Bearings and their various advantages and disadvantages are tremendously controversial in the inline-skating community. Most inline skates use some version of an industrial bearing termed '608'. I have heard that this was a historical accident that the 608's were the closest fit to the original quad rollerskates. 608's are made of metal, usually steel and contain seven ball-bearings that roll around a perimeter "race". Skates use two bearings per wheel, so typical rec skates use 16 bearings and 5-wheeled racing skates use 20. There is a standards certifying organization called ABEC which rates bearings according to the precision of the bearing measurements and tolerances. ABEC 1 have the least precise measurements, ABEC 3 have greater precision and tighter tolerances and come standard in most mid-to-upper range rec skates. ABEC 5 bearings are still more precise and can be found in some upper-range rec skates. ABEC 7's are about as high as skating bearing ratings go, and have to ordered separately and installed on your own. The controversy arises in part because industrial bearings are designed to spin without lateral loading, which is where most of the stress comes from in skating. Also, the higher-spec'd bearings are designed for very fast spinning, heavy, non-lateral industrial loads, not the relatively very low speed spinning, minimal weight lateral loads that a skater applies. Accordingly, it is largely a matter of opinion whether using a more precise bearing confers any greater speed. There are also Swiss (not necessarily made in Switzerland, but made from sturdier materials) bearings which are ABEC unrated but which perform very well under skating conditions. Many people race on Swiss bearings. Then there are variant bearing such as 608 variants with 8 ball-bearings instead of 7, bearings with ceramic rather than metal balls, and radically different "mini-bearings" with many more but much smaller bearings and hollow inner cores replaced by an extended nylon spacer. These bearings provide huge weight savings, taking advantage of the fact that 608's are extremely over-spec'd for skating and chopping out a lot of the 608 metal. If this sounds confusing, it's because it is. Personally, I loved the Swiss, because they were quick and easy to maintain, but I have no facts on whether one type lets you skate faster than any other, just lots of opinions. :)