Trials, Street and Flatland Unicycles
by John Foss
A trials unicycle is specifically made for hopping and riding over obstacles and not necessarily for getting from place to place. Wheel sizes are 19" and 20" because a smaller wheel is lighter and more maneuverable. Because of the constant pounding a Trials unicycle endures, it must have a very strong axle and crank set. A fat tire completes the trials image for a cycle with lots of bounce for those hops and drops.
The trials format is also a great off-road unicycle for a younger or smaller rider. A small child can bounce all over the place on a fat 20" wheel, while not being bogged down by a cycle that's too comfortable fit.
For Street riding (the competitive event or just for fun) the requirements are basically the same. You still need to jump high, land hard and be able to move quickly. Street also adds the element of doing tricks, so look for a frame you can put your feet on.
Flatland, which is like Street but without the obstacles, can be done with a Trials unicycle, a Freestyle unicycle or something in between. It's a relatively new area of riding and there isn't as of yet a solid recommendation for what type of equipment is best.
If you are shopping for a Trials unicycle, read the Rough Terrain Unicycles article for some more background on what you need to know about these beasts.