What type of chassis is the original Lotus Elan noted for using?

The original Lotus Elan is noted for using a steel backbone chassis.

Lotus built the first-generation Elan around a fabricated mild-steel backbone chassis, with a fiberglass body bolted over it. The central structure resembled a double-ended tuning fork: its front and rear sections carried the engine, suspension and differential, while the narrow central backbone provided the principal structural strength.

This arrangement reflected founder Colin Chapman’s famous emphasis on low weight. The Elan weighed far less than many contemporary sports cars, yet its chassis delivered useful bending and torsional rigidity. The fiberglass body also resisted corrosion better than a steel body, although the steel chassis itself could rust and often required replacement.

The backbone design should not be confused with a monocoque, in which the body shell carries most structural loads, or a ladder frame, which uses two long parallel rails. Lotus reused the basic backbone concept in later cars, including the Europa. The original Elan was produced from 1962 to 1975 and became celebrated for its precise steering, independent suspension and lightweight construction.