How did the safety bicycle retain speed potential compared to the Penny-Farthing?

By using mechanical advantage (gearing) instead of direct physical size

The engineering success of the safety bicycle was its ability to retain the high speed potential that the large wheel of the Penny-Farthing unlocked, but without the associated dangers. The Penny-Farthing achieved speed solely through the physical size of its wheel driving directly off the pedals. In contrast, the safety bicycle utilized the chain drive system, which acts as a form of mechanical advantage or gearing. This allowed the machine to deliver comparable or superior speed through efficient mechanical manipulation of pedal power transferred to the rear wheel, rather than depending on the impractical and dangerous requirement of an oversized driving wheel.