The problem of providing a rigid structure to an open-topped sports car was resolved by Barry Bilbie, Healey's chassis designer, who adapted the idea provided by the Jaguar D-type, with rear suspension forces routed through the bodyshell's floor pan. The Sprite's chassis design was the world's first volume-production sports car to use unitary construction, where the sheet metal body panels (apart from the bonnet) take many of the structural stresses. The original metal gauge (thickness of steel) of the rear structure specified by Bilbie was reduced by the Austin Design Office during prototype build, however during testing at MIRA (Motor Industry Research Association) distortion and deformation of the rear structure occurred and the original specification was reinstated. The two front chassis legs projecting forward from the passenger compartment mean the shell is not a full monocoque. The front sheet-metal assembly, including the bonnet (hood) and wings, was a one-piece unit, hinged from the back, that swung up to allow access to the engine compartment.