Bottom Bracket Basics



Getting Started! 

Bottom Bracket standards getting you down?  Do you look at your cranks and think "Why bother?" Are you ready to give it all up and start roller blading?  We're here to help.

 

This guide will help you identify the type of bottom bracket you'll need and which cranks will be compatible.  Before we get into specifics, we should define a few terms.

 

Bottom Bracket Shell – The part of the frame that accepts the bottom bracket and crank.  The type of bottom bracket necessary for that frame can be identified by the Internal Diameter and Shell Width.

  • Bottom Bracket Shell Internal Diameter –The Internal Diameter of the Bottom Bracket Shell will be the same as the Outside Diameter of the Bottom Bracket Cup. 
  • Bottom Bracket Shell Width – The Shell Width will determine the length of axle, and spacers necessary to run a given crank on the frame. 

 

Bottom Bracket – The component pressed or threaded into the frame, that the crank will fit into

  • Bearing – The sealed cartridge containing ball bearings, grease and seals, that the crank rotates on.  Usually listed as having Steel or Ceramic ball bearings.
  • Bottom Bracket Cup – The aluminum/plastic/steel housing for the bottom bracket bearing
  • Bottom Bracket Outside Diameter – The Outside Diameter of the cup will be the same as the Inside Diameter of the Bottom Bracket Shell
  • Bottom Bracket Inside Diameter – The Inside Diameter of the Bearing will be the same as the Spindle Diameter

 

Press Fit Bottom Bracket– Any bottom bracket that is installed in the frame with a press

 

Threaded Bottom Bracket – Any bottom bracket that is threaded into the frame

 

Spindle – The part of the crank that slides into the bottom bracket and rotates on the bearings.  They come in four diameters:

  • 30mm - Found on most modern cranks
  • 24mm - Found on all Shimano cranks, and some FSA options
  • GXP -  Found as an option on SRAM cranks, and from some other manufacturers.  GXP is a 24mm spindle, that steps down to 22mm on the non-drive side.
  • DUB – SRAM specific spindle, measuring 28.99mm.  This is a new standard, and only used on some SRAM products

 

Handy Facts!


  •  BB30 is the most commonly misused term when talking about bottom brackets.  Most people will refer to their cranks and frame as BB30, any time it uses a 30mm spindle or bottom bracket is present.  Since BB30 was the first 30mm option, it has become a shorthand for this entire diameter, which makes it challenging to figure out the bottom bracket that your bike will need.  Always check your frame manufacturers website before ordering a bottom bracket!
  •  Most frames will accept any spindle diameter.  Just because your bike has a 24mm bottom bracket currently, doesn’t mean that you can’t switch to a 30mm crank when you decide to upgrade.  The only exception is the BB90 found on Trek Road Bikes and BB95 found on Trek Mountain Bikes, which are 24mm specific standards.

 

Threaded Bottom Brackets

 

BSA

Found on many steel bikes, and many Mountain Bikes

  • The Bottom Bracket Shell will measure 68mm wide on a road bike, and 73mm wide on a mountain bike. Both will have a threads on the inside of the shell.
  • One of the oldest designs, considered to be very reliable.
  • Can use both 30mm and 24mm cranks with the appropriate bottom bracket.

 

ITA

Found on Italian Road Bikes

  • The bottom Bracket Shell will measure 70mm and have a threads on the inside of the shell.
  • Can use both 30mm and 24mm cranks with the appropriate bottom bracket.

 

Press Fit Bottom Brackets

 

BB30

Found Primarily on Cannondale, and some Specialized Road Bikes

  • The bottom Bracket Shell will measure 68mm wide on a road bike, and 73mm wide on a mountain bike. Both will have a 42mm Inside Diameter. 
  • Bearings press directly into the frame, without a cup, and stop at removable snap rings; two snap ring grooves will be present inside the shell. These snap rings are the easiest way to identify a BB30 frame
  • Can use both 30mm and 24mm cranks with the appropriate bottom bracket.

 

PressFit 30 (PF30)

Used on a huge array of both road and mountain bikes

 

 
  • The bottom Bracket Shell will measure 68mm wide on a road bike, and 73mm wide on a mountain bike. Both will have a 46mm Inside Diameter. 
  • While PF30 is commonly mistaken for BB30, they differentiate in two easily identifiable ways:
    • The PF30 uses a bearing with a cup, as opposed to BB30’s direct press into the frame
    • PF30 does not use snap rings, and has no grooves in the Bottom Bracket Shell for them.
  • Can use both 30mm and 24mm cranks with the appropriate bottom bracket.

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    BB86/92

    Commonly found on Giant, Fuji, Pivot and many other bikes

     
  • The bottom Bracket Shell will measure 86mm wide on a road bike, and 92mm wide on a mountain bike. Both will have a 41mm Inside Diameter.
  • Can use both 30mm and 24mm cranks with the appropriate bottom bracket.

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    BB90/95

    Found exclusively on Trek Road and Mountain bikes

     
  • The bottom Bracket Shell will measure 90mm wide on a road bike, and 95mm wide on a mountain bike. Both will have a 37mm Inside Diameter. 
  • Bearings press directly into the frame without a cup. Unlike BB30, the frame has a lip designed to stop the bearings.  No snap rings are used. 
  • Can use ONLY 24mm cranks!
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    BBRight Pressfit

    Found on all Cervelo Bicycles

     
  • The bottom Bracket Shell will measure 79mm wide with a Inside Diameter of 46mm.
  • BBright is an asymmetric version of PF30. It is offset 11mm to the non-drive side. 
  • Can use both 30mm and 24mm cranks with the appropriate bottom bracket.
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    BB 386 Evo

    Found on some Road Bikes

     
  • The bottom Bracket Shell will measure 86mm wide with a Inside Diameter of 46mm.
  • BB 386 EVO is a wider version of PF30.   
  • Can use both 30mm and 24mm cranks with the appropriate bottom bracket.
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