The ABEC rating controls the Balls in the bearing and the higher the rating the less free space in the bearing. Rebel you are correct in saying the higher rating will have less run out but the seal is the same.
The seals are attached to the outer ring and the lip of the seal contacts the inner ring. This seal is not sprung or anything positive, its only a rolled rubber lip. Any dirt, dust or water doesn't have to try very hard to get past it and then as Mark said less dirt does more damage in the higher tolerance bearing for the reasons we've already discussed.
Hope that helps
|