The complete guide to bottom bracket standards

Want to know your BSA from your BB90?

This is the ultimate guide to bottom brackets

This comprehensive guide tells you everything you need to know about bottom brackets — from a breakdown of all the bottom bracket systems available and their compatibility with one another to how a bottom bracket works and how to stop a bottom bracket creaking, this guide has it all. 

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It wasn’t long ago that the only major bottom bracket decisions you had to make were shell width, spindle length, and, in rare cases, English (BSA) or Italian threading. These days, it can feel as though there are as many ‘standards’ as there are bike brands, with every one of them supposedly being the best option.

Below we rundown each of the major bottom bracket systems currently available, along with advantages, disadvantages, notes on compatibility, and some input from their proponents on why they exist:

  • Conventional/BSA threaded
  • BB90 and BB95
  • PF86 and PF92
  • BB30
  • OSBB (road)
  • BB30A and BB30-83 Ai
  • PF30
  • OSBB (mountain)
  • PF30A and PF30-83 Ai
  • BBRight
  • BB386 EVO
  • T47
  • Threadfit 82.5
  • SRAM DUB

Before we get stuck into the nitty-gritty of each standard, we’ve put together this helpful crib sheet that runs through all of the key specifications.

This is a fairly monstrous table, so you may have to scroll sideways to get the full picture.

Bottom bracket standards and compatibility chart

Name/
standard
Proprietary? BB shell inner diameter Bearing inner
diameter
BB shell width Installation Compatibility Other names Other notes
ISO threaded internal No 1.37in x 24 TPI N/A, internal BBs have integrated spindle 68mm road, 73mm mountain, 83mm downhill, 100/120mm fat bike Threaded internal bearings Square taper, Octalink, ISIS BSA or BS threaded Bottom bracket must be specced with correct shell width and spindle length
ISO threaded external No 1.37in x 24 TPI 24mm (Hollowtech II), 24/22mm (GXP), 25mm (Ultratorque/Powertorque) As above External cups   As above External cups now exist that will take 30mm spindles
Italian threaded No 1.375in (34.92mm) x 24 TPI As above 70mm External or internal     Can be prone to undoing itself because non driveside is a standard thread
BB90/BB95 Yes (Trek) 37mm 24mm 90mm road, 95mm mountain Pressed bearings with stepped BB shell Designed specifically for 24mm spindles, no 30mm option   The extra width of the BB cups is replaced with more frame real-estate
BB86/BB92 No 41mm 24mm 86.5mm road, 91.5mm mountain. Other widths may be named according to shell dimensions: 89.5mm, 104.5mm, 107mm, 121mm, 132mm Bearings pressed in cups Originally designed for 24mm spindles, but some BBs that fit a 30mm spindle are available PF41 (Hope — refers to BB shell diameter), PF24 (Chris King — refers to spindle diameter) Similar to above, but a non-proprietary version with less stringent tolerances
BB30 No (open Cannondale standard) 42mm 30mm 68mm road, 73mm mountain 6806 bearings pressed into frame with circlips to locate in BB shell Designed for specific BB30 cranks, 24mm step-down spacers available   Narrow overall width means longer spindles can be used with appropriate spacers
BB30A and BB30-83 Ai Yes (Cannondale) 42mm 30mm 73mm (BB30A), 83mm (BB30-83) 6806 bearings pressed into frame with circlips to locate in BB shell     Asymmetric BB shell which is wider on non driveside. Wider overall shell is also claimed to improve bearing support
PF30 No (SRAM) 46mm 30mm 68mm road, 73mm mountain 6806 bearings in cups Originally designed for BB30 cranks   Analogous to BB30 above, but uses pressed cups (with identical bearings) for relaxed manufacturing tolerances
OSBB (Road) Specialized 42mm 30mm 68mm Pressed 6806 bearings with circlips in BB shell Designed for specific BB30 cranks   OSBB for Specialized Road bikes appears to just be BB30. An older Pressfit 61x46mm BB appears to be obsolete
OSBB (Mountain) Specialized 46mm 30mm 73mm 6806 bearings in cups Originally designed for BB30 cranks   OSBB for mountain bikes appears to be PF30 (post 2010). An older 84.5x46mm BB appears to be obsolete.
PF30A and PF30-83 Ai Yes (Cannondale) 46mm 30mm 73mm (BB30A), 83mm (BB30-83) 6806 bearings in cups     Essentially the Pressfit version of BB30A and BB30-83
BBRight (Direct Fit) No (Cervélo) 42mm 30mm 79mm (road only) 6806 bearings pressed into frame with circlips to locate in BB shell BBRight cranks and wider   Similar asymmetric concept as Cannondale Ai, but shell is wider
BBRight (Press Fit) No (Cervélo) 46mm 30mm 79mm (road only) 6806 bearings in cups BBRight cranks and wider   As above
BB386EVO No (FSA) 46mm 30mm 86.5mm road 6806 bearings in cups Will take 386EVO cranks and traditional external BB cranks   Matches the wide bearing spacing of a BSA external BB with a large 30mm spindle
BB392EVO No (FSA) 46mm 30mm 91.5mm mountain 6806 bearings in cups Will take 392EVO cranks and traditional external BB cranks   As above
T47 No (Chris King & Argonaut Cycles) M47 x 1 30mm 68mm road, 73mm mountain Threaded cups with bearings Cross compatible dependent on spindle length Thread Fit 30i Aims to solve creaking issues of press fit systems. Essentially an oversized BSA external BB
Thread Fit 82.5 Yes (Colnago) 41mm (when shell is fitted) 24mm (30mm) 86.5mm road Threaded BB shell takes aluminium shell, which is then fitted with BB86 bearing cups Originally designed for BB86 cranksets and bearings. New integrated CeramicSpeed BB fits 30mm spindle cranks   Threaded shell can be made with better tolerances and can be replaced if it wears out. CeramicSpeed now offers a fully integrated bearing (akin to T47) that will fit 30mm spindles

We’ve also included a section on how you can (or can’t as the case may be) change between different bottom bracket standards and an explainer on why there are so many standards in the first place.