Bearings are the rings that fit inside your wheels which allow the wheels to spin. Bearings come in sets of eight and are inserted on each side of the wheel.
ANATOMY OF BEARINGS
Bearings allow for the smooth turning of a wheel on its axle. Bearings consist of 6, 7, or 8 balls enclosed in races between two shields encased in a disc-like body. To the right is a diagram of Bones Swiss bearings.
BEARING SHIELDS
The bearing shield plays an important role in keeping dirt from getting into the bearing and slowing it down. Some bearings have only one shield and can be taken apart for maintenance.
INNER & OUTER RACES
The races are the tracks the balls roll in. The balls fit between the inner and outer raceways within the retainer.
BALLS
These are in sets of 6, 7, or 8 balls which roll on the raceways. They are primarily made from steel. You will also find bearings made from lighter, more durable titanium alloys and ceramics which are considered the best materials you can buy.
RETAINERS (CROWNS/CAGES)
Retainers are also called crowns or cages and are usually made of Delrin. They hold and separate the individual balls in a bearing.
Delrin is a lightweight, low friction and wear resistant thermo plastic made by Dupont which can stand temperatures up to 194 degrees Fahrenheit.
C-CLIP
The C clip is a mechanism for locking bearing shields in place. It is essentially a thin C-shaped wire that fits tightly into a groove around the outside perimeter of the bearing shield to hold it in place against the bearing casing. Not all bearings have a C clip, but those that do can usually be taken apart for cleaning and maintenance.
CASING
The casing is the body of the bearing. It holds the ball bearings, retainer, and shield in place.
Portions of these definitions were from the following excerpt http://en.wikipedia.org/wiki/List_of_skateboarding_terms#Bearings
MATERIALS
STEEL is the most common material used to make bearings but great advances have been made to create bearings out of other materials such as titanium and ceramics. You’ll pay a little more for these materials because they last much longer than traditional steel ball bearings.
TITANIUM is much stronger than steel and doesn’t rust. It is also very lightweight which allows for a faster spin. Titanium bearings are not 100% titanium. Only some parts are made out of the titanium alloy. This is a great medium priced alternative to traditional steel bearings.
CERAMIC bearings are the best of the best. Bones Swiss Ceramics are an ideal example of well made ceramic bearings that are lighter, harder, stronger and longer lasting than the best steel ball bearings out there. Ceramics will last much longer than any ABEC rated bearing and will never rust. The ceramic balls will help to re-polish the steel races flat again, providing a self-healing benefit because ceramic balls are so much harder than steel. The lightweight ceramics allows you to roll faster and further. These will last the longest of any material, and will come with the highest price tag. Many say that for how long they last and how much less you need to clean them, it’s worth every penny.
ABEC RATING SYSTEM
Currently, most skateboard bearings are rated using the ABEC system.
What the heck is ABEC you ask?
ABEC stands for Annular Bearing Engineers' Committee, and is the American method for rating the accuracy and tolerance of bearings. ABEC standards are set by the American Bearing Manufacturers Association (ABMA) and range from 1-9 using only odd numbers (ABEC 1,3,5,7,9). An ABEC rating is merely a tolerance rating which measures the accuracy of the dimensions used to design the bearing. The higher the ABEC rating the faster the bearing can spin.
CRITICISMS OF THE ABEC RATING SYSTEM
The downfall of the ABEC rating system is that these guidelines were created to rate machine bearings, not skateboard bearings. For example, the ABEC system does not take into account durability which is key to the beatings a skateboard can take over time. ABEC ratings do not rate how a bearing can handle a side loads that occur in skating. It also does not measure speed, but the rate of efficiency the bearings move.
Some companies have chosen not to show the ABEC rating. Due to the rating systems limitations, it’s not necessarily a bad thing that they don’t show the rating. Many skaters commend these companies for this reason. Bearings such as Bones Reds were designed specifically for skateboarding and they do not see the need to use an ABEC rating.
WHICH ABEC RATING SHOULD I USE?
You’ll find more of the less expensive complete decks come with ABEC 3 bearings while most skaters, on average, use ABEC 5 bearings.
ABEC 5’s deliver good performance for the money. They perform better than ABEC 3’s and are cheaper and stronger than ABEC 7’s. The higher the ABEC rating the weaker the bearings become. That’s why ABEC 5 bearings are a safe choice. Some say you can’t even skate as fast as a true ABEC 7 will allow.
ABEC 7 bearings are very smooth and fast but are more expensive. ABEC 9 bearings are extremely fast, so only get them if you are looking to bomb hills or get some serious speed. Be prepared to pay a premium for a true set of ABEC 9 bearings.
Please note that the ABEC rating system does not account for many other things such as the quality and reputation of the manufacturer. A good bearing produced by a reputable manufacturer outweighs the significance of the ABEC system and justifies that quality comes at a cost. Good bearings will have super-finished raceways (contact surfaces), quality ball precision, use premium oil and have a well built retainer and seal using quality materials. Do some research to figure out what will fit your budget and suit your style of riding.
HOW ARE THEY RATED?
Not that you need to understand this, but these are the four questions asked to determine the ABEC rating of a bearing:
1) How close is the bore to 8mm in microns (a micron is 1/1,000 of a milimeter)
2) How close is the outer diameter to 22 in microns?
3) How close is the width to 7mm in microns?
4) What's the rotating accuracy in microns?
OTHER RATING SYSTEMS
ABEC is not the only standard in rating skateboard bearings; however, you won’t see the International Standards Organization (ISO) system or the German National Standards Organization (DIN) on skateboard bearings anytime soon. Below is a chart to give you an idea of how each would compare. You’ll notice how the ABEC system is the exact opposite of the two other rating systems.
ABEC Int'l Standards Org. German Nat'l Standards Org.
ABEC 1 ISO 0 (or "Normal") DIN P0
ABEC 3 ISO Class 6 DIN P6
ABEC 5 ISO Class 5 DIN P5
ABEC 7 ISO Class 4 DIN P4
ABEC 9 ISO Class 2 DIN P2