IT IS NOT only ageing rock stars that make dramatic comebacks. BMW's traditional flat-twin 'boxer' bike engine has done the same thing. This year marks BMW's 70th anniversary, and from the boxer's first appearance in 1923 - its cylinders 'punch' out sideways in front of the rider's shins - it was as integral a part of the German firm's image as the famous propeller badge.

Until, that is, about 10 years ago, when the old air-cooled boxer seemed bound for museum status, a victim of emission controls and the desire for improved performance. BMW introduced a new 'K' series of more sophisticated, water-cooled three- and four-cylinder engines. But demand for the traditional twins remained strong, several models were reprieved and updated, and BMW's management thought again.

The result is the R1100RS, powered by a new-generation boxer designed to take BMW into the 21st century.

Although its basic layout is the same, the new 1,085cc engine has little in common with its predecessors. Its specification is modern, featuring electronic fuel injection, four valves per cylinder (operated not by old-fashioned pushrods but by a single camshaft in each cylinder head), and cooling by a combination of air and oil. In the BMW tradition, final drive is by shaft instead of chain.

The new bike also contains some futuristic features. At first glance the RS looks to have conventional telescopic front suspension, but its forks contain no springs. Instead, a single, central front shock absorber is operated by a horizontal arm running from midway down the forks to a pivot at the engine. The main advantage of BMW's 'Telelever' is that, like the forkless system of Yamaha's GTS1000, it reduces dive under braking and so increases stability.

Most suspension forces are borne by the immensely strong engine, through the horizontal arm, so that the RS barely needs a frame. A small steel subframe runs upwards to support the front suspension and bodywork that includes the fuel tank and fairing. Another subframe bears the seat and the central, vertical rear shock absorber.

Sleek if unexceptional styling hides another innovative touch: the way in which the RS's screen, handlebars and seat can be altered to suit its rider. A similar type of adjustment has long been commonp1ace in cars, but until now has not been available on a production motorcycle. (Other advanced features, at least by bike standards, are its anti-lock brakes and optional catalytic converter.)

Unusually, then, the RS requires a little fine-tuning before setting off. Being tall, I put the seat on the highest of its three settings for maximum leg-room, and wound the screen almost vertical to divert as much air over my head as possible. On standard setting, the flat handlebars completed a roomy, slightly leant-forward riding position as I headed off through darkness and driving rain on my first serious trip.

In such unpleasant conditions, the BMW really shines. The big motor delivers a respectable maximum of 90bhp, good for a top speed of about 135mph.

More importantly, it allows relaxed yet rapid cruising, the flat-twin layout giving a long-legged feel with a minimum of troublesome vibration (just enough, unfortunately, to blur the mirrors at most speeds). The five-speed gearbox is rather imprecise, but the fuel-injected engine's crisp mid- range response makes for a minimum of gear changing.

The RS's handling also contributes to the bike's easy speed and refined feel. The innovative front end works well, allowing a soft ride, yet remaining stable even under hard braking (in marked contrast to BMW's horribly dive-prone telescopic systems of a few years ago). The rear suspension is also good, combining with the bike's low centre of gravity, grippy Michelin tyres and powerful disc brakes (BMW's second-generation anti-lock system is a noticeable improvement) to aid wet-weather safety and encourage enthusiastic cornering on dry roads.

Long trips and bad weather emphasise the bike's comfort and the value of typical BMW features such as the generous fuel range (the five-gallon tank allows for almost 200 miles), dashboard clock and fuel gauge, heated handlebar grips and capacious, quickly detachable plastic panniers. Unfortunately, all but the first of these are optional extras, adding more than pounds 500 to an already steep pounds 8,485.

BMW's bikes have never been cheap, though, and the RS adds to the marque's familiar quality a blend of traditional virtue and modern technology that the competent but less charismatic K-series multis cannot match. The boxer may have been on the ropes for a while, but with the R1100RS it is back with a punch.

(Photograph omitted)

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