how fast does the big wheel move
They can pedal faster or they can have a bigger wheel. Even for sporty people, about 100 turns a minute is the limit to how fast they can turn the pedals. A typical bicycle might have a wheel of 0.7 m, but the penny-farthing often had a front wheel of 1.5 metres (about 1.6 yards). 1 turn of the pedals moves the bicycle 3.142 x 1.5 metres forward, i.e. 4.7 metres.