Bearings - terms explained

Bearings for the roller skates is necessary for the wheels to rotate. Different terms are used when talking about bearings. This guide provide you with an explanation of the different terms that exists.

Notice: Avoid water & sand.
A bearings lifespan will be shortenend drastically when riding /stored in moist surroundings.
 

Composition

The bearing contains: - an outer ring - an inner ring - a number of balls (6-11 in a bearing), - a bearing-cage - up to 2 shiels/seals. The balls are kept in position by the cage and a raceway in the outer and inner ring.

Size
Today 2 sizes is the standard that is used in bearings:

Normal bearing The most common for all types of roller skates and skateboards. In industrial-language this is a 608 bearing (600 series, 8.0 mm diameter). The outer diameter is 22.0mm and the width of the bearing is 7.0mm. Mini-bearing, also known as micro and baby bearings. Used for some speed and fitness skates. They are smaller and lighter than normal skate bearings. In industrial-language this is a 688 bearing (600 series, 8.0mm inner diameter). The outer diameter is 16.0mm and the width of the bearings is 5.2mm.

698: A bearing sized between normal and mini-bearings. Twincam have been selling these bearings for roller skates, but with only minor succes.

Material

Most bearings are made of steel. The quality of the steel is very determining for the durability of the bearing (because of pressure, shocks and dirt). The very cheapest bearings are made of pressed sheet metal or hardened carbonsteel, both types is not recommandable. Better bearings are made of real bearing-steel with chrome, some with titanium, rustproof steel or Swiss steel.

In ceramic bearings (usually used for speed skating) the balls are made of industrial ceramic (Silicon Nitride). Industrial ceramic do not rust and is more durable than bearing-steel. In some cheap ceramic bearings the balls are steel balls with a ceramic layer, and some of the best (and most expensive) ceramic bearings are full ceramic (both balls, inner and outer ring is made of ceramic)

Precision

Bearings are divided according to the ABEC-specification. ABEC means Annular Bearing Engineers Committee, and is a specification for the measuring tolerances the bearing must keep. Please note that the ABEC-value does NOT say anything about how fast or how durable the bearing is.
Below is table with the different ABEC-values used in bearings for rollerskates:

A high ABEC-value represents a higher precision for the bearing. The way the precision affects the speed is minimal (unless you drive with speeds comparable to the speeds industrial bearings go with - which is minium 60 km/h on skates).
The precision for the spacers (0,01-0,1mm) and the plastic-hub of the wheel is remarkable smaller than for the bearing it self, and will probably be a more important factor at high speed skating. Also remember that a high-precision bearing does loose its precision and becomes a precision like an ABEC-3 or ABEC-1 bearing after some wear.
Conclusion: In the best case, the ABEC-value can be used as a rule of thum for how good the bearings are, and nothing else.

Shields/Seals

In order to prevent dirt, sand and water to enter the bearings, a shield or seal is often placed on each side of the bearings.

	A shield is usually a metal shield mounted to the outer ring, and has a littel space to the inner ring (also called a dustproof bearing). Bearings with shields have little friction and therefor more easily rotate, giving you more speed. On the other side is the bearing not perfectly protected against water and dirt. [foto from http://www.edswheels.com/]
	A seal on the is made of steelarmet rubber, which is mounted to the outer ring, and slightly touches the inner ring. It gives better protection and almost no maintenance, but also higher friction and lower speed. [foto from http://www.edswheels.com/]

The different kind of protection shield/shiels is listed in the table below together with an explanation (the type of the bearing is usually printed on the bearing together with the size, eg.: 608ZZ):

Lubrication

Bearings for roller skates is lubrication with either oil or grease.
Oil: Gives the higest speed because of less resistance in the lubrication material. Also more demanding, because maintenance is required. A thin oil gives higher speed, but also requires more frequent maintenance.
Grease: Gives the highest resistance agains water and dirt. Requires almost no maintenance, but on the other side will the higher resistance in the lubrication material result in lower speed.



Also check out these homepages about bearings:
skatefaq.com
edwheels.com