News Article

Thun Develops BB Cartridge for Belt Drives


ENNEPETAL, Germany – To meet growing demand for belt drive systems, bottom bracket cartridge specialist Thun developed the Mammoth. The company is specialist in the development and production of inner bearings for city, trekking, children’s and MTB.

Thun Develops BB Cartridge for Belt Drives
Thun’s Mammoth features four instead of the standard two ball bearings to stand the tension of the belt when the bike is parked. – Photo Thun

Contrary to chain drives, belt drives are always under stress to prevent it from jumping under load. Moreover, the ‘belt line’ has to be aligned precisely, because a skewed belt will adversely affect the operation, durability and smoothness of running.

Permanent stress on the ball bearings

According to Thun, the belt needs an initial tension of approximately 400N (40 kg) to meet these requirements. The tension on the BB-cartridge causes permanent stress on the ball bearings. When the rider starts to pedal, this weight even comes on top of the 400N.

However, for most of the time bicycles are is parked in a garage. Nevertheless the ball bearings have to stand the constant punctual load of 400N although they are not designed for this, resulting in additional wear.

To avoid this wear Thun created the Mammoth, featuring four instead of the standard two ball bearings. Thun claims that while the initial tension on the belt remains the same, the wear will be halved as long as the bike is parked.

Next to the Mammoth, Thun also developed the optional ‘stopper ring’. Mounted on the right hand side it results in a precise positioning of the crank on the axle after assembly. According to Thun this feature ensures the alignment of the belt.

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