The Unicyclopedia/Big wheels
Riding a big wheel, generally regarded as 29" and bigger, is generally fairly simple once you are up and riding. However, mounting can be significantly trickier, as you are sitting higher than on a smaller wheel. Big wheels make touring and distance riding a joy, and are graceful to look at.
This picture shows the custom-made Semcycle Big Wheel of Leo Vandewoestijne
Mounting Techniques (Always wear protection!)
The first thing to note is that the added mass of the wheel means that unless you have unusually strong legs, a rollback mount just isn't going to work at first. You probably won't be able to change the direction of the wheels rotation fast enough. That leaves two options, both of which are reasonably common - a static mount or a rolling mount. Bear in mind that in both cases, you will need to push off the ground somewhat harder than for a small wheel. For a static mount, some people find it helpful to bend forwards and hold the wheel, so they can pull themselves closer to the wheel after pushing off the ground. Some people find it easier to learn a rolling mount on a big wheel than on a small wheel.
Irregularities in the riding surface
Is there a bump in front of you? Don't worry! The advantage of a big wheel, other than speed, is that you barely notice bumps that you have to pay some attention to on a smaller wheel.
For stopping, there are two issues. The first is that there's more unicycle to stop, because it weighs more, and the second is that you're likely to be going faster. Despite these, the stopping techniques are the same as for a small wheel, it just takes longer so you need to plan ahead more. Using a hand brake helps in reducing speed as you get ready to step off. A brake also comes in handy in moderating your speed on down-hills.
Slowly, slowly. For idling, what matters is not how far you move the pedal but how far the wheel moves. When you idle a small wheel, moving the pedals between 45 degrees either side of vertical gets you about the right amount of wheel movement, but that kind of pedal movement will get you too much wheel movement on a larger wheel. Try to override your instinct to pedal back and forth automatically and instead react to the current state of the wheel. Again here, though, the weight of the wheel can be problematic, so don't expect to be able to idle a Coker easily (though Terry Peterson - the famed "Unigeezer" - has posted videos of himself idling a Coker).
At first you will want to leave plenty of room for turns. More lean may be required to get the big wheel banked over. As you get used to the big wheel, turns will come easier and less room will be required. 180 degree and hop turns are well within reason.
Most open speed and distance records are done on big wheels. 36" wheels have become popular due to the 36" tire made by the Coker company. Many different frames and configurations have used that tire. Several manufacturers such as The Unicycle Factory and RBR offer even larger wheeled unicycles. Sem Abraham has ridden the largest wheel at 73"...he required blocks to reach the pedals!