Skateboard Wheels are important! You've heard how the story begins: Man Invented Wheel. Just as important, and more relevant is the breakthough in skateboard wheel technology and options offered over the last 30 years. Your skateboard wheels are the part of your skateboard that allow you to move, and help to ultimately determine how fast you can go and what conditions you can ride in. Skateboard Wheels are made by many skate brands and come in a wide selection of sizes to suit many styles, and graphics to suite many tastes. These days they are almost always made of polyurethane. There are two factors to consider when buying the skate wheels that are right for you: the Size, and the Hardness. The size of skateboard wheels is measured by the diameter and usually expressed in mm. Size is most variable option but you quickly find what suites you best. Many skaters know which wheel size they prefer and it's all a matter of comfort and feel. Here's a basic Guideline for you: Small Wheels (50-53mm) are slower but made for stability and being light-weight. These are for park riding and trick focused skaters. Medium sized wheels (54-59mm) are designed for a bit more speed on smoother surfaces, usually for parks, bowls, and vert ramps. Larger wheels (60mm+) are speciality wheels for longboards, old school cruisers, downhill racers. These are made for speed and stability on rougher surfaces.
The Hardness of a wheel will certainly play a role in the feel of your setup. "Hardness" is measured by the Durometer of the polyurethane after processing. There's a lot of science behind creating these options for modern skateboard wheels (which are generally referred to as wither 'soft', 'hard', and 'extra hard') but generally speaking if you are doing technical tricks on a shortboard, smaller and harder wheels are the natural choice. For cruisers and longboards, larger wheels give you the speed and balance you will need. Your weight can affect what size wheels feels right for you, but when in doubt stick to firm 99a or 101a wheels.