Big four-stroke single-cylinder dual-purpose motorcycles can be a compromise between road and dirt, but PETER MACKENZIE rides a thumper that covers all terrain better - by using two different dedicated sets of wheels.
Dual-purpose motorcycle makers occasionally supply some models with two sets of wheels, one pair each tailored for dirt and for road use.
In the best instances this likely means a decent-sized single cylinder bike with long travel suspension comes with a 21-inch front wheel and 18-inch rear with rim widths to suit mud-grasping dirt tyres.
As well, you can swap those knobblies for a couple of 17-inch Motard-rimmed wheels, with 120 (front) and 160 (rear) width rims to take the stickiest of road or racing rubber.
Fitting the different diameter wheels changes the bike's angle of attack, steepening up the forks and dropping the centre of mass.
Motard wheels on the asphalt sure make the bike 690 feel planted through corners, the tyre profiles providing quick and easy direction changes too.
With less than 140kg of bike, the rider can pick pretty much any line through a bend.
The sticky rubber makes for very confident braking, getting the best from the powerful Brembo units.
Hard to imagine a better bike for the twisties. It can lean right to the edge of the rear tyre tread, and that's well over.
With dirt wheels on, there's high ground clearance, and the larger wheels, especially on the front, better roll through troughs and across undulations.
The 18-inch rear makes for a generous footprint to find traction - and you need it with generous power on tap.
The big KTM can spit out giant, high-velocity rooster-tails of mud and stones if you open up the throttle.
When the 17-inch Motard wheels go on they sit the bike closer to the ground.
The centre of gravity drops and the stance brings the weight bias a little forward, plus steepens the fork rake for sharper handling.
It feels quite a different proposition to ride.
The well-rounded tyre profile adds to the ease of changing direction and presents a sticky contact patch across a wide range of angles.
KTM's 650cc single-cylinder four-stroke LC4 motor powers the Austrian company's 690 Enduro models and at the time of writing was the most powerful street-legal single of its type, with well over 60 horsepower on tap.
The bike employs the type of injection and management set-up developed by John Britten that uses computer-managed fuel injection with sensors for exhaust gas oxygen, manifold pressure, air temperature, throttle position, etc to optimise ignition and combustion.
This has been refined by Keihin and takes readings at the rate of hundreds a second.
That is the same system used, incidentally on the Triumph 675, another engine that seems to have notably better power and tractability than comparable mills.
Keihin's system exemplifies the benefits of fuel-injection, electronic throttle control and engine management, with myriad sensors co-ordinated to deliver perfect combustion.
The 690's got all the usual single low-range to mid-range grunt you'd expect, but where most big singles run out of breath at higher revs, this bike gets its second wind and accelerates harder again.
On a steep climb, the motor can deliver an extra punch that can kick rider and bike over an obstacle that would stall just about anything else.
On farm gully trails, the 690 snorts over rocks, washouts and through mud at any part of its rev range, even up absurdly steep climbs with what would normally be stop-you-dead-in-your-tracks obstacles.
The fuel injection has variable engine mapping via a rotary switch under the seat.
Set to standard the bike is grunty enough for most people, but it has a fast mode which advances engine timing.
Usefully, there's a detuned mode that limits output quite a bit, too.
That may sound strange, but if you're in 150mm of powder snow and negotiating icy spots, the snail mode is enough to keep you upright rather than sliding all uncontrollably and falling over.
There's also an emergency poor-grade-fuel mode (in case you can't feed the 690 it's normal 95-octane diet) to get you home on fuel rated anywhere down to the low 80s.
The advanced mode makes for gripping on tight - there's even more snap from the throttle.
With that sort of power on tap, you appreciate the bike's APTC slipper clutch.
In short, it's a kind of traction control that both keeps wheelspin under control, so you can open it up out of corners earlier for better exit speed plus it reduces wheel lock-up on downshifting.
Slick engineering means operation feels light and precise through the lever, via a braided hydraulic line.
It's got half the spring loading of a traditional clutch.
It makes the bike more forgiving and you can see why bike racers prefer slippers.
KTM aren't in the business of making at all average bikes, they like to engineer every part to do it's job well with the best and lightest material.
You don't feel the need to put after-market gear on one to lift power, reduce unsprung weight, or generally makes things work better: they've already designed or found the best bits and put them on their bikes.
Rims and hubs are trick and light, brakes are works of art to get maximum stopping power from the least mass of metal, hydraulic lines are all braided, the alloys of every metal part are probably the ones you'd choose if you wanted the best regardless of price, and suspension is certainly not from the cheap bin.
Inverted forks and rear single shock provide 225mm of precision-damped travel each end.
Both on and off road you appreciate its ability to soak away the rough stuff.
Over ploughed fields, the bike can traverse furrows at oblique angles without fuss, tracking straight and transmitting almost no shock to the rider.
The damping just smacks of quality engineering.
It has the power to tackle tricky, steep trails two-up and the high-set rear end helps keep the front wheel planted on steep climbs.
The chrome-moly trellis frame's a powder-coated exercise in lightness and rigidity, helping that suspension do it's job keeping the wheels tracking true.
Another frame notable is the petrol tank itself forms the structural member supporting the seat, rear guard, number plate and lights.
This gives lower, more rearward centre of mass than the normal tank location over the engine, plus eliminates several parts.
Seat itself is ultralight and easily removed for access.
It is extremely long and comfortable for both rider and passenger.
Where the petrol tank usually is, between the rider's knees, the KTM has its air filter box, which means less weight up high to chuck around, and no cold tank on your knees or other parts that might contact that area.
Watercooling keeps the motor finless and narrow, while the radiator's position deflects the wind away from knees.
The bike's instrumentation and lights are minimal and can be quickly removed.
Its analogue dial rev counter dominates the instrument unit which houses LCD temperature gauge, digital speedo with trip meters and warning lights.
Headlight is halogen and compact tail-light is LED.
There's an amazing amount of Austrian design cunning and engineering expertise in this KTM.
If you've a preference for radical dirt riding, KTM make an "R" version that's taller, with another 25mm of suspension both ends.
You wouldn't want to have short legs for that one, though.
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