Kevin Ash tests new KTM 690s: the Duke, Supermoto and Enduro

We see it time and again: even at the cutting edge of motorcycle design, there is no substitute for experience and tradition. BMW makes all sorts of bikes these days, but is still at its best with tourers. The core of Austrian KTM, meanwhile, is in off-road bikes with single-cylinder engines and, sure enough, its three latest machines, the 690 Duke, 690 Enduro and 690 Supermoto, are powered by the best road-going single you'll find from any manufacturer.

The sheer power of the engine is genuinely astonishing. Ignore the 690 designation as the capacity is just 654cc, so there's only one 102mm piston pushing you along, yet the engine revs freely and happily into its 8,000rpm red zone, enough in top gear for almost 120mph. That's a huge advantage over most singles in this class: they usually struggle to top 100mph, which makes them breathless at motorway speeds. Not the Duke, which backs up the top-end hit with a muscular mid-range and pretty impressive low-rev pull, too. It's also surprisingly smooth, considering that sole piston hammering up and down, although the vibrations might still get to you at sustained high speeds.

The Duke name is important to KTM as it dates back to 1994 when the company released the original as its first pure road bike. Until then the factory had specialised in off-road machinery, but decided its future would be more secure, and lucrative, if it dipped into the road bike market.

The Duke was, and still is, very much a niche model in the UK (although it does well in some other European markets), but for those riders it suits, it suits them very well indeed. Primarily it's a bike for back-road fun, charging up mountain passes, chucking around tight country lanes, practising your wheelies and generally doing things your mum wouldn't approve of. But it does double up as a handy commuter, agile and easy in traffic. Despite its wilder side, it can easily be tamed for inexperienced riders as beneath the seat is an adjuster that selects one of three engine-management maps. The gentlest one cuts maximum power by about 30 per cent and softens the power delivery, although, realistically, this has limited use on the road as the bike is perfectly manageable anyway - the setting is much more useful on the 690 Enduro off-road. The third setting gives the same maximum power but with a much more aggressive delivery, boosting excitement, although when you're tired it can be hard work, and it might be a handful in the wet.

It's a pretty sharp-handling machine, thanks partly to its light weight of just under 330lb and also the decent quality suspension - KTM owns prime suspension maker WP, and makes full use of it. But I wasn't always completely comfortable pushing the bike very hard around corners as it loses some of its feedback and the steering becomes a touch vague in comparison with a dedicated sports bike.

At the other end of the spectrum, it is more comfortable than I was expecting - dirt bikes have vestigial seats and KTM's lack of experience in bottom cossetting has often showed on its road bikes. Despite being quite narrow, however, the Duke's is not too bad. You'd even consider a short tour on one - the three-gallon tank would be adequate for this if you found the resolve not to wind the throttle open to the stop all the time.

It's a real head-turner as far as looks are concerned. KTM is the only bike manufacturer to make a success of this sort of angular styling, and on the Duke it's lean and aggressive yet well balanced and attractive - as well as being unmistakably a KTM. For your money you also get high-quality equipment, including British-made Renthal handlebars, Brembo brakes and Marchesini wheels, which all go some way towards justifying the price. But at £6,195 it's still costly and, despite the performance, still a single. There are many exciting Japanese and Italian machines available for much less, and most are more versatile. KTM's dealer network is small and doesn't have a great reputation either.