Historical materials for automotive steering wheels: Considering rigidity, finish, and moldability used in classic automotive interiors, steering wheels have commonly been manufactured from which of the following plastics?

Introduction / Context:
Automotive steering wheels historically needed a hard, glossy, and moldable material capable of fine surface finish. Earlier generations often relied on specific cellulose-based plastics before the widespread adoption of modern engineering polymers and polyurethane overmolding.

Given Data / Assumptions:

• Focus on traditional/legacy materials used in classic vehicles.
• Properties sought: good moldability, surface finish, sufficient rigidity.

Concept / Approach:
Cellulose acetate was widely used for molded consumer goods and interior automotive trim owing to its machinability and finish. Cellulose nitrate (nitrocellulose) is flammable and less suitable for safety reasons. PVC and HDPE are useful plastics but have different tactile and mechanical profiles and were not the classic choice for hard steering wheels in earlier eras.

Step-by-Step Solution:
Match historical manufacturing practice to material properties.Eliminate hazardous or unsuitable options (cellulose nitrate).Recognize cellulose acetate as a period-appropriate, commonly used steering wheel plastic.

Verification / Alternative check:
Restoration guides and period catalogs list cellulose acetate and phenolic (Bakelite) as common materials; among the provided options, cellulose acetate is the most fitting.

Why Other Options Are Wrong:

• Cellulose nitrate: safety/flammability concerns.
• PVC: used for skins and flexible parts; not typical for hard wheels historically.
• HDPE: waxy surface, limited stiffness and finish compared with acetate/phenolics.

Common Pitfalls:

• Assuming modern polyurethane overmolding was always the standard.
• Confusing trim skins (PVC) with the rigid core material.

Final Answer:
cellulose acetate