Wheels
The wheels of a Skateboard, usually made of polyurethane, come in many different sizes and shapes to suit different types of skating. Larger sizes like 65–90 mm roll faster, and also move more easily over cracks in pavement. Smaller sizes like 48–54 mm keep the board closer to the ground, require less force to accelerate and produce a lower center of gravity, but also make for a slower top speed. Wheels also are available in a variety of hardnesses usually measured on the durometer 'A' scale. Wheels range from the very soft (about 75a) to the very hard (about 101a). As the scale stops at 100a, any wheels labelled 101a or higher are harder, but do not use the appropriate durometer scale. Some wheel manufacturers now use the 'B' or 'D' scale, which has a larger and more accurate range of hardness.

Modern street skaters prefer smaller wheels (usually 45–53 mm), as small wheels can make tricks like kickflips and ollies easier. Street wheels are often quite hard as this allows the wheels to 'break away' from the ground easier. Vert skating requires larger wheels (usually 55–65 mm) as vert skating involves higher speeds. Vert wheels are also usually very hard, which helps with maintaining speed on ramps. Slalom skating requires even larger wheels (60–75 mm) to sustain the highest speeds possible. They also need to be soft and have better grip to make the tight and frequent turns in slalom racing. Even larger wheels are used in longboarding and downhill skateboarding. Sizes range from 65 mm right up to 100 mm. These extreme sizes of wheels almost always have cores of hard plastic that can be made thinner and lighter than a solid polyurethane wheel. They are often used by skateboard videographers as well, as the large soft wheels allow for smooth and easy movement over any terrain.

Bearings
Each Skateboard wheel is mounted on its axle via two ball bearings. With few exceptions, the bearings are the industrial standard "608" size, with a bore of 8 mm, an outer diameter of 22 mm, and a width of 7 mm. These are usually made of steel, though silicon nitride, a high-tech ceramic, is sometimes used. Many skateboard bearings are graded according to the ABEC scale. The scale starts with ABEC1 as the lowest, 3, 5, 7, 9. It is a common misconception that higher numbers are better for skateboarding, as the ABEC rating only measures tolerances, which do not necessarily apply to skateboards. The ABEC rating does not determine how fast or how durable a bearing used for skateboarding will be. In particular, the ABEC rating says nothing about how well a bearing handles axial (side-to-side) loads, which are severe in most skateboard applications. Many companies do not show the ABEC rating, such as Bones Bearings, who makes bearings specifically for Skateboarding. These bearings are usually called swiss or ceramic and are better for skating

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