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Eccentric Bottom Brackets

An Eccentric Bottom Bracket (EBB) is a unique type of bottom bracket with concentrically-offset bearings that may be rotated slightly to change the position of an integrated crank spindle, effectively adjusting chain tension without moving the rear wheel or adding an additional chain tensioner.

Eccentric Bottom Brackets have several uses on a bicycle:

  • Chain Tensioning (Single Speed, Fixed-Gear, and Internal Gear Hub Bikes)
    • On frames with vertical dropouts where you can't slide the wheel back to tension the chain, an EBB allows for fine adjustment of chain tension
  • Belt Drive Systems
    • Belt drives require precise tension with no slack. An EBB provides a simple, clean, and reliable means to dial in belt tension on frames with vertical dropouts.
  • Bottom Bracket Height Adjustments (Suspension or Tandem Bikes)
    • Rotating the EBB slightly raises or lowers the crank’s integrated spindle. This can be helpful in changing the bottom bracket height to fine-tune pedal clearance for MTBs or tandems, or to slightly adjust a rider’s fit.
  • Tandem Bikes (Timing Chain Tensioning)
    • The timing chain on tandems connects the front and rear cranks and must be properly tensioned. An EBB installed into the captain’s front bottom bracket shell makes it easy to keep the timing chain tight.
  • Gearbox and Special Drivetrain Setups
    • Some frames with gearboxes or alternate drivetrains use EBBs to handle chain or belt tensioning when traditional methods aren't possible.
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Revolvr Eccentric PF30 Bottom Bracket

Part # 121316
  • Converts a PF30 (46 mm x 68/73 mm) frame to a single speed or fixed-gear setup
  • Compatible with both HTII and GXP integrated spindles
  • CNC machined AL6061 cups
  • Sealed bearings
  • Three bolt design for a secure fit
  • Includes spacers, a GXP shim, and a wave washer
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Revolvr Eccentric BSA Bottom Bracket

Part # 121317
  • Converts a BSA (1.37" x 24 tpi x 68/73 mm) frame to a single speed or fixed-gear setup
  • Compatible with both HTII and GXP integrated spindles
  • CNC machined AL6061 cups
  • Sealed bearings
  • Includes spacers, a GXP shim, and a wave washer
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Revolvr Eccentric T47 Bottom Bracket

Part # 121318
  • Converts a T47 (M47 x 1 mm x 68/73 mm) frame to a single speed or fixed-gear setup
  • Compatible with both HTII and GXP integrated spindles
  • CNC machined AL6061 cups
  • Sealed bearings
  • Includes spacers, a GXP shim, and a wave washer
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