[lyons]

crash - there are two main reasons for high wheel bikes: Speed - Old-fashioned bikes didn’t use gears, so the only way to go faster was to have a bigger wheel. Since pedals were directly attached to the front wheel, the bigger the wheel, the further a single pedal push propelled you. In bike races, speed was a crucial advantage worth the absurd size.
Comfort - High wheel bikes were more dangerous, but they had advantages. Old roads were in poor condition, and the large wheel could roll over potholes and small rocks. It led to a smoother ride than smaller-wheel bikes, which were often called bone-shakers.
As for mounting an old-fashioned bike, The Wheelmen society has a useful guide. They write:
“It is much simpler than you think. On the lower part of the “backbone” (the part that goes down to the small wheel) there is a small step. The rider stands in back of the bike, with his hands holding the handlebar grips, with a foot up on the step. Pushing forward to get enough momentum to steer and balance (like a scooter), he steps up, settles into the seat, puts his feet on the pedals, and rides on.”

Link to the book: Illustrated Bicycle Primer

[crashryan]

Thanks for explaining this, Lyons! I hadn't thought of the relation between wheel diameter and bicycle speed.