Heely's are shoes that have a removable wheel in the back of the shoe's sole. These shoes allow the wearer to roll across flat surfaces by lifting their toes and putting one foot in front of the other. Heely's also serve as a normal shoe when the wheels are removed. Heely's are all very similar and can be worn with one or two wheels.
Balance
Heelys with two wheels are generally easier to learn on. They are better for smaller children who don't have a good sense of balance yet. The wheels are positioned one in front of the other with the first one in the center of the shoe. Heelys with one wheel are for those who have experienced wearing the two-wheeled Heelys. Those who have experience rollerblading or ice skating are also candidates for one-wheeled Heelys. The wheel is positioned in the back of the shoe under the heel.
Turning and Speed
Two-wheeled Heelys are more difficult to turn on and are slower because it takes more energy to move two wheels. The one-wheeled Heelys are easier to maneuver on and can go faster. More complex moves can be done on one-wheeled Heelys than the two-wheeled version. If you have experience ice skating or rollerblading then attempting turns on Heelys shouldn't be much of a problem.
Interchangable
Heelys with two wheels do not come with the removal tool or sole savers which are inserted in the hole once the wheel is removed. They can be purchased separately. While it is easy to remove the wheels, it's twice as much work to remove two wheels than remove only one. Purchasing the additional sole saver can also increase the cost.
Styles
Two-wheeled Heelys are not available in all sizes and styles. The one-wheeled Heelys are the more popular form, and are available in every size and style you can find online or in stores.