The easier they roll the more you will enjoy skating. However, a wheel that rolls too fast may put you beyond your comfort zone. Wheels may be too hard or soft for the intended surface, causing a bumpy or mushy ride. They may be too big, reducing maneuverability. The size is important because the larger the wheel, the faster it rolls.
Smaller wheels are more maneuverable and stable, but roll more slowly.
Most recreational skates come with 72-76mm diameter wheels. Sizes can range from 44-80mm. Thinner wheels are faster but less stable than thicker ones. The wheel's size will be marked on its side. Hardness - Wheels are made out of urethane, a plastic material whose hardness can be varied.