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Shimano UN55 Bottom Bracket

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Product Details

Shimano UN55 Sealed Bottom Bracket

Consistently great quality cartridge sealed Shimano bottom bracket. The UN55 has a metal LH cup. Metal cups tend to be much easier to remove in years to come compared with the nylon cups some bottom brackets such as the Shimano UN26 employs.

The Shimano UN55 works well with any near-any modern crank that fits a traditional 'square taper' (as opposed to splined) bottom bracket so the UN55 comes in loads of sizes:

  • The first number (eg 68) refers to the width of the frame's bottom bracket shell. This is usually 68mm but some companies prefer 73mm.
  • The second number (eg 113) refers to the length of the axle (ignore the threaded portion). Generally speaking, modern low profile cranks use short 110 and 113mm axles. Older bikes with straighter cranks like Shimano Tourney usually need a longer 122.5mm axle. If your present setup works fine chainline-wise, don't mess with a good thing. Replace it with an axle of the same length.
  • Where 2 axle lengths will work equally well, we would always recommend the shorter one (it's stiffer and it has a lower Q-factor) - as long as the crank still clears the chainstays.
  • UN55s are all British Standard threading because this is the international standard used on almost any bike made in Britain, the USA, China, Taiwan and Japan.
  • 346g based upon weighing one example of this bottom bracket at Edinburgh Bicycle Co-op's head office in October 2011.