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 (25)

1x conversion

By: on 9 October 2018
Hi, Can you please help! Have acquired a 2014 Boardman Pro 29er with 3 bolt fsa comet 2x set-up with 86mm BCD, PF30 in a 73mm shell. Running a Shimano HG 62 11-36 on rear. I have tried to find the megatooth or any other 32t fsa compatible chairing so I don't have to change cranks but they are sold out unavailable or dear as poison from italy etc. I am currently running a 3 x 9 system on my old stumpy, I rarely get out of the middle chairing (32t) and the rear cassette is 11-34, have looked at changing sprockets out on cassette to 42t as part if conversion but am I wasting my time. Do you guys have a compatible chairing available, or shimano cranks (not saints, too dear) or something! Cheers Randall

Mountain Bikes Direct Response
Hello, The FSA 3 bolt chainrings are hard to find and as you have found expensive! Your best option, in the long run, is to swap the cranks out for something that you can easily replace the chainrings on in the future. You can find all the cranks we have in the link below. The Shimano SLX or XT would be the most popular. https://www.mountainbikesdirect.com.au/parts/crank-bottom-bracket-chainguide-pedals/mtb-cranks/

BB386EVO bottom bracket derosa sk frame

By: on 31 August 2018
I've been doing a lot of research and yours is one of the only sites I could find a difference in crankset axle lengths. I recently bought a 2018 derosa sk frame whose BB opening is 46 ID and width is 86.5 mm or typically called BB386EVO. I want to buy crankset but I'm not sure all major brand cranksets are same length. I understand Q factor is Important for my frameset bc it is BB386EVO. One brand I've been looking at is Quarq which offers their cranksets for both GXP and BB30. If axle lengths are the same I could use either GXP or BB30 but basically need a BB cup that will fit the axle diameter. So if the BB fits the frame I've been looking at C-bear BB386-GXP or C-bear BB386-C (bottom bracket for BB386 with 30 mm spindle) (c-bear.com website) for the Quarq Red DZero power meter which offers GXP and BB30 options. The other BB bearings I'm looking if I use the DZero is Ceramic Speed which is EVO386 SRAM GXP and the other bearings for the 30mm spindle from Ceramic Speed is PF4630. So can I use either set up and will the axle length of this quarq crankset fit my bike with these BB. Can you tell me when the axle lengths in the new crankset change for a BB standard? Are italian threaded, English threaded, BB30, PF30, BB386 all using the same length axles in their cranksets? Thanks

Mountain Bikes Direct Response
Hi Francis, Thanks for getting in touch! Unfortunately, I'm not very up to up to date on the road side of things (we're Mountain Bikes Direct) so I won't dive too far into all the differences. If you want to run a Quarq crank, there would be no reason to run a GXP spindle. Their Red BB30 is a long spindle BB30 and is confirmed to work with BB386EVO bottom brackets. Cheers, MTB Direct.

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,

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