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BMW K 1200 RS: development
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The developers worked for a good three years to crown the BMW program. With the new K 1200 RS.
The large room in the heart of the BMW Research and Engineering Center FIZ looks like a mixture of gymnasium and theater hall. Located in the middle of the sanctuary, it is usually used for presentations of the highest quality: the valued board members can check variants of a car or motorcycle on several revolving platforms before they raise or lower their thumbs. David Robb, Head of Design for the BMW motorcycle division, has placed his latest creation on the stage right by the wall-sized window. In the best light. Sketches, plasticine models, first test vehicles – the 41-year-old American has worked on this motorcycle over and over again over the past three and a half years. He has also been familiar with the end product, which was presented at IFMA in October, for many months. Nevertheless, he is filled with genuine pride when he invites visitors to the window. “Look, we tried to combine strength and lightness.”
It is not difficult to see where the power center is in the K 1200 RS: the one-piece flank of the fairing and tank shell arches upwards and reaches its greatest, quite impressive width just before the driver’s knees. The newly designed valve cover peeps out of a small recess in the left side, on the other side this hole in the tight-fitting plastic cover allows access to the oil filler neck. An engine spoiler rounds off the encapsulation under the two large side panels, and a narrow web closes the gap at the top. “This bridge has a fold at its lower end into which both side parts are hung; A few screws are enough to fasten them. “The practical attachment goes back to a dictation of the production and service managers, the almost hidden arrangement of the screws on the designer:” Highest possible quality all round. “
Then Robb flatters the curves of the K with his hands. “No rigid lines, lots of surprises. From every perspective. «In staccato he formulates the independent formal approach of the newcomers. Now he refers to the bulges at the bottom of the upper part of the fairing: “Here is a classic K-element that ensures recognition.” The appendages conceal the indicators in the front part. Air ducts inside protect the driver’s hands from storm and rain, because they have been perfected in the wind tunnel so that the current drifts to the side. The sporting accent that BMW hadn’t expected in this form is, of course, set by the rear: Only a massive stainless steel silencer, which Japanese athletes could hardly wear, obstructs the unobstructed view of the five-spoke rim, which is reinforced with a 170 tire. Rising lines, a slender bench and a tightly dimensioned splash guard complete the dynamic ensemble. Viewed in this way, the RS cleverly denies its 285 kilograms curb weight.
»You don’t feel it either.« Jurgen Bachmann, the engineer responsible for the entire series, and his team of colleagues have set out to explain the K concept technically. Like all technicians, the BMW people were faced with several conflicting goals: First, their sports tourer should be as nimble as it looks and at the same time be able to cope with the BMW-appropriate payload of 215 kilograms. Second, the strong vibrations of the K four-cylinder could only be dealt with with a heavy construction effort or with an expensive new design.
But one after the other: Out of a fundamental interest, but definitely with a view to the coming K generations, BMW has checked the steering knuckle. However, the hoped-for results did not materialize and work was stopped in mid-1992. “First of all,” as they say, because the GTS 1000 from Yamaha presented in the same year surprised the Munich company. Nevertheless: The K 1200 RS prescribed the in-house Telelever in the specification sheet, drawn up at the beginning of 1993. As is well known, the swing arm of the BMW boxer models is located directly in the engine, the fork legs are supported by a subframe connected to the engine, and the R rear swing arm rotates in the transmission housing.
In order to implement this principle in the K, however, the engine would have to vibrate less: the 1100 already had a lack of smoothness, while in the 1200 with a larger stroke with the same connecting rod length, the second-order inertia forces increase even further and exacerbate the problem. As a result, an attempt was made to tame the lying foursome with two balancing shafts, but their sensible arrangement always collided with the suitable bearing points for the Telelever. However, there was no green light for a completely new design, including the immense follow-up costs, and so two concepts were developed in autumn 1993: BMW itself created a vehicle with a load-bearing engine and a decoupling of the seat, pegs, handlebars and one mounted directly in the transmission Swing arm. At Bimota in Rimini, a self-supporting frame and a totally decoupled drive unit as well as a swing arm bearing in the frame grew according to BMW plans.
The techno-tourism resulting from the spatially separated development was definitely wanted. Jurgen Bachmann: “First of all, because of the fruitful exchange of ideas with the flexible Bimota people. Secondly, the capacities in Munich do not allow for double development, and thirdly, this made contact with the frame manufacturer Verlicchi easier. «The travel activities continued to grow because the Munich variant with its many damping elements did not convey a precise driving experience: In August 1994, the decision was made in favor of the self-supporting one Frame.
After initial trials with a hand-welded frame – “It’s really great what they put together.” – an extruded aluminum profile construction, a bolted combination of cast aluminum and steel pipes, and a welded cast aluminum structure went on the road. The latter ultimately won the race because its design adapts better to the shape of the engine and transmission, is more rigid and, on top of that, is easier to reproduce in series. Jurgen Bachmann sums up the customer benefits: “With the self-supporting frame, we achieve a very specific driving experience and at the same time almost complete freedom from vibration for driver and front passenger.” He puts the weight disadvantage compared to a R 1100 RS solution at “around seven to eight kilograms «. In contrast to the 70 percent for the Boxer RS, the brake buckling compensation, which thanks to Telelever could be practically 100 percent, was set at 90 percent.
The work of the engine specialists, on the other hand, is rather unspectacular: With the same bore of 70.5 millimeters – the K-Block can not handle more – a stroke extended by five to 75 millimeters produces the desired almost 1200 cubic centimeters of displacement. The compression, which is moderately increased from 11 to 11.5: 1, improves the thermal efficiency, so it helps to achieve the required increase in torque. Lighter crankshafts, box pistons and valves increase the speed stability, because the targeted performance zenith could only be reached with higher speeds: the open version develops 130 hp, and so the renovation of the K-engine, which ultimately did not remain the same, made for the political Sensation of this new BMW.
Head of Development Wolfgang Durrheimer explains the new Bavarian power behavior: “There are markets that demand more than 98 hp from a sports tourer. We took that into account very early on. «The performance curves show that the result is an extremely powerful 98 hp variant in the lower engine speed range, which the open one should easily drive away in pulling through up to 140 km / h. Despite the very independent curves, the throttling takes place »only« via a modified map and different intake manifolds. And: Both maps are already programmed in the also revised Motronic. In order to get from 98 to 130 HP, you only have to remove a Motronic connector and mount another airbox with shorter suction pipes.
BMW broke new ground with dynamic pressure charging, which has long been common practice in Japan, while extensive tests with a wide variety of camshafts have recently led to: “We achieve the best performance values with the 284-degree shaft from the K 1,” reveals engine man Georg Mittler . Completely new – for BMW – the six-speed gearbox, a development by the supplier Getrag. Of course, it should cure the old ailments of poor shiftability and high shifting forces. Hydraulic clutch actuation was also required, but why six gears with such a powerful engine? “Because we wanted to adapt the increments optimally to the engine output,” comments Mittler soberly. Jurgen Bachmann continues: “Because it’s fun.” The fact that the rocker arm isn’t in the new box doesn’t mean that it won’t move over to the R-row at some point. “All you need is a different housing.”
B.What remains is what is commonly summarized under trimmings: Of course, these BMWs also feature regulated catalytic converters and ABS, even as standard. Of course, she can carry suitcases on nicely made and extremely delicate straps. It is logical that BMW has refined its unique selling proposition ergonomics package, because that can be marketed well as long as everyone else is sleeping. In addition to the adjustable windshield and seat, there are now adjustable notches and handlebar halves. Sure, you want to finally try it all out. “Sorry,” says Jurgen Bachmann, “sales start at the end of February and beginning of March. And besides, it just started to snow.
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