bearing
TECHNO­LOGY

DT Swiss hubs are designed to function optimally once installed in a bicycle. To achieve this, the clamping force created by the wheel mounting system must be taken into account when constructing a hub. Learn how to ensure the optimal rotating property of the ball bearings and discover why DT Swiss does not offer hubs with adjustable bearing clearance.

bearing clearance

In order for a bearing to rotate, there must be a certain amount of play in the thousandth of a millimeter range. Without this clearance, the bearing cannot rotate. Bearing play occurs both radially and axially. Axial clearance describes how far one bearing ring can be displaced longitudinally relative to the other without load. Radial clearance is measured vertically to the center axis of the bearing.

Radial play (left), axial play (right)

hub construction

DT Swiss hubs are engineered to have the optimum axial and radial bearing clearance when the hubs are properly installed in the wheel and bike. To achieve this, it is important to assemble the hub in the correct order.

To start, the first bearing is pressed into the hub shell so that it sits flush with both the shell and the axle.

Bearing sits flush with hub shell and axle
Hub cross-section with press-fit tool (left) and guide tool (right)

The second bearing is then pressed in so it sits flush with the axle, but not with the hub shell. Therefore the axle is minimally compressed. The bearing sits at a press-fit, in which the outer bearing ring can no longer move relative to the hub shell.

Bearing sits flush with axle
Hub cross-section with press-fit tool (right) and guide tool (left)

 

preloaded ball bearing

The axle is now slightly compressed axially and exerts a force on the inner rings of the bearings. This causes the bearings to be preloaded. 

Bearing preload due to axial force

The inner or outer bearing rings thus press on the balls. This results in frition when the bearnings are not installed, which is also noticeable.

Bearing with preload in the non-installed state

minimum friction

If the hub is now installed in the frame or fork, a clamping force is transmitted to the axle by the wheel mounting system, which compresses the axle and thus acts against the initial preload of the bearings. As a result, the bearing rings no longer press axially on the balls and the bearings can thus rotate optimally with minimum friction when installed.

Clamping force of wheel mounting system

If, on the other hand, the axle and bearings were not preloaded before installation, the clamping force of the wheel mounting system would compress the axle and thus lead to increased friction of the ball bearings when installed.

Bearings in installed condition

 

One question remains. Why doesn't DT Swiss use hubs with adjustable bearing play?


The art of designing a durable hub with minimal play lies in the proper preload of the bearings. In most bicycle hubs radial bearings are installed, which are susceptible to lateral forces. Hubs, with systems to adjust the play, usually have a fine thread. These allow fine adjustment of the clearance, but they are also capable of generating large axial forces. Thus, the bearings are very quickly over-preloaded, which damages the bearings.

Years of experience regarding optimal bearing preload and knowledge of production tolerances, allow DT Swiss to design durable, play-free hubs without bearing play adjustment. With this hub design additional weight can be saved again, since no threads need to be considered in the design, which allows a thinner wall thickness. Another advantage is easy maintenance and quick conversion to the various freewheel and axle systems.

 

This bearing technology appears in every DT Swiss hub, front and rear.