BMW K75 vs. BMW K100- Which one is for you?

Fans of classic motorcycles know the BMW K75 vs. BMW K100 debate. Which one is the best? Should you even prefer one over the other?

The BMW K series of bikes began with the K100 and later tricked down to the K75. The K75 is the smaller brother to the K100. It borrows a lot of features from the K100 with various downgrades on several elements. However, the K75 is its bike with more reliability than its predecessor. 

This article will focus on the similarities and differences between the BMW K75 and the BMW K100, informing you on what they are and what they have. We will focus on their specifications for each and how they match up against each other.

BMW K100

BMW K100

The BMW K100 came first. It is a family of 4-cylinder 987 cc motorcycles produced between 1982 and 1992. The model saved BMW’s motorcycle legacy, which had been dwindling for years. In the late 1970s, the company faced significant competition from Japanese manufacturers using new and advanced technology in their motorcycles. Moreover, BMW faced lots of challenges due to emissions regulations which demanded innovation and investment.

A BMW team comprising Karl Heinz Abe, Claus Luthe, and Klaus Volker Gervert designed the K100; thus, making BMW a significant player in the bike industry. The team opted for a four-cylinder engine dubbed the ‘K4’, which would later be modified to make the ‘K3’ used in BMW K75. The K100 featured a Bosch LE-Jetronic fuel injection system and a breaker-less electronic ignition system. The fuel injection system allowed for more power and decreased fuel consumption by primarily shutting off fuel under deceleration to 2000 rpm.

The engine design used allowed for easier access to the engine over other conventional techniques by implementing the crankshaft positioning to the right side of the bike. The cylinder head, injectors, camshafts, and spark plugs were positioned on the bike’s left side.

The K100 received several upgrades and modifications to make a couple of K100 variants:

  1. K100C – had an upgraded cockpit fairing connected to the handlebar.
  2. K100RS – also had an upgrade to the fairing that entailed sports fixed fairing and low-positioned handlebars.
  3. K100RT – introduced a full touring fairing.
  4. K100LT – came with a higher screen.
  5. K100TIC – introduced high output alternator, extra wiring harnesses, and taller gearing. This model was meant for emergency service sectors such as police, firefighters, ambulance, and military.

BMW K75

BMW K75

BMW decided to expand the K series in 1985 by introducing the K75. The K75 was made alongside the K100 but was launched years later due to marketing strategies. The engine type used in the K100 posed a few challenges for being long and heavy. The company decided to develop smaller engines to counter these issues, and this is how the K75 began. The four-cylinder engine model used in the K100 got stripped down by one cylinder to make the K75 engine a three-cylinder inline engine.

The goal of the K75 was to be smoother, reliable, shorter, and lighter while still being as powerful as it could be. The company increased the compression ratio for fuel efficiency, making the K75 more efficient than the K100. A lot of problems that appeared in the K100 never appeared in the K75.

The K75 received several upgrades and modifications to make a couple of K75 variants:

  1. K75T – contained touring bags, a rear top case, and engine crash bars.
  2. K75C – had an upgraded cockpit fairing connected to the handlebar.
  3. K75S – had a better and stiffer suspension system, a sports fairing, and smaller handlebars.
  4. K75RT – introduced a full touring fairing.

Overview Comparison of BMW K100 and BMW K75

Design comparison

The K series bikes have more similarities than differences when it comes to exterior design. Alterations and variants of the original/naked BMW K100 or BMW K75 and similar modifications and upgrades. The bare K100 had no fairing and did not attract much attention in aesthetics, leading to K100C, K100Rs, K100RT, and K100LT. 

The K100C got modified with the introduction of a narrow cockpit fairing attached to the handlebar. They added sports fairing to make the K100RS that also had shorter handlebars. K100RT featured one mod: the use of an entire touring fairing, while, in 1986, the K100LT was added to the list with a taller screen and extra equipment (radio kit, comfort seat, and top case) for luxury touring. The best-seller among all of these was the K100RS which provided a beautiful and helpful fairing. It enabled better weather protection and high-speed wind deflection due to the spoiler used.

The K75 went through similar design alterations as the K100 apart from the production of an LT or TIC version replaced with a T version, the K75T.

The two models, K100 and K75, have similar frames, wheelbase, steering geometry, and seat height. Their specifications and dimensions are so identical that around 80% of their components are interchangeable. However, a few differences can be noticed, such as the placement of the front engine mounts and the use of smaller radiators and fuel tanks. In the K100, the front engine mounts are positioned a little bit forward than in the K75. Moreover, the down tubes are positioned at different angles in the two models.

Main Differences

A significant difference exists in power produced. The K100 has more power than the K75; but, the K75 is more streamlined and smoother, thereby providing a more comfortable experience, especially at speeds obtained above 4000 rpm. K100 has a maximum power of 90 horsepower / 65.6 KW at 8000 rpm, while the K75 comes with the full power of 75 horsepower / 55KW at 8500 rpm.

Since the K75 engine was smaller than the K100 engine, BMW had to make several adjustments to increase power. The engineers introduced an elongated valve timing, increased the compression ratio from 10.2: 1 to 11.0: 1, shortened the intake manifold, and returned the exhaust system. The K75 engine was made lighter than the K100 engine. It was made lighter by reducing the weight of the K75 to 236 kg instead of the 239 kg of the K100. 

Another difference in the BMW K75 vs BMW K100 battle is the type of engine they used. The machines are similar apart from one alteration, the number of cylinders. BMW K100 has four inline cylinders, while BMW K75 has three inline cylinders.

A few more modifications were made to the K75, including two counterweights in the take-off shaft to reduce vibrations, which plagued the BMW K100. Higher speeds, significantly above 90 kph or 120 kph, cause the K100 engine to vibrate. That is why the BMW K75 is more attractive to customers than the BMW K100.

With the difference in produced power, one can see how the K100 tops at 124.4 mph while the K75 has a maximum speed of 122 mph. The difference may be slight and less pronounced, but it is noticeable. The tuning of the engine performance enabled BMW to bring the acceleration of these two models closer. K100 can go from 0 – 100 kph in just 4.3 seconds, and the K75 does not trail behind with an acceleration of 0 – 100 kph in only 4.6 seconds.

Any Similarities?

BMW K75 and BMW K100 use engines with the same stroke (4 strokes) and bore (67 x 70 mm). Their cooling system is liquid (water) cooled, which is quite attractive system for most buyers. Nevertheless, they both use a 5-speed sequential manual transmission with a counter-rotating clutch, a shaft drive, and an electric starting system.

Engine Comparison

The engine used in K100 is a Dual Overhead Cam (DOHC) four-stroke engine with four horizontal inline cylinders and two valves per cylinder. Its capacity is rated at 987 cc, which is more than the 740 cc of the K75.

The K75 engine is a smaller engine modified from the K100 engine by striping one cylinder off. It is also a DOHC engine with three horizontal inline cylinders and two valves per cylinders like its predecessor.

Models Comparison

BMW K75BMW K100
K75T – contained touring bags, a rear top case, and engine crash bars.
K75C - had an upgraded cockpit fairing connected to the handlebar.
K75S – had a better and stiffer suspension system, a sports fairing, and smaller handlebars.
K75RT – introduced a full touring fairing.
K100C – had an upgraded cockpit fairing connected to the handlebar.
K100RS – also had an upgrade to the fairing that entailed sports fixed fairing and low-positioned handlebars.
K100RT – introduced a full touring fairing.
K100LT – came with a higher screen.
K100TIC – introduced high output alternator, extra wiring harnesses, and taller gearing. This model was meant for emergency service sectors such as police, firefighters, ambulance, and military.

K100 and K75 Specification Table

 BMW K75BMW K100
Production Year1985-19861982 – 1992
Engine4-stroke, horizontal 3 in-line cylinders, 2 valves per cylinder and DOHC4-stroke, horizontal 4 in-line cylinders, 2 valves per cylinder and DOHC
Power55 KW/ 75 horsepower at 8500 rpm – maximum power65.6 KW/ 90 horsepower at 8000 rpm – maximum power
Engine capacity740 cc987 cc
Compression ratio11: 110.2: 1
Max speed122 mph/196 kph 124.4 mph / 216.3 kph
Max torque50 ft lb. / 68 Nm at 6750 rpm63 ft lb. / 86 Nm
Transmission5-speed5-speed
Wheelbase59.7 inches / 1516 mm59.7 inches / 1516 mm
Front Brake2 x 285 mm diameter discs, 2 piston calipers2 x 285 mm diameter discs, 2 piston calipers
Rear brakeSingle 285 mm diameter discSingle 285 mm diameter disc, 1 piston caliper
Cooling systemLiquid coolingLiquid cooling
DriveShaftShaft
ClutchSingle dry plateSingle dry plate
Bore / stroke67 x 70 mm67 x 70 mm
Front tyre100/90 – 18 100/90 – 18
Rear tyre120/90 – 18 130/90 – 17
Fuel capacity5.54 US gal / 21 liters5.8 US gal / 22 liters
DimensionLength: 87.4 inches / 2220mm Height: 51.2 inches / 1300 mm Width: 35.4 inches / 900 mmLength: 87.4 inches / 2220mm Height: 45.5 inches / 1155 mm Width: 37.8 inches / 960 mm
Weight520 pounds / 236 kg527 pounds / 239 kg
Acceleration0 – 100 kph in 4.6 seconds0 – 100 kph in 4.3 seconds
Starting Electric Electric

Price Comparison

The cheapest motorcycle in the K series is the K75C which cost $7 293 when it came out. The bike now goes for a shocking $2,500 on various online bike shops, secondhand and refurbished, of course. The K75 and K75S follow it with an average price tag of $2,995 compared to the launching price of $5 950 in 1987—other alterations of the K75 cost more, with the K75RT being the most expensive at $4,700.

The BMW K100 lineup is more expensive and has the K100 as the cheapest with an average resell cost of $3000. The K100RS tops the chart with an average price of $3,995.

Conclusion

The K series bikes have left a considerable mark on the motorcycle industry with their designs, aesthetics, and functionalities, which have surpassed the test of time. They are a work of art and trusted daily drivers instead of being exhibition toys. More than 30 years later, the K100 and K75 are still attractive machines with incredible history and rich performance. 

The BMW K75 vs. BMW K100 deciding factors would be the smoothness at higher speeds, the maximum speed achieved, full power produced, and engine capacity. Regardless of choice, these two models are top-notch performers with incredible value.

Comments (2)

  1. po
    March 24, 2021
  2. John
    March 30, 2021

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