreme flex test. It is hard to comprehend how a frame that connects the headset with only the lower-left [[swingarm]] pivot could possibly be as rigid as an ordinary frame, but it is. And that's only the beginning: Its design also allows a full 13.2 inches of rear-wheel travel, but with a relatively low 36.5-inch seat height. Plus, it's 10 pounds lighter than the conventional frame it replaces.

[[ATK]]'s new 605 Thumper and its revolutionary single-sided frame had passed the extreme flex test. It is hard to comprehend how a frame that connects the headset with only the lower-left [[swingarm]] pivot could possibly be as rigid as an ordinary frame, but it is. And that's only the beginning: Its design also allows a full 13.2 inches of rear-wheel travel, but with a relatively low 36.5-inch seat height. Plus, it's 10 pounds lighter than the conventional frame it replaces.

More oddities: The detachable lower frame rails and footpegs are divorced from the main frame and bolt on via the lower engine mounts; a skidplate smooths the transition from a dead-end front downtube to the separate lower cradle, creating a tunnel for the left-side header pipe to pass through.

More oddities: The detachable lower frame rails and footpegs are divorced from the main frame and bolt on via the lower engine mounts; a skidplate smooths the transition from a dead-end front downtube to the separate lower cradle, creating a tunnel for the left-side header pipe to pass through.

Though in the past Rotax motors have been finicky about starting, the spot-on jetting of the ATK sorts this out. Warm-up is quick-no coolant to heat here.

Though in the past Rotax motors have been finicky about starting, the spot-on jetting of the ATK sorts this out. Warm-up is quick-no coolant to heat here.

Small-handed riders will find the reach to the clutch lever excessive, but everyone will appreciate the light pull and smooth engagement. The transmission gives a solid feel and shifts respectably, though the throw may be a bit long for those used to Japanese machinery. Spread of the wide-ratio five-speed will suit everything from tight single-track rock climbing to cruising comfortably at 65 mph on the interstate.

Small-handed riders will find the reach to the clutch lever excessive, but everyone will appreciate the light pull and smooth engagement. The transmission gives a solid feel and shifts respectably, though the throw may be a bit long for those used to Japanese machinery. Spread of the wide-ratio five-speed will suit everything from tight single-track rock climbing to cruising comfortably at 65 mph on the interstate.

A wide powerband is one of the ATK's joys. Torque is 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 the motor is deceiving, but ground speed tells the real story—the 605 simply ingests off-road miles. There's really no need to rev the motor, but the fact that you can shows its versatility.

A wide powerband is one of the ATK's joys. Torque is 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 the motor is deceiving, but ground speed tells the real story—the 605 simply ingests off-road miles. There's really no need to rev the motor, but the fact that you can shows its versatility.

So, back to this half-a-frame concept. Riding the bike, you would never know that there is some weird, new-fangled frame beneath you. Made up of large diameter, thin-walled tubing, it resembles half a perimeter-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"d rectangular unit, and does its share to reduce flex, too.

So, back to this half-a-frame concept. Riding the bike, you would never know that there is some weird, new-fangled frame beneath you. Made up of large diameter, thin-walled tubing, it resembles half a perimeter-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"d rectangular unit, and does its share to reduce flex, too.

The frame also carries the bulk of the engine's 3 quarts of oil. This feels great on a cold day, but the heat can get to a sit-down rider's left thigh in warmer conditions. ATK has, however, taken precautions: The fuel tank has threaded inserts to allow the mounting of a heat shield.

The frame also carries the bulk of the engine's 3 quarts of oil. This feels great on a cold day, but the heat can get to a sit-down rider's left thigh in warmer conditions. ATK has, however, taken precautions: The fuel tank has threaded inserts to allow the mounting of a heat shield.

The electric-start 605 does not mask its claimed 280 pounds (260 for the kick-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-side turns 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.

The electric-start 605 does not mask its claimed 280 pounds (260 for the kick-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-side turns 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.

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==1992 ATK 605==

==1992 ATK 605==