Bottom Brackets Demystified: A Guide to Adapters

Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at daniel.slusser@artscyclery.com.

I have been getting a slew of questions regarding bottom bracket standards, adaptors, and the like. To be honest, it has been a real headache for me and our customers. To help ease the pain that I suspect many of you share with me, I have a couple common questions listed below followed by a brief list of common adaptors and parts I have experience using with success.

With any luck the industry will start working together to come up with fewer standards we can all share rather than the mess of competing standards we have today. If not, we will just have to follow the example of Look and have each frame manufacturer come up with a frame specific crank. I would prefer the former to the latter, but realize the chances of the former actually happening are slim.

Remember: Even though SRAM and Shimano cranks both use 24mm spindles, they are very different. SRAM GXP spindles step down on the non-drive side. The other key difference is that SRAM GXP cranks are tightened down on the non-drive bearing only, while Shimano cranks press on the outer race of both bearings. These differences require different adaptor solutions in nearly all cases. Make sure you have the right adaptor for your application especially if it is for SRAM. Lastly, I advise home mechanics to avoid SRAM GXP crank adaptors that require installation of a sleeve to be installed on the stepped down GXP spindle to work in a bottom bracket or adaptor that is primarily made for Shimano applications. This type of adaptor is trickier to install and is not worth the headache, especially if you don’t have a lot of mechanical experience.

Question: I’m trying to mount a Shimano Dura-Ace crank on a BBRight equipped Cervelo S5. Is there an adaptor or specific bottom bracket available to make it work? From: Scott

Cervelo S5 Team Ultegra Di2 2012

Enduro (ABI) makes an adapter to mount Shimano cranks to the BBright frame design on the S5.

Answer: Enduro (ABI) makes the adaptor you need. It is a press-in reducer type that uses the existing BBRight/PF30 bottom bracket and just reduces the bearing bore down to 24mm while adding the extra width needed for a Shimano crank. Unfortunately this part is only available from Cervelo at the moment, which means you need to work with an authorized Cervelo dealer to get them (fortunately, we are an authorized dealer). Hopefully it will be available from distributors soon.

Question: I have a PressFit 30 bottom bracket on my 2012 Specialized Stumpy hardtail and I want to install SRAM X9 GXP cranks on it. I know I need some sort of SRAM specific adaptor but I can’t find anything except adaptors that are made for Shimano cranks. Is there anything out there, or do I just need to fork out for a BB30 crank? From: Jack

This adapter allows you to use a standard BSA (GXP or otherwise) BB in a PF30 frame.

Answer: The best solution I have found so far for your situation is made by SRAM. It is a SRAM PressFit 30 to English Bottom Bracket adaptor (manufacturer’s part# 00.6415.049.010). This is a neat adaptor because it works for any PressFit 30 frame that is 68mm or 73mm wide. It uses standard English outboard bearing bottom bracket cups that thread into the adaptor. Just follow the included instructions for the correct number of spacers and the location of the wave washer for your specific application.

This adaptor also works for Shimano cranks, just use the outboard bearing bottom bracket spacers you would normally use in a frame with a standard English bottom bracket width that corresponds to your PF30 bottom bracket shell width (i.e. 68 or 73mm).

Below is a list of reliable adaptors for common applications:

Adaptors for BB30 frames to use 24mm spindle cranks

Rotor BB30 to BB24 Converter Bottom Bracket – This is a Shimano specific adaptor that places the bearings outboard of a BB30 frame in order to work just like a normal English bottom bracket would with outboard bearings threaded into it. However, with this one the bearings are pressed into the adaptor so no additional bottom bracket is required for use with this adaptor. This makes it a very stiff adaptor solution for BB30 frames.

Wheels Manufacturing Bottom Bracket AdaptorsThese adaptors are perhaps the easiest to use. They simply press into a standard BB30 bearing and reduce the bore to 24mm while extending the overall width to meet the standard required for Shimano, Race Face, FSA, or Rotor 24mm spindle cranks designed to work with English bottom brackets. SRAM GXP specific versions are also available.

Adaptors for PressFit 30 (PF30) frames for use with 24mm spindle cranks

SRAM PressFit 30 to English Bottom Bracket Adaptor (manufacturers part# 00.6415.049.010)–This is a neat adaptor because it works for any PressFit 30 frame that is 68mm or 73mm wide. It uses standard English outboard bearing bottom bracket cups that thread into the adaptor. Just follow the included instructions for use with a 24mm SRAM GXP crank for the correct application of spacers and wave washers.

For use with a Shimano crank, just use the spacers you would normally use in a frame with a standard English bottom bracket width of either 68mm or 73mm.

With these adapters, you can use any steel 24mm or GXP crank on any BB30 or PF30 frame.

Wheels Manufacturing Bottom Bracket AdaptorsThese adaptors are very easy to use for both Shimano and SRAM GXP cranks. They simply press into a standard PF30 bottom bracket bearing and (for Shimano specific adaptors) reduce the bore to 24mm while extending the overall width to meet the standard required for Shimano, Race Face, FSA, or Rotor 24mm spindle cranks designed to work with English bottom brackets. Wheels Manufacturing’s SRAM GXP adaptors function the same way but step down on the non-drive side to work with the smaller diameter GXP spindle interface.

The best adaptor that Wheels Manufacturing makes actually isn’t an adaptor, it is an adaptor bottom bracket. The Wheels Manufacturing PF30-24mm Outboard Bottom Bracket threads together at the center for a fit that is as solid and stiff as possible.

Adaptors for BBRight frames for use with 24mm spindle cranks

Enduro (ABI) makes an adaptor that is a press-in reducer type that uses the existing BBRight/PF30 bottom bracket and just reduces the bearing bore down to 24mm while adding the extra width needed for a Shimano crank. 

Wheels Manufacturing also makes similar press-in reducer BBRight bottom bracket adaptors to work with both Shimano style 24mm spindles and SRAM GXP.

Hopefully this post has done more to clarify the issue at hand rather than confuse. But if you are still scratching your head, please feel free to shoot me an e-mail or post a question on our Facebook wall.

Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly University. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.

2015-03-20T13:07:56-08:00