We know, there’s no such thing as a stupid question. But there are some questions you might not want to ask your local shop or riding buddies. AASQ is our weekly series where we get to the bottom of your questions – serious or otherwise. Hit the link at the bottom of the post to submit your own question!
Ah, bottom bracket standards. While some see the opportunity to squeeze every last bit of performance out of a frame and crankset, most see it as an endlessly confusing parade of standards designed for no other purpose than confusing the consumer.
Regardless of how we got here, we’re now faced with question of what cranks fit which frames. Something made even more confusing with the proliferation of 30mm spindles. Which brings us to today’s questions, “How do I get a BB30 crank in BSA bottom bracket?”
That was sent in recently, and it’s the exact opposite of our very first AASQ – how to fit a BSA crankset into a BB30 frame. Maybe you already own a BB30 crankset, or perhaps bought the wrong one, whatever the reason, it’s a valid question. A major source of confusion lies in the name itself – all BB30 cranksets have 30mm spindles, but not all 30mm spindle cranksets are BB30. BB30 specifically refers to a standard that used 68 or 73mm shells with a 42mm inner diameter meant to press 6806 bearings directly into the frame which had a 30mm internal diameter.
Before the introduction of BSA30, there really wasn’t an answer to this question. As you may recall from AASQ #1, BSA refers to the Birmingham Small Arms company which established the threading standard for threaded bottom brackets – 1.370/1.375″ x 24 TPI threads and a left hand thread on the drive side cup. These days, BSA, ISO, and English are used interchangeably to refer to what is now considered to be a standard threaded bottom bracket shell or bottom bracket.
Most outboard bottom brackets for BSA threaded frames originally were designed around cranks with a 24mm spindle. But with the introduction of BSA30, companies introduced an outboard cup with a larger diameter bearing that would allow 30mm spindles to pass through the bottom bracket and the bottom bracket shell.
But before you go buying a BSA30 bottom bracket, there’s still some compatibility to worry about. While both standard BSA threaded frames and BB30 frames have 68mm shells for road bikes, the external bearings of the BSA frame when used with an outboard bottom bracket would render a standard BB30 crankset’s spindle too short to use with a BSA30 bottom bracket.
To complicate things further, there are oddballs like Cannondale’s BB30a, Specialized’s OSBB, and Cervelo’s BBRight that are all some variant on the BB30, but with different widths. Depending on where your crankset came from or what standard it was meant for, it could have a different spindle width.
To get back to the original question, the first thing you need to do is identify which crankset you are working with and how long the spindle is (the part that connects the two crank arms through the middle of the bottom bracket). According to Wheels Manufacturing (who makes all kinds of bottom bracket adapters, bottom brackets, and accessories), in order to use their threaded to 30mm bottom bracket, you’ll need at least 104mm of spindle length. That’s measuring from the inside face of the crankarm (without any spacers) to the end of the spindle. Note that given the number of bottom brackets and frame tolerances, you’ll probably have to use a combination of spacers to ensure the proper fit. If your crank spindle is less than 104mm, well then you’re probably out of luck – unless your spindle can be replaced.
Some cranks, like the Race Face Cinch system, make it extremely easy to swap spindles. Just unbolt the current, and then reinstall the longer option. If the crankset doesn’t have a replaceable spindle, then you’re most likely going to be shopping for a new crank. While it’s technically possible to press the spindle out of some cranksets and replace it with something else, for most riders it’s not worth the time, effort, and expense involved.
Long story short, start by measuring the spindle. If it’s 104mm or longer (or has an easily replaceable spindle), buy yourself a BSA30 bottom bracket (don’t forget the special tool needed for the install!), and enjoy your 30mm spindle crankset on your BSA frame.
Got a question of your own? Click here to use the AASQ form, or find the link under the Contact menu header up top anytime a question pops into your mind!