Working on the eccenter / BB eccentric - Advanced skills only

Please note that due to important cables located inside the bottom bracket, working on the eccentric housing is only recommended with absolute care and some advanced bike maintenance skills. Contact us if you have any questions

To tighten (or loosen) the Gates belt, first loosen the two bolts with a 6mm hex key on a Generation 1 bike or with a 5 mm hex key on a Generation 2 bike at the frame opening in the bottom bracket area, see photo point 1. Once the two bolts are loosened, the eccentric housing in the middle of the bottom bracket can be moved, which tensions the belt. Now proceed as follows:

  1. On the left-hand side (the side with the power button) of the bottom bracket there is a recess (see photo, point 2) into which you can insert an 8 mm hex key on a Generation 1 bike or a 6 mm hex key on a Generation 2 bike to move the eccentric. The recess is only there to move the housing with the help of the hex key, there is no bolt in it.
  2. Turn the eccentric clockwise until the belt tension is sufficient. Check the tension with the Carbon Drive App. Be careful, however, if the belt tension is too high - this can lead to noise and wear.


The bottom bracket, which is built into the eccentric housing, has an important cable. To tension the eccentric bracket, it must only be moved clockwise as described above, otherwise the wiring can be damaged if it is twisted. If you thus want to loosen the belt again, be very careful.

Also make sure that the housing remains as a unit in its centre position, i.e. that it is not pushed to the right or left, otherwise the belt will not run smoothly and cables could be damaged. Now you can tighten the two bolts on the frame opening evenly with 10-12nm. At best, clean and grease them first.

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