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A motorcycle frame includes the head tube that holds the front fork and allows it to pivot. Some motorcycles include the engine as a load-bearing, stressed member. The rear suspension is an integral component in the design. Traditionally frames have been steel, but titanium, aluminium, magnesium, and carbon-fibre, along with composites of these materials, have been used. Because of different motorcycles' varying needs of cost, complexity, weight distribution, stiffness, power output and speed, there is no single ideal frame design.[1]


Frame materialsEdit

SteelEdit

Triton Norton-Triumph motorcycle with polished frame and tank

Norton Featherbed frame in a Triton.

Examples

AluminiumEdit

Examples

Aluminium and carbon-fibreEdit

Examples
  • Bimota SB8K (composed of two aluminium alloy beams and carbon fibre plates)

Carbon fibreEdit

TitaniumEdit

Examples

MagnesiumEdit

Elf5

Elf 5 at the Honda Collection Hall

Examples

Magnesium and aluminiumEdit

Examples

Frame TypesEdit

Pressed frameEdit

The frame is mass-produced by sheet metal pressed or stamped into shape. Typically a single-cradle structure is used.

Examples

Single cradleEdit

The motorcycle engine is held in a single cradle with a single spine.

Half-duplex cradle frameEdit

The motorcycle engine is held in a double cradle with a single spine and single downtube.

Examples

Full duplex cradle frameEdit

The motorcycle engine is held in a full by two separate cradles, normally with a single spine.

Examples
Honda CB750a

Double cradle frame on Honda CB750

Double cradle or perimeter frameEdit

Two cradles follow the perimeter

Examples

Spine or backbone frameEdit

The motorcycle engine is suspended from a single spine.

Examples


2011 Kawasaki ZX10-R below airbox.jpg
Frame of a 2011 Kawasaki ZX-10R.
Buell Lightning XB9SX CityX.jpg
Aluminum beam frame on Buell Lightning.

BeamEdit

Twin beams join headstock to swingarm pivot in as straight and short a line as possible.

Examples

MonocoqueEdit

Main article: Monocoque

Supports structural load using the external skin of the frame.

Biella-MP5 Piaggio Paperino

1944 Piaggio MP5 monocoque chassis.

Examples


S2R1000-101 v2 1024 web

Steel trellis frame (red) on a Ducati Monster 1000. The engine is a stressed member.

TrellisEdit

Similar to the beam frame, connecting the steering head and swingarm pivot point directly as possible. The frame is made up of a large number of short steel (or aluminium) tubes welded together to form a trellis.

Examples

Engine as a stressed memberEdit

For rider comfort, a motorcycle's engine can be mounted on rubber bushings to isolate vibration from the rest of the machine. This strategy means the engine contributes little to frame stiffness, and absorbing rather than dissipating vibration can lead to stress damage to the frame, exhaust pipes, and other parts.[1]

Instead, if the engine is rigidly mounted to the frame, vibrations pass to and are dissipated via the whole frame, and the rider. Rigid mounting allows the engine to contribute to the overall stiffness of the frame. It also becomes possible to mount the swingarm directly to the engine rather than the frame, avoiding the need for frame members extending downward to the swingarm pivot. By increasing the number of mounting points between the engine and frame, vibrations and stress can be better dissipated in the frame, typically creating a triangle between the swingarm in the rear, the cylinder head at the top and the lower crankcase area at the front. If a rigidly mounted engine not only contributes to, but is critical to, the stiffness of the frame, and is an integral part of closing the triangle or trellis structure that transfers force from the headstock to the swingarm, to the point that without the engine the frame would be deformed, the engine is called a stressed member, or a lifted engine. Sharing the load between the engine and frame reduces the overall weight of the motorcycle.[1]

During early testing of the 1983 Kawasaki GPZ900R, twin downtubes were included, creating a full cradle, but the downtubes were found to carry little load, so they were removed, relying entirely on the combination of the steel backbone and engine for chassis rigidity.[4] BMW's R1100 series twins of 1994 relieved the frame of stress entirely, with the engine carrying the total load from the front Telever fork to the rear Monolever.[5][6]

See alsoEdit

References / sourcesEdit

External linksEdit

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