There's a reason why big enduro bikes - and, by extension, supermotards - have thumping great single-cylinder engines. Off-road riding - and inner-city hooliganising! - are all about huge gobs of torque, delivered without hesitation across a wide mid-range to cope with rapidly changing, unpredictable conditions.

So I could never understand what possessed Aprilia head Ivano Beggio to push ahead with a range of enduro and motard machines powered by a high-revving, short-stroke V-twin until I rode one - an SXV 550 supermotard. The experience was unforgettable.

Just standing there, the SXV is different. Its styling is so extreme it's almost a caricature of an enduro bike, yet it all hangs together to give it a seriously purposeful air. All its parts are tough and capable but there's nothing crude in the execution. The detail work is breathtaking, the finish superb. As much as the KTM RC8 is a superbike built by an off-road company, so the Aprilia SXV is a motard built by a factory specialising in GP bikes.

Then you thumb the start button - there's no electric foot - and all pretence of finesse vanishes. There's an automatic decompressor on the front exhaust cam so the engine starts on the rear cylinder only, with enough mechanical clatter for a foundry as all the components try to catch up with each other. Even when it's hot the decompressor mechanism rattles, the camchains whizz round and the clutch basket chatters like an Italian housewife.

But drop it into gear, pull away (gently, this thing will wheelie at half throttle in first) and all is revealed. As soon the inevitable power-thudding is dealt with and the revs rise above 3500 on the tiny digital readout in the bottom right hand corner of the liquid crystal display LCD (I didn't know it was there until the second day) the power delivery becomes smooth, manageable, perfectly modulated - in a word, unintimidating, even though throttle response is cobra-quick.

The bike begins to vibrate a little unpleasantly above 5500rpm so you tend to change gears at about 7000, moving up through the crisp, slightly notchy, five-speed box to cruise at about 110km/h. But the factory bumph speaks glibly of five-figure revs and 160km/h top speed in street trim so you stifle mechanical empathy and give it a handful - and all hell breaks loose.

The revs rise from 7000 to 10 000 so fast the rev counter becomes a blur - even the big digital speedometer changes too fast to read - the 'bars shake as the front end gets light (in top gear!) and there seems to be as much shake, rattle and roll coming from the running gear as the engine while the Aprilia tries to institute its own coup d'etat.

So you let out a very rude word, snap the throttle shut, the front end dives and wiggles bad-temperedly under weight transfer and you realise that the way to ride this bike is with smooth, firm movements of throttle, brakes and handlebars - it doesn't like tentative inputs and it'll bite if you get rough with it.

52.2kW at 10 900 RPM

Ivano Beggio's baby is an astonishing engine. Where other V-twins are signing off this one is just getting into its stride. High-performance V-twins combine torque and top-end like no other engines (ask anybody who's raced against a Ducati) and the SXV's short (55mm) stroke and precise fuel-injection give it phenomenal output, albeit at the expense of a flat, nasty intake roar and intrusive vibration.

The factory quotes 52.2kW at 10 900rpm and 69.3Nm at 8700 - and I see no reason to doubt the numbers. On the only top-end run I was happy with the bike went up to an indicated 150km/h very quickly and recorded a true 158km/h at 10 600 not very much later - with me sitting bolt upright, which is probably why every ripple in the tar seemed to unsettle the front wheel.

The Aprilia didn't feel at ease at high speed so I curtailed the quest for terminal velocity and went off to my favourite twisties, where I soon confirmed that the SXV's ground clearance is limited only by its tyres, its turn-in quick to the point of insanity - and quicker still with the astonishing FTE radial-mount front brake on, thanks to the supple Marzocchi front suspension.

But it's also reassuringly stable in mid-corner once the suspension is nicely loaded - not only will it dive in under your friends' superbikes, it'll also outdrag them coming out up to about 150km/h - and around town it'll eat them for breakfast thanks to its lightning responses. But those same lightning responses make it an uncomfortable commuter. It'll slip through any gap in the traffic but doesn't like small throttle openings.

TOP OF THE CLASS

Truth to tell, it's uncomfortable all the time. The seat is 918mm high and uncompromisingly hard, straight and narrow with rounded edges - it's like sitting on a fence pole - but supermotards are not about comfort. They're about inner-city hooliganising, about stretching agility to the point of instability and, above all else, about insane acceleration - and in those the Aprilia SXV is right at the top of its class. Beggio was right after all.

Price: R81 995.

Bike from Eurobike, Cape Town.

SPECIFICATIONS

ENGINE

Cylinders: Two.

Capacity: 549cc.

Bore x stroke: 80 x 55mm.

Compression ratio: 12.0:1.

Valvegear: SOHC with four overhead valves per cylinder.

Power: 52.2kW at 10 900rpm.

Torque: 69.3Nm at 8700.

Induction:Electronic fuel-injection with two 40mm throttle bodies.

Ignition: Digital electronic.

Starting: Electric.

TRANSMISSION

Clutch: Cable-operated multiplate wet clutch.

Transmission: Five-speed constant-mesh gearbox with final drive by chain.

SUSPENSION

Front: 48mm Marzocchi inverted cartridge forks adjustable for preload, compression and rebound damping.

Rear: Rising-rate linkage with remote-reservoir Sachs gas-filled monoshock adjustable for preload, high and low-speed compression and rebound damping.

BRAKES

Front: 320mm petal disc with FTE radial-mount four-pot opposed-piston calliper.

Rear: 240mm petal disc with Nissin twin-piston floating calliper.

TYRES

Front: 120/70 - 17 tubeless.

Rear: 180/55 - 17 tubeless.

DIMENSIONS/WEIGHT

Wheelbase: 1495mm.

Seat height: 918mm.

Dry weight: 128kg.

FUEL TANK

7.8 litres.

TOP SPEED

158km/h (measured)

SERVICE INTERVALS

60 hours.

PRICE

R81 995.

RIVALS

Suzuki DR-Z400 SM - R68 650

Yamaha XT660X - R79 588

Husqvarna SM510R ie - R89 990