A ball bearing is a bearing in which metal balls move in a ring around the wheels so that they turn more easily and reach higher speeds, with less rubbing. Each wheel has two of these plus one separator, which are respectively attached to each of the ends of the axles. In total, then, there are four wheels, eight ball bearings and four separators in each skateboard. There can be six, seven, or eight little balls in each metal –generally aluminum– ring. Among all the systems to measure ball bearing resistance, ABEC (Annular Bearing Engineering Committee) stands out as the most widely known. Its standard of measurement is the ABEC, an odd-numbers-only scale of 1-9, 1 being the least resistant and 9 the most resistant. However, there are other systems not so well known, such as DIN (Deutsches Institut für Normung) and ISO (International Standards Organization), whose scales are opposite to that of ABEC, i.e. the smaller a figure, the higher degree of resistance. Now, if you want to be an expert in this field, you should be familiar with this resistance thing; as for us, technical details are not our main concern here.
Besides, resistance doesn’t necessarily imply more speed "although it certainly implies spending more money". In other words, you mustn’t take it for granted that if you buy a ball bearing classified as, say, ABEC9, there will be no question about it being fast. Speed, in fact, depends on how carefully treated ball bearings are (e.g. it is essential that they are well lubricated), rather than on their resistance. Just for you to know, only if your skateboard could go at 530 km an hour would its ball bearing resistance influence its going.
Swiss ball bearings are said to be the best. However, many companies label their own ball bearings "Swiss" although this is untrue, claiming that the production methods are the same. Therefore, you should always check packaging before buying.
In order to keep a ball bearing in good condition, periodic cleaning and lubrication is very important. Oil and grease are good lubricants. On the other hand, to clean up the dirt, and the oil and grease accumulated because of lubrication, it is advisable to use some kind of solvent, e.g. turpentine or gasoline.
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