Buying Guide - Bearing ABEC Ratings
The ABEC rating system has been around for the last 35 years. The purpose of the ABEC committee (Annular Bearing Engineers Committee) is not to test every manufacturer’s bearings and proclaim them good or bad, but to establish dimensions, tolerances, geometry, and noise standards for bearings in an attempt to aid industrial bearing manufacturers and users in the production, comparison and selection of bearings for general applications. However, since every bearing is used in a different manner and environment, bearings should be redesigned or "customized" for special uses (like skating).
The ABEC rating system is not intended to be the only criteria used for selecting bearings for use in specialized applications like skating. It is only one of the tools a bearing designer can use if it is appropriate for the application.
The ABEC rating system includes grades 1,3,5,7, and 9. The higher the ABEC rating, the tighter the tolerances are, making the bearing a more precision part. High precision and small tolerances are required for bearings to function at very high RPM, in products like high speed routers that must spin at 20 to 30,000 RPM. In an application like this, an ABEC - 7 or 9 bearing rating may be appropriate. However, a skateboard with 54mm wheels turning 20,000 RPM will be traveling about 127 MPH! Since virtually all skating is done under 30 MPH, the realistic maximum RPM your skate bearings will see is about 4700 RPM and probably 90% of skating occurs under 2000 RPM. Thus, very high precision is not required at skating speeds.
The dimensions and tolerances controlled by the ABEC standards include the diameters and widths of the raceways, their shapes to some extent and the smoothness of the running surfaces. The ABEC rating system ignores side loading, impact resistance, materials selection and grade, appropriateness of lubrication, ball retainer type, grade of ball, the clearance between the balls and the races, installation requirements, and the need for maintenance and cleaning. All these bearing design requirements are very important to the performance of your skate bearing, even though the ABEC rating says nothing about them.
Information sourced from Bones - http://bonesbearings.com/support/abec/