I'm just curious. Penny-farthings look uncomfortable and difficult to ride. They also seem very dangerous for a multitude of reasons. I'm not sure when they were manufactured/popular to ride in comparison with a standard safety bicycle or a velocipede.
But under what circumstances does this seem useful? What is the reasoning behind the front wheel - is it a pedaling ratio or something?
What is the reasoning behind the front wheel - is it a pedaling ratio or something?
Pedal ratio is part of it, but not the whole story. The earliest pedal-powered bicycles, appearing in about 1867, generally used direct drive - pedals attached to the axle of the front wheel. These were heavy bicycles! Their frames were solid bars of wrought iron, or sometimes even heavier cast iron (heavier because it needed to be thicker - these bicycles could weigh 30-40kg) and the wheels were built like wagon wheel, with a wooden rim, rigid wooden spokes, and an iron tyre to strengthen it. One example of such a bicycle:
Note that on this example, the front wheel is larger than the rear wheel. This was to provide a better pedal ratio, and also to provide a slightly smoother ride. Roads were typically rough, and the wooden wheels with iron tyres transmitted the shock of those bumps to the rider. Not for nothing were these machines nicknamed the "boneshaker".
In principle, the boneshaker could have been scaled up to have a front wheel of penny-farthing size. This would have resulted in a terrible bicycle - it would have been very heavy. This style of wheel is heavy, and it grows even heavier as you make it larger. In particular, the spokes need to be thicker for lateral strength. In 1868, Eugène Meyer developed a lightweight wheel, the forerunner of the modern bicycle wheel. It was an all-metal wheel, and much lighter than the older style. The key innovation was thin wire spokes under tension. In the old style of wheel, the spokes below the axle supported the axle, under compression like pillars. In Meyer's wheel, the axle hung from the upper rim, supported by tension like a suspension bridge. The spokes no longer needed to be thick to avoid bending, since they were always under tension. Soon, a solid rubber tyre was added. An early Meyer bicycle with his new lightweight wheel:
Now, the front wheel could grow larger without the bicycle becoming too heavy, and the penny-farthing quickly developed, reaching its classic form in 1871. Over the next decade or so, new innovations appeared, such as lighter frames made from hollow steel tubing, and sprung seats.
The penny-farthing was not a perfect bicycle. The high seat of the rider made it unstable, and it could tip over forwards when going downhill.
A large front wheel was not the only way to obtain a better pedal ratio. If the back wheel could driven, then the tipping-over forward problem would be solved. However, since the rider could sit behind the rear axle, something other direct drive was needed. The usual solution was treadle drive, where the pedals were both ahead of the rear axle, connected by levers which drove the wheel using a ratchet mechanism or by connecting to cranks. A variety of methods were used. With short levers, the rider had to sit above the rear wheel, which still resulted in an unstable ride:
This solved the tipping-over forward problem:
but replaced it with a tipping-over backward problem. The new bicycle was safer to ride downhill, but more dangerous to ride downhill.
Longer levers connecting the pedals to the large rear wheel let the rider sit lower, in front of the rear wheel. This was more stable, but the bicycle was longer and heavier.
Geared indirect drive would allow the use of smaller wheels while still providing a good pedal ratio. A variety of methods were already known, such as drive belts, drive chains, and geared driveshafts. All had been used to transmit power to machinery. There were some difficulties making them work well for bicycles:
They added weight, and making lighter versions required better engineering and higher-precision manufacturing, and therefore cost.
These systems were lossy. Friction, stretching of drive belts, etc. robbed the rider of some of his or her effort. Again, better engineering and higher-precision manufacturing, and higher cost could improve things.
Direct drive, such as on the boneshaker and the penny-farthing, was more reliable. Fewer moving parts meant fewer things could go wrong.
The drive belts of the time were simple smooth belts, and depended on friction. Belt tension needed to be very high for them to work well, especially at low speeds. Belts dropped out as a serious contender (but would make a comeback in the 1970s, in the form of toothed belts which didn't need high tension). Driveshafts were more reliable than chains (in part because they could be better protected from dust and mud), but heavier and more expensive. In the end, chain drive won (but driveshafts continued to be used occasionally over the next decades).
The penny-farthing still had the advantage of a smoother ride. However, the pneumatic tyre of 1888 (i.e., air-filled rather than solid rubber) allowed smaller wheel to provide a smooth enough ride. As the engineering problems with indirect drive were solved, the stage was set for the modern style of bicycle: equal-sized wheels, with the rear wheel driven by a chain. This was the "safety bicycle", so named for its improved stability compared to the penny-farthing. The first "safety bicycle" to carry that name appeared in 1876, but the type existed earlier - these were the bicycles that motivated improvement of indirect drive systems. As drive systems became lighter and more reliable, and the pneumatic tyre was introduced, the "safety bicycle" became more and more popular, driving the penny-farthing (which was still a more reliable machine) into obsolescence. This took time - the penny-farthing continued to be produced into the early 1890s, surviving competition from the safety bicycle for over 15 years.
The story of early bicycle engineering is a tale of engineering to make parts stronger and light, and precision engineering for better drive trains. In these respects, the bicycle was much like the lightweight spoked-wheel war chariot of more than 3,000 years earlier. Light weight and strength, coupled with precision manufacturing, were also the key elements that would soon allow successful heavier-than-air powered flight. Notable, the Wright brothers started in the bicycle business, first selling and repairing them, and then moving into manufacture. After the Wright brothers flew, and the airplane replaced the bicycle as cutting-edge engineering, other bicycle mechanics, engineers, and manufacturers moved into the aircraft industry.
For lots and lots on the history of bicycle engineering, see
