Fixing Tight and Undersized Bottom Brackets


A common theme in recent times is for manufacturers to reduce the size of their bottom bracket openings. This prevents the bearings from falling out from looseness but it has a severe impact on bearing life and rolling friction.

A classic symptom of a tight fit is bearings, which feel very smooth outside the bike frame and feel notchy or gritty once installed. Most of the time the bearings will bed in but it is highly dependent on the level of compression. Another common symptom is creaking. Excessive compression can crack the bearing cage and which manifests itself as a creak when loaded.

Installing a Hambini Bottom Bracket into an undersized frame can break the frame.

Undersizing affects all brands but is particularly prevalent in Cervelo, Canyon, Factor and Scott bike frames


An undersized bottom bracket is the result of a manufacturing fault of the bicycle manufacturer, the user should attempt to remedy this with them before attempting the procedure below. Hambini accepts no liability for any damages or personal injury arising from following this procedure.


Irrespective of the frame material, the procedure is the same – the material must be removed. In most circumstances, a flap wheel or cylinder honing tool will be sufficient as only a small amount of material needs to be removed.

  • For Frames using BB86, BB92 and BB30 Bottom Brackets, A cylinder honing tool is recommended
  • For Frames using PF30 and derivatives (BBright, BB386), A 50mm flap wheel is recommended.
  • A power drill will be required


This video shows you how to remove sufficient material to enable a good fit.

Once the process has been completed, then installation can commence