What engineering philosophy did internal hub gears generally prioritize over early derailleur designs?

Reliability and robustness for utility cycling.

During the early 1900s, engineers pursued two fundamentally different approaches to variable gearing: internal efficiency via the hub, or external simplicity and low weight via the derailleur. Internal hub solutions, like the Sturmey-Archer system, encased the gear mechanism within the rear hub shell. This protected the intricate moving parts from external elements like dirt, water, and impact, contributing to higher reliability and lower maintenance, making them the preferred choice for robust utility cycling. Conversely, derailleur systems, though potentially lighter, exposed their mechanisms and required significant refinement in areas like chain tensioning to achieve comparable reliability.