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BMW K100
BMW K100
BMW K100
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BMW K100
BMW K100RS
ManufacturerBMW
Also called"Flying Brick"[1]
Production1982–1992
AssemblySpandau, Germany
Classstandard, sport touring
Enginelongitudinal DOHC I4, 987 cc (60.2 cu in)[2]
Bore / stroke67 mm × 70 mm (2.6 in × 2.8 in)[2]
Compression ratio10.2:1[2]
Top speed137 mph (220 km/h)[3]
Power90 PS (66 kW) @ 8000 rpm[4]
Torque63.3 lb⋅ft (85.8 N⋅m) @ 6000 rpm[3]
Ignition typeBosch LE-Jetronic[2]
Transmission5-speed sequential manual transmission, counter-rotating clutch,[3] shaft drive[2]
Frame typetubular steel, open cradle with engine as stressed member
Suspensiontelescopic forks, single-sided swingarm
Brakestriple discs
Wheelbase1565 mm (Unladen)
Seat height800 mm
Weight536 lb (243 kg)[3] (wet)
Turning radius5.1m
RelatedBMW K75
BMW K1

The BMW K100 is a family of four-cylinder 987 cc motorcycles that were manufactured by BMW from 1983 to 1992.

Background

[edit]

As the 1970s came to an end, BMW faced three problems from developing its flat-twin boxer engine further:

  • Emissions regulations being developed in the United States and the European Union meant that more control was needed over the amount of fuel entering the combustion chamber. From an engineering standpoint, this was easier to achieve with more cylinders at an overall smaller displacement.
  • The market-led development of bikes was leading to the Japanese factories developing smoother and quicker machines based around a four-cylinder format.[5]
  • Bike comparison in the media at the time was based around top speed, and a four-cylinder when fully developed created more power.

In combination, this meant that BMW's marketing to users of a superior bike, allowing them to price at a premium, was being quickly lost, resulting in a loss of sales and market share.

At the time, BMW, Moto Guzzi, and Harley-Davidson were the only major "high end" manufacturers that did not offer liquid-cooled engines. Competing brands, notably of Japanese manufacture, were touting the superiority of their liquid-cooled engines and had introduced low maintenance shaft-drive technology in a growing number of their models.

Concept

[edit]

BMW needed to develop a clean-burning four-cylinder engine quickly. While a flat-four engine would have been suited to their boxer tradition and experience, it would also give the appearance that they were copying Honda's GL1000 Gold Wing.[6]

In 1977, Josef Fritzenwenger presented a prototype using a PSA-Renault X-Type engine from a Peugeot 104.[7] The engine, which was installed in the 104 at a 72° angle, was laid flat in the frame with the crankshaft on the right, running parallel to the centre line of the frame.[5] This layout, for which BMW submitted a patent application, was well suited to BMW's traditional shaft drive, needing only one 90° bevel drive to transmit power to the rear wheel. Using shaft drive with the near-vertical transverse engine preferred by the Japanese manufacturers at the time would have needed two 90° bevel drives, doubling the power lost to the inefficiency of these units.[2] The new layout also kept the bike's centre of gravity low, which improved the bike's handling, and made space behind the front wheel available for the radiator.

Design and development

[edit]
Closeup picture of BMW K100 engine. Also shows some black bodywork, forks and a front brake caliper
K100 engine closeup

Fritzenwenger's concept was developed by a team led by Stefan Pachernegg[3] based on criteria set out by R. P. Michel and K. V. Gevert. Martin Probst, who had earlier worked with the development of BMW's Formula Two engine, was responsible for engine testing and development.[2]

As an automobile manufacturer, BMW had about twenty years of experience with liquid-cooled overhead camshaft inline engines. This was carried over to the K100 engine, which used a Bosch LE-Jetronic fuel injection similar to that being introduced on their second generation 3 Series cars.[8] Replacing the Bing carburettors traditionally used on BMW motorcycles, the fuel injection system increased power, broadened and smoothed the powerband,[citation needed] and reduced fuel consumption, partly by shutting off fuel under deceleration to 2000 rpm.[2] The engine also featured a breaker-less electronic ignition system.[2]

The engine was positioned with the crankshaft on the right-hand side of the motorcycle and the cylinder head, camshafts, injectors and spark plugs on the left-hand side. This improved access to the engine over that of a conventional design, where the crankshaft would be at the bottom and the cylinder head and associated parts would be between the engine block and the upper frame.

K75

[edit]
BMW K75
Blue BMW K75 fitted with topbox, parked in a pedestrian area
1993 BMW K75
ManufacturerBMW
Production1985–1995
AssemblyGermany
ClassStandard
EngineLongitudinal DOHC I3, 740 cc (45 cu in)[9]
Bore / stroke67 mm × 70 mm (2.6 in × 2.8 in)[9]
Compression ratio11.0:1[10]
10.5:1[9]
Top speed131 mph (211 km/h)[citation needed]
Power75 hp (56 kW) @ 8000 rpm[citation needed]
Torque50 lb⋅ft (68 N⋅m) @ 6000 rpm[citation needed]
Ignition typeBosch L-Jetronic[9]
Transmission5-speed sequential manual transmission,[9] shaft drive
Frame typeTubular steel, open cradle with engine as stressed member
SuspensionTelescopic forks,[9] single-sided swingarm
BrakesDual front discs and single rear disc,[9] or rear drum
Rake, trail27.5°/3.98 in (10.1 cm)
Wheelbase59.7 in (152 cm)[9]
DimensionsL: 87.4 in (222 cm)
W: 35.4 in (90 cm)
H: 51.2 in (130 cm)
Seat height31.9 in (81 cm)[9]
29.9 in (76 cm) (low seat)
Weight505 lb (229 kg) (dry)
536 lb (243 kg) (wet)
Fuel capacity5.54 US gal (21.0 L)
Fuel consumption59 mpg‑US (4.0 l/100 km)
RelatedBMW K100
BMW K1
Black BMW K75T with top box and panniers, parked on a driveway in front of a house and metal gates
1987 BMW K75T

The BMW K75 is a standard motorcycle produced by BMW Motorrad from 1985 to 1995.

The three-cylinder BMW K75 was developed alongside the K100, but was introduced a year after the K100 as a marketing strategy.[10][11] The K75 engine had the same bore and stroke as the K100, yielding a displacement of 740 cc.[11] Its crankshaft had 120° between the throws[12][13] and was counterbalanced by balance weights added to the water pump accessory shaft, which ran at engine speed as is correct for a 120° straight-three engine.[10] The balance shaft made the K75's engine smoother than the K100's engine.[10][14] To increase the smaller engine's power, the K75's engine was given longer valve timing,[10] the compression ratio was increased to 11.0:1 from the K100's 10.2:1,[10][15] the combustion chambers were redesigned, the intake manifold was shortened, and the exhaust system was retuned.[15] The US market engine, specified to meet Environmental Protection Agency (EPA) requirements, produced 68 hp (51 kW); engines for all other markets produced 75 hp (56 kW).

K75 valve cover

The front engine mounts on the K75 frame are placed further back than in the K100 frame and the downtubes are at a different angle; otherwise, the frames are identical. The K75 had the same wheelbase, seat height, and steering geometry as the K100.[10] According to BMW, 80 percent of the K75's parts are interchangeable with the K100's.[11] The K75's radiator and fuel tank were smaller than those on the K100.[10]

Specifications

[edit]

A single-sided hollow swingarm enclosing the drive shaft provides the right-side drive through the gearbox and to the rear wheel. The 4-into-1 all stainless steel exhaust exits on the left-hand side.

Brakes are two-piston Brembo calipers onto undrilled discs. Two different fork manufactures are used: Showa with an outer upper tube diameter of 1.612 in (40.9 mm) and Fichtel and Sachs measuring 1.627 in (41.3 mm).

K100 models

[edit]
K100RT
  • K100, with no fairing
  • K100RS, with sports fixed fairing and lower handlebars
  • K100RT, with full touring fairing
  • K100LT, with higher screen and additional standard equipment for 'Luxury Touring'
  • K100TIC, developed as an Authorities vehicle to support a variety of emergency services configurations including Police, Ambulance, Fire, and Military, this model designation only existed until the end of the 1985 model year. It was equipped with a high output alternator, taller first gearing, and supplementary wiring harnesses to support a variety of equipment options

All K100 models have dual front and single rear disk brakes. The RS model has taller gearing than other models.[16]

The K-series has additional refinements including aluminium fuel tanks,[14] adjustable headlights, high capacity 460 watt alternators, Hella accessory plug-in, and self-cancelling turn signal lights.

K75 models

[edit]
Red BMW K75S with top box and panniers, parked on a city street
K75S with belly pan and touring bags
  • K75, a naked bike with no fairing
  • K75T, a US-only touring model with a windscreen, touring bags, engine crash bars, and a rear top case[citation needed]
  • K75C, with a small cockpit fairing mounted to the handlebar[17]
  • K75S, with sport fairing, stiffer suspension, and lower and narrower handlebars[18]
  • K75RT, with full touring fairing[19]

The S and RT versions have a rear disc brake and 17" rear wheels, whereas the others have a single leading shoe drum brake and 18" rear wheels. A stiffer "anti-dive" front suspension was added to the S and RT models. The later RT versions had an adjustable windshield that could be raised and lowered. Some taller riders complained of wind buffeting with the smaller S model stock windscreens.[citation needed]

Later developments

[edit]

The same team later developed an improved four-valve-per-cylinder head for the aerodynamic K1. In later models, the standard swingarm was replaced with a Paralever as on the K1.[citation needed] The LE Jetronic fuel injection system with separate ignition management was replaced by Motronic engine management with the introduction of four-valve cylinder heads with the 1990 K1 and the 1991 K100RS.[8]

Anti-lock brakes (ABS) were developed for K100 and K75 motorcycles and were installed on later models, which were among the first production motorcycles with this feature.[14]

In 1993, the fork used on the K75S was replaced by a 41 mm (1.6 in) Showa fork. In 1994, the electrical system was given a larger 700 watt alternator and a smaller 19 Ah battery.[9] For 1995 anti-lock braking was standard on the K75S.[20] Two different forks manufacturers were used: Showa with an outer upper tube diameter of 1.612 in (41 mm) and Fichtel and Sachs measuring 1.627 in (41 mm).

Sales

[edit]

Although sales were initially modest, buyers eventually warmed to the multi-cylinder BMWs. The K100 was a relative sales success, stemming the losses to the Japanese and changing the media and public perception of BMW.

The four-cylinder engine suffered from secondary vibration, but the three-cylinder K75, with its balance shaft, was far smoother.[14] The engineers had anticipated this and had designed in excellent vibration isolation, but it was the only technical glitch.

The competition was never far behind in performance on the launch, updates were modest, while engine performance was stepped up with the September 1988 launch of the radically aerodynamic BMW K1.

Notes

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

BMW K100

View on Grokipedia
from Grokipedia
The BMW K100 is a family of touring motorcycles manufactured by from 1983 to 1992, notable for introducing the company's first inline-four-cylinder engine in a production bike, marking a shift from traditional air-cooled boxers to a water-cooled, longitudinally mounted powerplant with shaft drive. Developed over five years with extensive testing—including 10,000 dyno hours and 400,000 km of road evaluation—the K100 series was BMW's response to tightening emissions regulations and intensifying competition from Japanese manufacturers like and Kawasaki, whose multi-cylinder models had gained popularity in the late . The base model's 987 cc liquid-cooled, DOHC inline-four engine, featuring two valves per cylinder and Bosch L-Jetronic electronic , produced 90 hp (66 kW) at 8,000 rpm and 63 lb-ft (86 Nm) of torque at 6,000 rpm, delivering smooth power delivery and a top speed of approximately 135 mph (217 km/h) while achieving around 48 mpg (4.9 L/100 km) . The K100's engineering innovations included a low center of gravity from the engine's 90-degree rotation, a spaceframe using the powerplant as a stressed member, dual 285 mm front disc brakes with twin-piston calipers, a single 285 mm rear disc, and a 22-liter (5.8 US gal) , resulting in a wet weight of 249 kg (549 lb) and a height of 810 mm (31.9 in). Variants expanded the lineup to suit different riders: the standard K100 (naked street bike), the sport-oriented K100RS with a half-fairing (later upgraded to a 16-valve head yielding 100 hp from 1989), the touring-focused K100RT with full fairing and luggage, and the long-distance K100LT adding amenities like a larger and heated grips; a three-cylinder sibling, the K75, joined in 1985 with a detuned 740 cc version of the producing 75 hp. Praised for its reliability, vibration-dampened ride (enhanced in later rubber-mounted models), and optional (ABS) introduced in 1988 as the world's first on a , the K100 series sold over 60,000 units and earned nicknames like "Flying Brick" for its robust aluminum engine block, influencing BMW's subsequent K-series and solidifying the brand's reputation for engineering excellence in the 1980s touring segment.

Development History

Origins and Background

In the , BMW's longstanding dominance in the market with its air-cooled flat-twin engines faced significant challenges from Japanese manufacturers, who introduced advanced inline-four and V-four configurations that offered superior smoothness, power, and reliability. Models such as Honda's CB750 Four (1968) and later the Gold Wing (1974) and CBX (1978), along with Kawasaki's Z1 (1972) and Yamaha's XS1100 (1978), captured growing market share in touring and sport segments, pressuring BMW to innovate beyond its traditional R-series lineup. The exacerbated these competitive dynamics by driving demand for fuel-efficient vehicles amid rising gasoline prices and economic uncertainty, compelling manufacturers to prioritize high-performance designs that balanced power with economy. This global event, combined with stringent anti-pollution regulations like those in , highlighted the limitations of BMW's older boxer engines in meeting evolving environmental and efficiency standards. By the late , BMW's internal strategy shifted toward modernizing its motorcycle division, moving away from the R-series air-cooled twins and abandoning earlier pursuits of the due to reliability and emissions issues. The was initiated around under the of engineers like Josef Fritzenwenger, drawing on shared technology from BMW's automotive division, including systems originally developed for cars. This effort culminated in the introduction of the K-series family in , marking BMW's entry into liquid-cooled, four-cylinder motorcycle production.

Concept and Initial Design

The BMW K100 represented a radical departure from BMW's longstanding tradition, introducing a liquid-cooled, 987 cc inline-four configuration designed for smoother power delivery, reduced vibration, and significantly higher output compared to the air-cooled boxers. This shift was driven by the need to compete with advanced Japanese four-cylinder motorcycles while meeting stricter emissions standards and improving overall refinement for long-distance touring. The engine's longitudinal mounting—aligning the parallel to the bike's length—facilitated a , straight-line shaft drive, minimizing torque reaction and maintaining BMW's preferred philosophy without the complexity of bevel gears used in transverse setups. Drawing on expertise from 's automotive division, the K100's engine incorporated advanced components such as Bosch L-Jetronic electronic system originally developed for cars, ensuring precise control and low emissions. The aluminum block featured Scanimet-coated cylinders—a nickel-silicon-carbide process akin to —for enhanced durability and heat dissipation, with siamesed bores spaced at 74 mm centers and a bore/stroke of 67 x 70 mm. Initial prototypes in 1977 tested the concept using a 104's liquid-cooled inline-four engine mounted longitudinally in a modified frame, validating the layout's potential for a low center of gravity before engineers crafted their own double-overhead-cam design with two valves per cylinder. Design goals centered on achieving approximately 90 horsepower at 8,000 rpm, with emphasis on strong low-end peaking around 6,000 rpm to suit loaded touring scenarios, and a broad powerband for effortless highway cruising. The platform was engineered for , allowing easy adaptation to three- or six-cylinder variants by sharing core components like the and transmission. During the 1980-1982 development phase, early sketches and prototypes prioritized through wind-tunnel testing, resulting in faired models with adjustable airfoils to reduce drag and buffeting, alongside ergonomic refinements such as a 32-inch seat height, rear-set pegs, and a slightly forward-leaning riding position for all-day comfort.

Engineering Challenges and Testing

The development of the BMW K100 required overcoming significant technical hurdles over a five-year period beginning in 1978, leading to its production debut in 1983. This timeline encompassed rigorous prototyping and validation efforts, including 10,000 hours of testing to evaluate engine performance under controlled conditions and 400,000 kilometers of road trials spanning diverse terrains in and the . These tests were essential to verify the motorcycle's and refine its handling characteristics before market introduction. A major challenge was mitigating inherent to the longitudinal inline-four-cylinder , which could transmit unwanted oscillations to the rider. BMW engineers addressed this by incorporating counter-rotating and components, whose combined mass effectively canceled lateral reactions from the , resulting in smoother operation compared to typical transverse four-cylinder designs. Integrating the shaft drive system without exacerbating reaction—such as unwanted lifting or squatting during acceleration—posed another obstacle, particularly with the initial Monolever . This was resolved through the subsequent adoption of the Paralever system, featuring a parallel linkage and anti-torque arm that distributed drive forces more evenly to the frame, enhancing stability. Refining the liquid cooling system for reliable, consistent performance in a compact presented further difficulties, as it needed to maintain optimal temperatures across varying operating conditions without excessive weight or complexity. Leveraging BMW's two decades of automotive experience with liquid-cooled inline engines, the team developed and iterated on the cooling and circuits after the powerplant's inaugural run on August 18, 1980, incorporating multiple measurement points to monitor and adjust . During this phase, innovations like the double overhead camshaft (DOHC) valvetrain with two valves per cylinder underwent extensive bench and on-road validation to ensure precise timing and longevity under high-rev loads. The Bosch L-Jetronic system, which synchronized fuel delivery with airflow for efficient combustion, was also thoroughly tested and integrated starting with the 1983 launch, with refinements applied to 1986 models to optimize response and emissions compliance. The engineering effort was spearheaded by a dedicated team, including key figures such as project heads Wolfgang Aurich, Karl H. Gerlingen, and Eberhardt Sarfert, with substantial cross-division input from the automotive sector to adapt car-derived technologies like liquid cooling and electronic fuel management to demands. This collaborative approach ensured the K100's innovations met stringent reliability standards through iterative problem-solving and real-world validation.

Model Variants

K100 Series Models

The BMW K100 series, produced from 1983 to 1992, encompassed several variants built around a shared inline-four engine platform, with the base model serving as the foundation for more specialized versions tailored to different riding preferences. These models emphasized innovation in layout and shaft drive, offering a versatile range from standard to luxury touring configurations. The base K100, introduced in 1983 and produced until 1990, was a naked standard delivering 90 horsepower and designed for everyday versatility across urban and highway use, with a total production of 12,871 units. Lacking extensive bodywork, it prioritized simplicity and direct handling, making it suitable for riders seeking a no-frills introduction to the K-series engineering. The K100RS, launched alongside the base model in 1983 and continuing through 1992, was a sport-touring variant featuring a full fairing optimized through wind-tunnel testing for enhanced and higher speeds, reaching up to 220 km/h. Its fixed sports fairing and lower handlebars improved stability during aggressive riding, while from 1988, an optional (ABS) became available, marking one of the first implementations on a production . This model appealed to enthusiasts desiring a balance of performance and long-distance capability without heavy touring accessories. Introduced in 1984 and produced until 1988, the K100RT focused on touring with a full fairing, large color-matched panniers, and an electrically adjustable windscreen to reduce rider fatigue on extended journeys. Its design emphasized comfort through ergonomic seating and weather protection, positioning it as an ideal choice for road trips and professional use, such as by emergency services. The K100LT, debuting in 1986 as the luxury touring flagship and running through 1991, built on the RT with integrated hard luggage, an AM/FM radio-cassette audio system with handlebar controls, heated grips, and a passenger backrest for superior long-haul refinement. With 14,899 units produced, it represented the pinnacle of K100 opulence, incorporating features like a higher and enhanced storage to cater to premium travel needs. In 1989, all K100 variants received an upgraded 16-valve cylinder head, boosting output to 100 horsepower and improving efficiency across the lineup without altering the core architecture. This evolution shared foundational engineering with the lighter K75 series, adapting the four-cylinder layout for broader performance applications.

K75 Series Models

The K75 series was introduced in 1985 as a more affordable counterpart to the K100, utilizing a detuned inline-three-cylinder derived from the same longitudinal layout to provide accessible for a broader market. This lineup shared the K100's and architecture but emphasized economy and lighter weight, with the three-cylinder configuration featuring the same bore and stroke dimensions as the K100's four-cylinder unit but omitting one cylinder for reduced complexity and cost. The base K75, produced from 1985 to 1995, served as the standard naked model with a 740 cc liquid-cooled inline-three producing 75 hp, weighing approximately 505 lb (229 kg) wet for nimble handling in everyday riding. The K75C variant, available from 1985 to 1986, adopted a bagger-style design with a small fairing and , tailored primarily for the U.S. market to appeal to enthusiasts seeking a distinctive . Introduced in 1986 and continuing through 1995, the K75S offered a sport-oriented take with a half-fairing, sportier including adjusted handlebars and footpegs, and enhanced suspension, making it a favorite among riders for aftermarket customization due to its balanced dynamics. The K75RT, produced from 1986 to 1995, functioned as the touring model akin to its K100 counterpart but with the three-cylinder powerplant's emphasis on improved , featuring full fairing, hard luggage options, and comfort-focused seating for long-distance travel.

Technical Specifications

Engine and Drivetrain

The BMW K100 featured a groundbreaking longitudinal inline-four , marking BMW's entry into liquid-cooled, multi-cylinder production. This 987 cc DOHC unit, with a bore and stroke of 67 mm × 70 mm, produced 90 horsepower at 8,000 rpm in its initial two-valve-per-cylinder configuration, delivering smooth power delivery suitable for long-distance touring. The engine's design, inspired by scaled-down automotive principles with Nikasil-coated cylinder bores for , emphasized reliability and low , contributing to the model's reputation as the "Flying Brick." Early K100 models utilized Bosch LE-Jetronic electronic for precise metering, paired with a of 10.2:1 and wet-sump to ensure consistent distribution during extended rides. peaked at around 86 Nm at 6,000 rpm, providing strong mid-range pull that reached 85 percent of maximum by 3,500 rpm, ideal for highway cruising without excessive revving. Starting in 1990, the engine evolved to a 16-valve DOHC setup with engine management for improved emissions compliance and efficiency, boosting output to approximately 100 horsepower while enhancing throttle response and smoothness. The K75 variant, introduced as a more compact option within the K-series, employed a 740 cc DOHC inline-three sharing the same longitudinal mounting and liquid-cooling , but with a 120-degree and dual balance shafts for refined vibration control. This configuration delivered 75 horsepower at 8,500 rpm, offering ample performance for its displacement while maintaining the series' emphasis on balance and longevity, fueled by similar LE-Jetronic injection. The across K100 and K75 models centered on a robust five-speed sequential gearbox integrated with the engine as a stressed chassis member, transmitting power via a shaft drive system known as the Compact Drive. This setup minimized maintenance compared to drives and provided torque reaction management through a single-sided Monolever in early iterations. From 1988, later models including special editions and variants like the RT and 16-valve versions adopted the Paralever shaft drive, which used a linkage to virtually eliminate shaft-drive "jacking" effects, improving stability under acceleration and braking.

Chassis, Suspension, and Brakes

The BMW K100 featured a tubular steel designed as an open cradle, with the longitudinal inline-four serving as a stressed, load-bearing member to enhance overall rigidity and stability. This construction contributed to one of the stiffer motorcycle of its era, particularly when combined with the engine's placement, and the modular frame design facilitated adaptations for variants like the three-cylinder K75. The measured 1,520 mm (59.8 in), providing a balanced foundation for long-distance touring. Suspension on the K100 consisted of a front telescopic fork with hydraulic damping, featuring 41 mm diameter stanchions and 185 mm (7.3 in) of wheel travel for composed handling on varied roads. At the rear, a single-sided swingarm employed BMW's Monolever system with a central driveshaft and 110 mm (4.3 in) of travel, which minimized torque reactions during acceleration; later models adopted the improved Paralever setup, adding a second pivot arm for even greater stability under load. The low center of gravity, resulting from the engine's forward longitudinal orientation, further aided the suspension in delivering predictable dynamics for extended rides. Braking was handled by dual 285 mm front disc brakes paired with two-piston calipers, complemented by a single 285 mm rear disc with a one-piston caliper, offering progressive and reliable stopping power suited to the bike's touring intent. An optional (ABS), developed in collaboration with Bosch, became available starting with 1988 models, marking one of the earliest implementations on a production and enhancing safety in wet or emergency conditions. The K100's wet weight was 249 kg (549 lb), which the braking setup managed effectively without compromising maneuverability.

Dimensions and Performance

The BMW K100 measures 2220 mm (87.4 in) in overall length, with an overall height of 1155 mm (45.5 in) and a seat height of 810 mm (31.9 in). Its fuel tank capacity is 22 liters (5.8 US gallons), providing sufficient range for long-distance touring. The wet weight is approximately 249 kg (549 lb), contributing to its substantial road presence while maintaining balance for sport-touring duties. In terms of performance, the K100 achieves a top speed of around 135 mph (217 km/h), with acceleration from taking approximately 4.1 seconds. Fuel economy typically ranges from 45 to 55 , depending on riding conditions and model variant. The shaft drive system promotes neutral characteristics, ensuring stable handling at highway speeds and responsive behavior in corners. Compared to the K75 variant, the K100 is heavier by approximately 12-20 kg (26-44 lb) depending on the specific variants compared, with a slightly higher top speed of 130-135 mph versus the K75's 125 mph. The K75 offers improved at 50-60 due to its smaller three-cylinder engine, while both models exhibit similar stable dynamics aided by the brake system's progressive feel.

Production and Reception

Manufacturing and Sales Figures

The BMW K100 family was primarily manufactured at the plant in , , which has been the dedicated facility for production since and served as the central hub for the K-series inline-four models from their inception through 1992. While the majority of assembly occurred in , select components for the U.S. market were occasionally handled through local distribution adaptations, though full production remained centralized in . Production of the K100 began with its public unveiling in 1983 at the Motorcycle Show, marking BMW's shift to liquid-cooled inline-four engines and initiating a new era for the brand's touring motorcycles. The base K100 model entered full production shortly thereafter, followed by variants like the K100RS in 1984, K100RT in 1984, and K100LT in 1986; the related K75 three-cylinder model joined the lineup in 1985 to offer a more accessible entry point. Sales peaked in the mid-to-late within the large-displacement touring segment, reflecting strong demand for the innovative shaft-drive, liquid-cooled designs amid a competitive market dominated by Japanese manufacturers. Over the production run from 1983 to 1992, BMW manufactured approximately 84,909 units of the K100 family, excluding the K75, providing a breakdown that highlights the popularity of sport-touring variants. The K100RS proved the most successful, with 34,804 units produced, followed by the K100RT at 22,335 units, the luxury K100LT at 14,899 units, and the base K100 at 12,871 units. Including the K75 series, which added over 50,000 units through 1995, the broader K-family exceeded 130,000 total motorcycles, underscoring BMW's commitment to the platform despite initial development challenges. The K100 family found its strongest markets in and the , where it appealed to riders seeking reliable long-distance touring options, with exports reaching numerous countries worldwide to capitalize on BMW's growing international presence. In the U.S., the base K100 retailed for over $5,300 in 1984, positioning it as a premium alternative to competitors like the and Kawasaki GPZ, though higher tariffs and import logistics influenced final pricing. Economically, the K100 series played a pivotal role in BMW Motorrad's recovery from a mid-1980s sales dip, where the brand's traditional air-cooled boxers had lost ground to lighter Japanese sportbikes; by the late 1980s, the K-models boosted overall revenues and stabilized the division amid broader industry shifts. This resurgence contributed to 's expanded global footprint, coinciding with a 25% increase in group revenues by 1988.

Market Reception and Reliability

Upon its launch in 1983, the BMW K100 received praise from contemporary reviewers for its innovative engineering and smooth power delivery, marking a significant departure from BMW's traditional boxer engines. Cycle World described the inline-four as a "four like no other," highlighting its quick-revving nature, solid 90 horsepower output, and the light, simple shaft drive system that minimized reactions for enhanced stability. The motorcycle's liquid-cooled design and Bosch LE-Jetronic were lauded for providing refined performance suitable for long-distance touring, positioning it as a competitive alternative to Japanese multis. However, initial reception was tempered by criticisms of its weight—around 510 pounds dry—and high cost, exceeding $5,300 for the base model, which made it less accessible compared to lighter, more affordable Japanese rivals like the or Yamaha Venture. Reliability in early K100 models was mixed, with owners and mechanics reporting frequent failures due to or low-fuel operation, as well as glitches in the that could cause intermittent stalling or poor idling. These issues stemmed from the complexity of the integrated fuel and ignition systems, often exacerbated by improper or prolonged storage. Later iterations, particularly from onward with the introduction of optional ABS, improved overall braking confidence but added weight (about 11 kg) and electronic complexity, potentially increasing repair demands. Despite these early teething problems, the K100 demonstrated strong long-term durability, with many examples achieving over 100,000 miles when spline lubrication, final drive oil changes, and regular valve adjustments were performed as recommended. The cylinder bores contributed to exceptional engine longevity, often outlasting 100,000 miles with minimal wear. The K100 found favor among touring enthusiasts for its stable highway manners and comfortable ergonomics, enabling effortless cruising at speeds over 80 mph with minimal vibration after the initial models' refinements. riders, however, often complained about its 500-plus-pound curb weight and low ground clearance, limiting off-road suitability despite its shaft drive's low-maintenance appeal. Sales in the were notably boosted by European police contracts, particularly for the faired K100LT variant used by forces like London's from 1986 to 1991, valuing its speed (up to 133 mph) and reliability for escort duties. Updates in refined the EFI with improved injectors and , addressing early fueling inconsistencies and enhancing response without the carburetion woes seen in some prior designs. Common owner fixes included routine final drive oil changes every 12,000 miles to prevent seal leaks and spline greasing to avoid drivetrain wear.

Legacy and Later Evolutions

The BMW K100's direct successors, the K1100 series produced from 1992 to 2001, built upon its foundational design with an enlarged 1,085 cc inline-four engine delivering between 85 and 125 horsepower across variants like the K1100RS and K1100LT, while introducing refined ABS as a standard feature on models from onward for enhanced braking stability. This evolution culminated in the transition to the K1200 lineup in 1997, which further refined the layout and shaft-drive system for touring applications. Key innovations from the K100, such as its mounting for a low center of gravity, were carried forward into later models, notably influencing the F800 series' parallel-twin configuration that maintained this orientation for balanced handling. Additionally, the K100's liquid cooling and shaft drive became enduring staples in 's motorcycle engineering, appearing in subsequent K-series and beyond to ensure reliability and smooth power delivery in high-performance and touring bikes. In 2025, the K100 endures as an affordable classic in enthusiast circles, with well-maintained examples typically valued between $1,000 and $5,000 depending on condition and mileage, making it accessible for restoration projects. It remains popular for conversions, where its robust frame and engine attract custom builders seeking a distinctive inline-four platform. Active owner communities, including the BMW Motorcycle Owners of America (MOA) forum dedicated to "Flying Brick" K-bikes, foster ongoing support through technical discussions, parts sharing, and ride events. Culturally, the K100 has cemented its status as an engineering icon, earning the affectionate nickname "Flying Brick" for its blocky, reliable inline-four engine that symbolized BMW's bold shift to modern technology in the 1980s. It has appeared in films and enthusiast rallies, highlighting its role in popularizing advanced features like , while 2024 retrospectives praised its enduring boldness in motorcycle design history.

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