The engine bucks below 3,700 rpm, especially under acceleration, a characteristic inherent to high displacement - high compression - high performance singles. This behaviour is a result of the significant variations in crankshaft rotational speed, as the engine goes through the four cycles. Here is what happens: Maximum crank rotational speed happens at the end of the power stroke. The rotating masse (crank, clutch, tranny shafts, balance shaft, alternator-starter) then loses energy and speed as it goes through the exhaust, intake and compression strokes, before being kicked back up again at the next power stroke. At low rpm, this variation produces the snatching effect you feel on big singles as the crank accelerates and slows down again, taking up and releasing any looseness in the drivetrain.

Ergos are sit-up sporting, good for weaving through traffic, sliding around in parking lots or shaming more powerful bikes on the track.

There are two cures to this phenomenon, other than adding more pistons: increase rotating mass to store some of the energy from the combustion stroke, then use it up over the next three strokes, or pushing the engine higher up in the rpm so that the variations happens too quickly for you to feel them. KTM took the first route by adding rotating mass, happily not enough to soften the engine to the point of dullness or decrease the amount of energy available for moving the machine. As for the rpm, the rider must keep the mill on the boil and happy. Go past 4,000rpm and the engine hums and pulls like crazy.

Engine vibrations are another story, as all is relatively calm below 5,500 rpm, where you start to feel the big single vibrating through the pegs and the grips. But you are presumably busy paying attention to your riding at the time, and this is a high performance machine, one where KTM decided to not strangle the engine. So live with it or get a calmer bike.

The gearbox must be sturdy enough to take a beating from the big explosions, but still feels light and easy to operate; and it is both. I missed a few clutch-less upshifts, but judging from the suspension too-hard settings I found on it, I suspect the bike had been mistreated by previous "high performance" riders.

The Duke uses a typical steel trellis frame, mostly hidden by Austrian-slick bodywork.