Skateboard wheels are essential in determining board feel. There are many different wheel options. They all vary in size, durometer (hardness) and cut. Skate wheels are most commonly made of polyurethane.
Wheels are all personal preference. However, when selecting your wheel size keep in mind that most street skaters will select a wheel from 50 to 54 mm, dependant of the height of your trucks. Wheels which are larger are more suitable for park or vert and bowl skating.
With regards to wheel hardness, the rule of thumb is harder equals faster. Whilst softer wheels give better grip and a smoother ride, this makes them more suited to cruising. Harder wheels are ideal for street skating.