A few years ago a lot of roller skates came with 627 Z bearings but these days most manufactures choose 608 Z bearings for roller skates. For skateboards and inline skates only 608 Z bearings are used since several years - this way all manufacturers could concentrate on one construction type. This developement is also recognizable in roller skate market. It makes upgrading and customizing much easier for customers.
Bearings in 608 Z form have a outer diameter of 22mm, a width of 7mm and an inner diameter of 8mm. (A 627 Z bearing has the same measurements except the inner diameter which is only 7mm.)
The construction of these bearings is always the same: The bearings cosists of an inner ring, an outer ring and a cage in which the balls are placed. The cage ensures the distance between the balls. The balls run between the inner and outer ring. Cage and balls are lubricated with oil of grease ensure long lifetime, higher speeds and smoothness.
The cage which holds the balls is often made of plastic or metal. The balls are made of steel or high-end ceramic. Ceramic balls are much more stronger than steel balls and their surface structure is more sleekily. Because of the manufacturing process the ceramic balls are heat-proof and extremly durable.
The bearing is protected against dirt and dust by a cover disc (shield). Mostly, these cover discs are removable to allow cleaning and servicing of the bearing. Cleaning work is extremly high and is normally not made from a skater. You use the bearings until they do not roll in a free way anymore. Then they have to be replaced by new ones.
It is also possible to get bearings with shields that should protect against water and therefore against corrosion. But of course a bearing will never be completely closed because the shield always need a little bit space between the inner and outer ring to move. But since a few years some manufacturer developed something innovating: A so-called Labyrinth-Shield. Inner ring, outer ring and shield are build like a labirinth. That means the dust cannot find a direct way into the bearing. Dirt has to "go around several corners" to come into the bearing. With these bearings a stress-free skating is guaranteed - in addition these bearings are clearly faster and require less maintenance. The GRINDHOUSE ABEC-9 bearings feature such a shield: GRINDHOUSE bearings.
The quality unit of InlineSkate bearings is stated in „ABEC“. ABEC means Annular Bearing Engineering Committee, a Technical Committee of American Bearing Manufacturers Association (ABMA), an association of American bearing producers. The measure effects in different steps: ABEC 1, 3, 5, 7 and 9.
----> The higher a ABEC-step, the more quality a bearing has!
Lubricants are seperated into greases and oils. To make a bearing very fast you should use bearing oil to lubricate it. Bearing oil has the advantage that it ensures a lower frictional resistance than grease and is better for starts and is recommended for a faster rolling experience. Unfortunately it elapses and therefore attracts dirt and dust. Bearing grease has the advantage that it'll stay much longer inside the bearing. So you have a longer protection but it is hardly fast.
The best solution is very fine lubricant, as it combines the qualities of oil and lubricant. To have a very good and fast rolling experience not only the bearing has to be good. A lot depends on spacer, frame and certainly wheels. A first-class wheel in combination with a first-class bearing, driven precisely through spacer and framewasher in the frame, allow the most frictionless sprint.
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