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.
The heart of the 605, its 598cc Rotax motor, is about as tried and tested as
anything on two wheels. It's ancient by today's two-years-and-you're-out
standards, but it truly pulls its own weight-all 100 pounds of it. Feeding
the motor is a 40mm Dell'Orto round-slide carburetor breathing through a K&N
fabric air filter. The new airbox is actually an integral part of the
all-aluminum rear subframe.
A completely redesigned stainless-steel exhaust pipe gets the gasses out
with less restriction and flows through a large-core muffler capped off with
SuperTrapp discs.
WP continues to produce suspension for ATK. The 40mm inverted fork has full
adjustment, this year with compression in one leg and rebound in the other.
As per usual ATK practice, the side-mounted WP shock is progressively valved
and runs without a linkage. After years of borrowing bodywork from other
brands, ATK went big this year and produced its own sidepanels, giving the
bike a distinct look.
The fuel tank is designed to call attention to the new frame, and houses a
claimed 3.6 gallons. The fenders and numberplate are still sourced from
Italian plastic maker UFO. Also on the thumbs-up list is the new oversized
front-brake rotor squeezed by a Brembo dual-piston caliper; much improved
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
push of 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 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.
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. Suspension settings are the same on all of
ATK's
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 old 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 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.
There is plenty of room to move about on the ATK. A long and spacious seat,
and its relationship to the footpegs does not cramp even tall riders. Ground
clearance is not an issue, with 13 inches before a frame rail touches down.
But it's small details that hurt the ATK: a flimsy aluminum plate that
supposedly protects the chain guide, but bends when pebbles hit it; footpegs
that are plenty strong and functional, but become dirt scoops on contact
with the ground; a flappy-flyer license-plate mount that interferes with the
tire. Sure, dirt riders love to tinker with their bikes, but for this many
dollars, they shouldn't have to. Still, ATK has a great product here, in
need of just a bit more polishing in a few 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 speed and ready to rip.