Since my primary unicycle broke last weekend (see my race report), I am looking at options for a replacement. This seems a good opportunity to provide a brief write-up on the pros and cons of various wheel sizes, as they pertain to unicycling at least. In general, larger wheels are more difficult to start riding, since they roll further and are more sensitive to pedal input. On the other hand, they move faster (due to afore-mentioned larger roll-out), so are more suitable for longer trips.
20″ (and 19″) unicycles are often the first that people try. The smaller wheel size makes them more suitable for learning on (I learned on a 20″ borrowed from a friend). They are also the ride of choice for trials and flatland, where the generally higher control (due to low roll-out) that can be attained is desirable. They are also popular for hockey or polo.
24″ unicycles were for a long time the standard. They are still popular for freestyle riding and hockey/polo. They are also often used for very technical downhill MUni.
Relatively recent, but becoming very popular due to a couple reasons: a) there are a huge number of tyre choices, since it is the standard for bicycles; b) they are better for longer rides than 24″ wheels. No one I know of is really using these for anything other than MUni though.
This is an excellent choice for longer cross-country rides. The larger wheel eats up the kilometres and still allows enough control that you can ride reasonably technical terrain. This is becoming a popular bike size as well, so tyre choices are constantly improving.
Yes, a wheel nearly a metre in diameter. The size of choice for distance riding, especially on road, these are what long-distance tours and races like the Cape Argus (biggest individually timed bike race in the world. It also has a unicycle category) are usually done on. Many people who regularly commute using a unicycle (yes, there are a fair few) use a 36″, especially if the distance is a bit greater. The jump to learning to ride one of these beasts is bigger than to ride a 29″, but the difference in speed is notable, and generally thought worth it. They are also a trifle harder to store. In theory, a 36″ wheel is weaker, so caution using them in rough terrain is required.
Other sizes are available and have been tried. 12″ or 16″ wheels are sometimes suggested for younger children to learn on. Wheels bigger than 36″ exist, but tend to be custom-made. There is some interest in a 32″ wheel, which would bridge the gap between 29″ and 36″ nicely.
Handle-bars are available (and can be home-made easily enough). These allow for more comfort on longer rides, since the bar can take some of the weight, rather than just the saddle. Brakes are also becoming increasingly common, with disc brakes being the latest thing. These are usually used to control ones’ speed on long or steep downhills. Since unicycles are fix-geared, in order to slow down on hills one needs to put pressure on the back pedal which can get tiring on long downhills. The brakes help alleviate this. Brakes are not used to stop though.
Hopefully this is of use to someone, somewhere. Feel free to e-mail me or send me a message on Twitter (@astonsplat) should you have any comments on this.