Happy 30th Birthday K Series

Happy 30th Birthday K Series

It was 30 years ago on October 3, 1983, at the Paris motor show when BMW Motorrad took a leap into the unknown with the unveiling of the four-cylinder K100 and K100RS. It was a quantum leap forward. At the time there had been rumors of a new four-cylinder model, but it was now a reality – and it was unique in the motorcycle world.

The signature BMW Boxer motor had served well since the R32 was first shown at the Berlin motor show 60 years earlier in 1923. But times were changing and the air-cooled two-valve Boxer was beginning to be squeezed out of the market. BMW motorcycles had lost their zip, were expensive, and power was being strangled by increasingly tough pollution laws.

A bold new direction for BMW, the K100RS (left) and K100 in 1983.
A bold new direction for BMW, the K100RS (left) and K100 in 1983.

The bikes were still selling to BMW enthusiasts of course, but in smaller numbers. Meanwhile, the Japanese brands were attracting plenty of new riders. If nothing was done BMW motorcycles could easily have gone the way of many other German brands. Luckily, the R80G/S was an unexpected success and gave BMW Motorrad a bit of breathing space, but action was needed and needed fast!

The first thoughts on a new model line had been brought into play in 1977 when 28-year-old engineer Josef Fritzenwenger proposed the idea of a longitudinal four-cylinder engine with horizontal cylinders. The idea was not a new one. In 1904, Belgian manufacturer FN had made such a motor creating the world’s first four-cylinder motorcycle.

K100 engine.
K100 engine.

The concept was put to the test using a Peugeot 104 car motor, which had been shoehorned into a modified frame. It showed promise but it was too bulky and heavy. A small BMW car motor was also tried, but it too, was less than ideal for two-wheeled applications. There was light at the end of the tunnel, so work continued, but with no real urgency.

The fortunes of BMW Motorrad had gone downhill and at the end of 1978, the BMW Board removed all senior executives. On January 1, 1979 a new team headed up by Eberhardt Sarfert took over and they were quickly brought up to speed on developments. On February 20th of that year the BMW Board gave final approval for the new project. The K589 project was a leap into the unknown but it had to be done.

A team of 250 people was assembled to work on various areas of the motorcycle project. Martin Probst headed up engine development and, along with Stefan Pachernegg looking after design, the team got down to work. This was now a mission to save BMW motorcycles. If they failed it could be the end of BMW motorcycle production.

A target of 90 hp was the aim and Bosch LE-Jetronic fuel injection would replace carburetors. Surprisingly, the two-valve format was preferred to four-valve. The motor was coming together but the problem was incorporating the gearbox and shaft drive in a package that was both usable and neat. As motorcycles are a visual medium, engineering cannot be ‘tucked away’ in the same way as it can be in cars.

The answer was the Fritzenwenger-patented, Compact Drive System with Monolever swingarm. This innovative solution combined all the elements in a strong unit that, importantly, did not increase the wheelbase. The DOHC A30 motor with clutch, starter motor and fuel injection unit in place weighed only 169 lbs. (76.5 kg). This part of the concept was spot on.

The Fritzenwenger-patented, Compact Drive System with Monolever swingarm,
The Fritzenwenger-patented, Compact Drive System with Monolever swingarm,

The overall design of the bike was a bit more problematic. There had been no real changes in BMW motorcycle design since the /5 series in 1969. The R90S was elegant and the R100RS, with its wind tunnel designed fairing, had broken new ground but the platform was the same. There was now a lack of design experience (in new motorcycle design) so the car design department was drafted in to help. It was a totally new model and it needed a new design language.

The result was a design that was fresh and modern but with a definite BMW feel. The engine was visually integral to the total package. The naked K100 had a real muscular stance and the faired RS displayed an elegant sporting look, accentuated by the rear view mirrors incorporated into the fairing. The car connection could be seen in the BMW kidney design incorporated into the radiator shroud.

This was a major undertaking and nothing was left to chance. As the doors opened to the Paris show, the first ride reports were already starting to appear in the press. At that time, it was unusual to let the press ride a new model prior to its launch but this was different. BMW Motorrad realized it needed to have a multi-pronged strategy. In the weeks leading up to the Paris show, selected journalists were secretly assembled in the south of France. They would be the first outsiders to ride the K100 and their deliberations on the new bike would be critical to its immediate acceptance. They were impressed and their ride reports fueled the story of the release of the bike.


With 90 hp (66 kW), the 539-pound (239 kg) (wet) K100 and 549-pound (249 kg) K100RS took BMW into a new performance era. They gave BMW motorcycles a new life and created a package that opened up the brand to new riders and was also largely accepted by the BMW traditionalists. In 1984 over 30,000 K Series bikes were sold worldwide

The K Series would later expand with the addition of the RT and LT models, K1 and the introduction of four-valves and the 130 hp K1200RS. The old K motor remained in service until the demise of the K1200LT in 2010. Thirty years ago the K Series took BMW Motorrad into the a new era, an era that continues today with the six-cylinder K1600GT and GTL and the four-cylinder K1300S and K1300R.

K1300S 30th Anniversary Special Edition

If you’re lucky enough to still find one, the 30th anniversary of the K Series is being celebrated by the launch of a special edition K1300S. Unveiled at last year’s autumn shows, the “30 Years K Model” anniversary K1300S is painted in fresh Alpine White and stylish Sapphire Black metallic, crowned with fiery Racing Red. It features ABS as standard, electronic suspension adjustment ESA II, a safety package with Tire Pressure Control and ESC Electronic Slip Control. Add to that an HP shift assistant that allows fast up-shifting without having to throttle down and use the clutch, and a titanium Akrapovič silencer, and you have an exclusive K Series that will surely look and perform beautifully for at least the next three decades!

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