Which Bottom Bracket and Cranks Do I Need?

 

Bottom Bracket and Crank Standards are often a source of mass confusion. So let’s jump in and figure out what’s going on down there!

 

Bottom Bracket or BB as they are commonly known, refers to the bearing system that your cranks spin on. Bottom Bracket Shell refers to the part of your frame that your bottom bracket is installed into. There is a multitude of different designs that are employed in the hope of creating a stiffer,lighter and stronger frame. In this article, we're going to stick to the commonly used current BB standards.

 

Types of Bottom Bracket Shells

Threaded (BSA) - As the name implies, the frame is threaded, and a cup screws into the frame. With the newer 2 piece style cranks, these are often called external bottom brackets as the bearing is housed outside the frame. Originally designed for either 24mm spindles or GXP spindles, however you can now get BBs to suit 30mm spindles too.

Pros: Very simple to maintain and install. Can be done with very basic tools found here.

Cons: Slightly heavier and slightly more expensive to manufacture than pressfit systems.

 

Press Fit BB92 - Uses the same sized bearings as a threaded BB, but the bearings are housed in a plastic cup that is pushed into the frame. The bearings sit inside the frame. Originally designed for either 24mm spindles or GXP spindles, however BB's are now available to suit 30mm spindles too.

Pros: Lightweight, BB Shell is wider so downtubes can be made wider and potentially stiffer. 

Cons: More expensive press tools are required to install like this. To remove the BB it's not uncommon for it to be damaged and require replacement. If the frame tolerances aren't tight enough the cups can creak in the frame.

 

Press Fit 30 (PF30) - Uses the same sized bearings as the superseeded BB30 design, but the bearings are housed in a plastic cup that is pressed into the frame. Originally designed for 30mm spindles, however adaptors are available to suit 24mm and GXP spindles.

Pros: Easily fits all spindle types, still very light

Cons: More expensive press tools are required to install like these. To remove the BB it's not uncommon for it to be damaged and require replacement. If the frame tolerances aren't tight enough the cups can creak in the frame.

 

 

 

Cranks, Crankset or Crank Arms refer to the arms that your pedals screw into.

 

Types of Cranks

 

 

One Piece: Very old design, only used on very cheap bikes. Once piece refers to the crank arms and axle are all made from one piece.

Two Piece: The current designs. Light and Strong. 2 piece refers to the one of the cranks and spindle being together as one piece and a separate arm that bolts to it.

Three Piece Design: An older design. Doesn't have the reliability of two piece designs. Called Three piece as there is 2 crank arms and a separate spindle, so 3 components.

 

In this post, we’re just going to focus on the current 2 piece crank systems.


Types of Crank Spindles (Axles):

24mm Spindle - This is the most common type made popular by Shimano’s Hollowtech 2 system over 10 years ago. These use a straight steel spindle that is 24mm in diameter. Predominately used by Shimano, RaceFace

 

 

GXP Spindle - These run a 24mm Steel Spindle that steps down to 22mm at the non-driveside bearing. Predominately used by Truvativ / Sram.


 

 

30mm Spindle - A straight aluminium spindle 30mm in diameter. Used in Sram's BB30/PF30 Cranks, Race Face's Cinch Cranks, Rotor Cranks and Hope Cranks.

 

With 30mm crank spindles it's important to note that they do come in different lengths. For instance SRAM make spindles that are either 95mm or 101.5mm from the tension adjuster to the end. The short spindles will only work in a BB30/PF30 BB Shell. 


Comments (23)

Frustrated

By: on 15 June 2018
I have an older Cannondale with 3 piece cranks. I changed the old bb to an xtr bb93. No I can’t find anywhere that has a 24mm spindle. Help!,.,

Mountain Bikes Direct Response
Thanks for checking in! If you're after a 24mm spindle to match that BB, the options below are great: https://www.mountainbikesdirect.com.au/shimano-slx-fc-m7000-1x11-crankset https://www.mountainbikesdirect.com.au/shimano-xt-fc-m8000-1-1x11-speed-crank-arms Please note that both are 1x - single chainring up front. Cheers, MBD

Mega Exo BB to Shimano BB (Threaded)

By: on 8 June 2018
Will a shimano hollowtech bottom bracket (threaded) can be used on a FSA Comet modular Crankset?. I can't seem to find mega exo bb here in our country. All I know is that their spindle diameter are both 24mm. So in theory it should fit. Thanks.

Mountain Bikes Direct Response
Hi mate, judging from what I can see online, the Comet should fit perfectly in any 24mm spindle BB.

Hope 30mm cranks and B.B. comparability

By: on 15 May 2018
Looking at getting a Hope 30mm crankset to fit my 73mm BSA frame. Is the Race Face Cinch BB compatible? £90gbp for a B.B. seems excessive even by Hope standards.

Mountain Bikes Direct Response
Thanks for checking in! Hope does have a disclaimer on their site saying they can't guarantee that non-Hope BBs will work. However, in our experience, you shouldn't have any issues. Unfortunately, we are sold out of Race Face 30mm BBs at the moment. We'll be bringing some more in ASAP. Cheers,

Crank spindle length

By: on 15 May 2018
I'm still a little bit confused. So, it is impossible to use crank for bb30/pf30 and for bb92? I understand that in bb92 (like 86,5 and 92) i ti will fit. But i cant put it into bb30/pf30

Mountain Bikes Direct Response
Hi there, Generally, a BB30 or PF30 crankset will have a 30mm spindle, but there are some models of BB or adaptor cups that will allow the use of a GXP or 24mm spindle with these BB types. You can also get a BB92 bottom bracket that will accept a 30mm spindle such as the ones made by Raceface. If you shoot us through an email to help@mountainbikesdirect.com.au with the details of your bike (make/model/year/frame material etc) we can answer any specific questions you might have about it! Cheers, Rob

Crank spindle lenght

By: on 11 May 2018
Hi, I've got some question about spidnle length, Is it the same for bb92 and bb30? Shell widht for bb92 is either 86,5 and 92, and for bb30 or threaded is 68/73 mm, so can i use the same crank for all types of bb. Im just asking about spindle lenght. Thanks Kornel

Mountain Bikes Direct Response
Hi Kornel, Thanks for checking in! It can definitely be pretty confusing with all the different 'standards.' Regarding BB92 - the 86.5 is the typical road width whereas 92 is the standard mount bike width. DH bikes will us an even wider shell. BB92 bearings sit inside the frame and threaded are external. This means using the same 68/73mm crank between the two standards (92mm shell) is extremely easy. BB30 is a little more confusing. Often mixed up with PF30 - BB30 bearings press straight into the shell and PF30 bearings are pressed into cups which are then pressed into the frame. Using the same crank requires the use of adaptors or conversion BBs. Hope this helps. -MBD

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