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Monocoque: The body of the car provides all of the strength through distributing loads through its "skin". This is a design typically only seen in aircraft, F1 motorsports, and some high performance motorcycles, where the entire body of the vehicle is formed with a strong shell made of either carbon fibre composites or aluminum panels. It has the Some high performance consumer cars use a monocoque for the passenger cell but extend metal subframes from the front and back for mounting the engine and suspension. Monocoques have the advantage of theoretically achieving the greatest strength-to-weight ratio, but is are very hard to design because stretched-skin structures are difficult both to simulate and changemodify.
Solar Car Frames
Solar cars can be found that use steel space frames and composite unibodies. Composite unibodies can be formed by building a strong composite chassis using thick composite panels and attaching to it a shell made of thinner composite material. The differences between Challenger and Cruiser class vehicles become relevant here: for example, Cruiser class vehicles must incorporate a much larger passenger cell which can made designing a strong composite frame difficult. Furthermore, all solar cars must have a metal roll cage, which can potentially be challenging to attach reliably to a composite frame.
Midnight Sun's MSX was designed with a steel space frame, whereas MSXI was designed using a carbon fibre monocoque.