Tuesday, February 8, 2011

Engineering advance #9: Alloy beam frame

Nearly 30 years later, Cobas' designs still look the business. This KTM 'crosser motor probably didn't lend itself to use as a fully stressed member, hence the fairly stout 'downtubes'. But conceptually, it's basically the same frame now used by almost every sportbike manufacturer except Ducati (and, appropriately, KTM.)
Most modern motorcycles feature a beam frame that connects the steering head to the swingarm pivot in a nearly straight line. This stiff, light design sprang from the imagination of an influential Spanish engineer named Antonio Cobas. In 1983 his JJ Kobas 250cc Grand Prix racer was the first bike with such a frame. It was quickly copied by other Grand Prix racing teams and then into streetbike frames, such as the first Yamaha “Deltabox” chassis which first appeared on the manic TZR250 repli-racer in 1985.

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