Abstract: A convertible motorcycle seat includes a backrest hinge assembly having a base plate secured to the rear portion of the platform, and an elongated pivotable arm having transversely spaced depending ears, a pivot member extending transversely of, and journalled in upstanding ears on the base plate. The pivotable arm is pivotable into an erect position extending generally vertically and into a collapsed position extending generally forwardly of the saddle. The depending ears have a cam surface including a pair of spaced recesses spaced arcuately about the pivot member with a convexly arcuate lobe therebetween. An indexing pin extends transversely of the base plate, and biasing means biases the indexing pin against the cam surfaces of the depending ears and into one of the recesses whereby the pivotable arm is firmly held in an erect position or in a collapsed position.