BMW K75

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BMW K75
Blue BMW K75 fitted with topbox, parked in a pedestrian area
1993 BMW K73
Manufacturer BMW
Production 1985–1995
Assembly Germany
Successor BMW K1100
Class Standard
Engine Longitudinal DOHC I3, 740 cc (45 cu in)[1]
Bore / stroke 67 mm × 70 mm (2.6 in × 2.8 in)[1]
Compression ratio 11.0:1[2]
10.5:1[1]
Top speed 131 mph (211 km/h)[citation needed]
Power 75 hp (56 kW) @ 8000 rpm[citation needed]
Torque 50 lb·ft (68 N·m) @ 6000 rpm[citation needed]
Ignition type Bosch L-Jetronic[1]
Transmission 5-speed foot shift,[1] shaft drive
Frame type Tubular steel, open cradle with engine as stressed member
Suspension Telescopic forks,[1] single-sided swingarm
Brakes Dual front discs and single rear disc,[1] or rear drum
Rake, trail 27.5°/3.98 in (10.1 cm)
Wheelbase 59.7 in (152 cm)[1]
Dimensions L: 87.4 in (222 cm)
W: 35.4 in (90 cm)
H: 51.2 in (130 cm)
Seat height 31.9 in (81 cm)[1]
29.9 in (76 cm) (low seat)
Weight 505 lb (229 kg) (dry)
536 lb (243 kg) (wet)
Fuel capacity 5.54 US gal (21.0 l)
Fuel consumption 59 mpg-US (4.0 l/100 km)
Related BMW K100
BMW K1

The BMW K75 is a standard motorcycle produced by BMW Motorrad from 1985 to 1995. At the time of its introduction, the K75 was BMW's least expensive motorcycle.

Model designations[edit]

Various models of the K75 were produced:

  • 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
  • K75C—with a small 'cockpit' fairing mounted to the handlebar[3]
  • K75S—with sports fixed fairing, stiffer suspension and lower and narrower handlebars[4]
  • K75RT—with full fairing for 'road touring'[5]
Red BMW K75S with topbox and panniers, parked on a city street.
K75S with belly pan and touring bags

The S and RT versions have a rear disc brake and 17 inch rear wheels, whereas the others have a single leading shoe drum brake and 18 inch 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 or lowered. Some taller riders complained of wind buffeting with the smaller S model stock windscreens.[citation needed]

Engine and transmission[edit]

All K75 models share the same drivetrain. They are powered by a 740 cc liquid-cooled inline three-cylinder engine[5] with Bosch LE Jetronic fuel injection.[6] 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). They have a five-speed transmission with a dry clutch and a shaft-driven final drive. The engine is oriented longitudinally and horizontally to lower the center of gravity and allow the most efficient power transfer to the shaft drive.

Background to K75 launch and design[edit]

Black BMW K75T with topbox and panniers, parked on a driveway in front of a house and metal gates
1987 BMW K75T

The K-series lineup, including the K75 and K100, were not just new models; these designs were radical departures from almost every aspect of previous BMW offerings. The K-bikes introduced new technology and refinement to a premium brand. At the time, BMW and Harley-Davidson were the only major manufactures 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.

The K75 was planned alongside the K100; the introduction of the K100 before the K75 was a marketing strategy. As a result, the design for the K100 engine provided for the balance shaft used in the K75. The K100's water pump's drive shaft was designed to run at a ratio of 1:1; the correct speed for the balance shaft on an inline-three engine. On the K75, balance weights were added to the shaft, turning it into a balance shaft.[2] The balance shaft made the K75's engine smoother than the K100's engine.[2][7] The K75 engine uses a crankshaft with 120° between the throws.[8][9]

The K75 frame differs from the K100 frame only in the positioning of the front engine mounts further back in the frame to accommodate the shorter engine and in the angle of the downtubes. The K75 had the same wheelbase, seat height, and steering geometry as the K100. The radiator and fuel tank were also smaller than those on the K100.[2]

The K-series offered refinements such as computer-controlled fuel injection,[6] all stainless steel exhaust, rust-free aluminum fuel tank, anti-lock brakes on later models, mono-lever in the rear and single shock absorber, adjustable headlight, high capacity 460 watt alternator, electrical accessory plug-in, and self-canceling signal lights. The engine design had excellent vibration isolation with an internal counter rotating shaft. 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).

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.[1] For 1995 anti-lock braking was standard on the K75S.[10]

Notes[edit]

  1. ^ a b c d e f g h i j Boehm 1995, p. 36.
  2. ^ a b c d Anderson 1985, p. 76.
  3. ^ Anderson 1985, pp. 76-77.
  4. ^ Dean 1986, p. 43.
  5. ^ a b Thompson 1993, p. 31.
  6. ^ a b Wade 2004, p. 109.
  7. ^ Millch 2008, p. 29.
  8. ^ Anderson 1985, p. 77.
  9. ^ Cathcart 1985, p. 25.
  10. ^ Boehm 1995, p. 39.

References[edit]

External links[edit]