Hubs, central and yet mostly asymmetrical
The hub sits in the centre of the wheel, holds the spoke heads, and does the actual turning work. In conventional hubs, the spokes sit in the hub flanges, which are the two plate-shaped highest points. In straight pull systems, the flange does not form a plate and has a significantly smaller diameter. The two flanges of a hub can have the same or different diameters. The space between the flanges determines (besides the rim diameter ERD, see below) the spoke angle. The flatter the spoke angle, the more stable the wheel, which is why hubs have become wider in recent years. Front wheel hubs for rim brakes are symmetrical; with disc brake hubs the brake disc needs space on the left side, which is why the left flange is indented. Rear hubs are much more often asymmetrical because they have to make room for the cassette on the drive side. Symmetrical rear hubs are found on singlespeed or track bikes. As a result of all this, you will most likely need spokes of various lengths on the left and right side of the rear wheel, so that the rim rests centrally in the frame at the end. However, the difference can be reduced or compensated by asymmetrical rims or unequal hub flanges. On the front wheel, the deviation may be so slight that the same spokes will fit on both sides. When you measure the hubs yourself, you determine these values: over locknut dimension, flange distance, flange centre to the outer edge left and right (or to the centre, depending on the calculator), flange diameter and spoke hole diameter.