Ask a Mechanic | BB30 Crank Adaptors For English Bottom Brackets

X9 GXP CrankWelcome 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. Today’s column explains to two readers with the same basic question why BB30 cranksets won’t fit any frame bottom bracket standards that aren’t designed specifically for the BB30 standard. 

Question

I recently purchased a SRAM X7 2×10 crankset, with a BB30 bottom bracket included, that I wanted to install on my 2000 Fuji Tahoe Disc, which I know its a little old… Took the bike and crank to my local bike shop and was told the existing shell would not work, and I would need a GXP bottom bracket. He also said there may be an adaptor to make the BB30 fit. Just wondering what my options were? From: JD 

Answer

Unfortunately there is no adaptor available to make your BB30 crank work in the English bottom bracket on your Fuji. The problem lies in the length of the BB30 spindle. BB30 cranks are designed around internally mounted bearings at a nominal stance of 73mm from outside to outside on a mountain bike (road bikes are 68mm). With the 30mm diameter of a BB30 crank there is no room to mount these bearings internally. Cranks with externally mounted bearings, such as Shimano or SRAM GXP units, have a nominal bearing stance of 86mm. That is why there are no externally mounted adaptor bottom bracket bearings for your X7 BB30 crank, there just isn’t enough room for them on a spindle that short.

Shimano Hollowtech II Crankset

If you have a BB92 bottom bracket then Race Face, Shimano and SRAM GXP are your main options. No BB30.

Question

I have a new Scott Spark 940 that uses XT Hollowtech 2 crankset. I mistakenly bought an SRAM XX BB30 Crankset, is there an adapter I can buy that will let me use my SRAM XX crankset on my new bike? If not, my brother owns a Scott Spark 930 that uses SRAM S-1000 GXP PF 38×24, will he be able to use my crankset? From: Alvie

Answer

The frame bottom bracket standard that your Spark 940 uses is the threaded 73mm BSA or English bottom bracket standard. The Spark 930 frame uses the BB92 press fit standard. Both require the same XX crank, which is the GXP standard. Both cranks require a dedicated SRAM bottom bracket bearing set that is made for the GXP crank and the specific frame bottom bracket standard employed on the bike that is accepting the crankset. The spindle on a BB30 crankset is too short to fit on either bike and no adaptor exists (or could ever be made) to get it to work.

In summary, you and your brother’s available mountain bike crank options include the following: SRAM or Truvativ GXP cranksets, Race Face cranksets, Shimano Hollowtech II cranksets, and e*thirteen cranksets. Just make sure that you do not buy anything that is made for the 83mm DH bottom bracket standard or the 100mm fat bike/old DH standard.

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. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.

2014-03-05T15:57:38-08:00