The Hub shell
The hub shell is provided with flanges with spoke holes and cups for the ball bearing. The hub sleeve may also contain components with which a force can be exerted on the wheel. At the rear this is the sprocket or freewheel (Fig. 44) . In addition, it is very often that a hub house pedal brake, drum brake, disc brake or roller brake. Even the dynamo can be arranged in the hub. The number of spoke holes determines which rim fits the hub. The diameter of the spoke holes is decisive for the wire diameter to be applied. The spokes have to have a little space in the spoke hole. Good spoke holes are gesoevereind. Because of this, the wire well in the spoke holes at the turn. If dynamic flat spokes to be used must be provided with the spoke holes in the flange of special notches. The flat spokes may then be threaded through this notch.
Cheap hubs are made of chromed steel. In these hubs cups for bearing directly into the steel squeezed it. More expensive hubs are turned from aluminum which is forged in the raw form. In the hubs be pressed steel cups for the ball bearing. The aluminum is too soft for use as a running surface for the ball bearings. At a fixed hub shell for ball bearings is rotated in a press-fit to the hub shell. Aluminum can to beautify polished or anodized appearance. The diameter of the hub shell determines how well the forces on the left-hand and right-hand hub flange are distributed. The larger the diameter, the greater the torsional – stiffness of the hub shell, and thus the force distribution. This is especially important when there are heavy forces are exerted on the wheel by drive and braking. Shimano hubs used for the indication parallax with large diameter.
Hubs, there are high and low flange. Wheels with high hub flanges have shorter spokes. Through the use of short spokes the wheel is stiffer.
The spoke is at a high load with low hub flanges by drive and braking forces, by a high flange hub, the spokes further arranged from the center of the shaft. A hub with high flanges is therefore better suited to transmit drive and braking forces through the spokes to the rim.
However, the high flanges are worse withstand side load and heavier than hubs with low flanges. Hubs with high flanges are therefore virtually no longer applied.