Product Code Database
A motorcycle frame is a motorcycle's core structure. It supports the engine, provides a location for the steering and rear suspension, and supports the rider and any passenger or luggage. Also attached to the frame are the fuel tank and battery. At the front of the frame is found the steering head tube that holds the Swivel Motorcycle fork, while at the rear there is a hinge for the swingarm suspension motion. Some motorcyclesNote: ... such as the Ducati 900 SS include the engine as a load-bearing stressed member; while some other bikes do not use a single frame, but instead have a front and a rear subframe attached to the engine.Note: An example is the Vincent HRD
Examples
Antonio Cobas is credited with pioneering the modern, aluminum perimeter frame chassis now used on many modern racing and production motorcycles. In 1982, Cobas developed a stronger and lighter aluminum twin-beam chassis to replace the steel backbone frames. The technology was copied by major motorcycle manufacturers and by the 1990s, all the major racing teams in Grand Prix competition used the aluminum frame design pioneered by Cobas.
French industrialist and engineer Georges Roy attempted in the 1920s to improve on the bicycle-inspired motorcycle frames of the day, which lacked rigidity. This limited their handling and therefore performance. He applied for a patent in 1926, and at the 1929 Paris Automotive Show unveiled his new motorcycle, the Art-Deco styled 1930 Majestic. Its new type of monocoque body solved the problems he had addressed, and along with better rigidity it did double-duty, as frame and bodywork provided some protection from the elements. Strictly considered, it was more of a semi-monocoque, as it used a box-section, pressed-steel frame with twin side rails riveted together via crossmembers, along with floor pans and rear and front bulkheads. name=french>
A Piatti scooter light scooter was produced in the 1950s using a monocoque hollow shell of sheet-steel pressings welded together, into which the engine and transmission were installed from underneath. The machine could be tipped onto its side, resting on the bolt-on footboards for mechanical access. The Motor Cycle, two-page road test, 7 March 1957, pp.298-299. Accessed 15 June 2019
A monocoque-framed motorcycle was developed by Spanish manufacturer Ossa for the 1967 Grand Prix motorcycle racing season. Although the single-cylinder Ossa had less than its rivals, it was lighter and its monocoque frame was much stiffer than conventional motorcycle frames, giving it superior agility on the racetrack. Ossa won four Grands Prix races with the monocoque bike before their rider died after a crash during the 250 cc event at the 1970 Isle of Man TT, causing the Ossa factory to withdraw from Grand Prix competition.
Notable designers such as Eric Offenstadt and Dan Hanebrink created unique monocoque designs for racing in the early 1970s. The F750 event at the 1973 Isle of Man TT races was won by Peter Williams on the monocoque-framed John Player Special that he helped to design based on Norton Commando. F750 race result iomtt.com. Retrieved 27 December 2019 Honda also experimented with the NR500, a monocoque Grand Prix racing motorcycle in 1979. The bike had other innovative features, including an engine with oval shaped cylinders, and eventually succumbed to the problems associated with attempting to develop too many new technologies at once. In 1987 John Britten developed the Aero-D One, featuring a composite monocoque chassis that weighed only .
An aluminium monocoque frame was used for the first time on a mass-produced motorcycle from 2000 on Kawasaki's ZX-12R, their flagship production sportbike aimed at being the fastest production motorcycle. It was described by Cycle World in 2000 as a "monocoque backbone...a single large diameter beam" and "Fabricated from a combination of castings and sheet-metal stampings".
Single-piece carbon fiber are sometimes described as monocoques; however as most use components to form a frame structure (even if molded in a single piece),, Velocite-bikes.com these are frames not monocoques, and the pedal-cycle industry continues to refer to them as framesets.
Some motorcycles, such as the Yamaha TRX850, have hybrid frames that employ alloy at the swingarm pivot area. Another variation is to suspend the engine from a trellis frame, but have the swingarm pivot cast into the rear of the engine.
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.
Stressed member engines were pioneered at least as early as the 1916 Harley-Davidson 8-valve racer, and incorporated in the production Harley-Davidson Model W by 1919. This was called a keystone, or diamond, frame. The 1946 Vincent Series B Rapide was designed with an advanced chassis, termed a "tour de force for its day," that included a stressed member engine. 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. BMW Motorrad's R1100 series twins of 1994 relieved the frame of stress entirely, with the engine carrying the total load from the front Telelever fork to the rear Monolever.
Modifying the stiffness of a factory-produced frame can be undertaken to improve handling characteristics. This is often done by triangulating the factory frame. Triangulation is a technique used in many engineering applications to stiffen structures. However doing so can also have undesirable effects if it overloads other parts of the frame, as a flexible frame acts as a spring to absorb some loads.
Lateral stiffness
In the 21st century, advances like high power engines driving high traction tires, and better-performing suspension components, especially forks, led to a situation where designs with increased overall frame stiffness were made available to consumers. Analysts differ on whether infinite lateral stiffness is desirable, or whether a finite degree of built-in flex is preferable.
Motorcycle frame measurement
If the handling of the motorcycle is not appropriate, it is important to check the deformation of the geometry of the motorcycle frame. This measurement can be important after an accident or before buying a used motorcycle.
See also
Sources
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