Really, BSA-47… another new bottom bracket standard? Bombtrack has always told us they were proponents of easy-to-use, reliable bottom brackets. They started to transition  to T47 bottom brackets for all of their new and updated frames two years ago. But now they say that “while the [T47] standard is working just great, we have constantly been working on refining that critical area.”

So what comes next?

Bombtrack moving to new BSA-47 threaded BB standard?

Bombtrack BSA-47 BB, new threaded bottom bracket standard concept
c. Bombtrack

A more detailed analysis of the forces that come into play in the crankset-to-frame interface at the bottom bracket revealed to Bombtrack engineers that it was clear that “there is no real symmetry there, so specifying the same bearing sizes on both sides might be easy to do, but does not max out the real potential in frame and BB shell design.”

Lower non-driveside stresses allowed for a smaller set of bearings to save space and boost mud clearance, while the doubled up on the higher stress driveside. That resulted in Bombtrack picking the threaded best of both worlds, a 68mm wide tapered bottom bracket shell with a threaded BSA cup on the left non-driveside and a threaded T47 cup on the right driveside.

Bombtrack call the open standard: BSA-47.

Bombtrack BSA-47 BB, new threaded bottom bracket standard concept, open standard dimensions

Bombtrack says…

The advantages over current straight T47 or BSA shells are manifold:

  • The same BB shell can both be used for symmetric and asymmetric frame designs by simply swapping the T47 side for an externally or internally housed bearing.
  • With the smaller diameter on the non drive-side there is more room for chain stay attachment and can help to increase tire clearance on a frame design as compared to a standard straight BB, all else being equal.
  • Standard BSA and T47 cups can be used, so you can choose from the proven standards.
  • Almost any crankset is compatible.

Bombtrack prototype BSA-47 crankset

Bombtrack BSA-47 BB, new threaded bottom bracket standard concept, prototype crankset axle

Bombtrack say they are even in the early days of development on a unique new crankset specifically designed to take most advantage of the new BSA-47 bottom bracket system. In an effort to avoid what they call the all-too-common “paper-thin bearing cups” that are needed to fit a 30mm spindle through a conventional BSA BB shell, they have a new split-spindle design concept – made of steel with a 25mm diameter on the left side (blue) and aluminum for the 30mm right side spindle (green).

Bombtrack says the two halves of the bottom bracket spindle/axle will be joined together in the middle, “connected with a single M10 bolt, similar to the Hirth joint you see on Campagnolo cranks, but this design features a standard square taper.”


When will it be available?

Bombtrack new BSA-47 threaded bottom bracket standard prototype

Bombtrack says, “Currently we are in the final testing phases, but everything is working out even beyond our expectations and we confident that we can make the switch to BSA-47 on all of our frames as early as MY23.

Did we already spot a Beyond+ test mule prototype, and not even notice it? Or maybe that bike is just covered with a bunch of mud? (click to zoom, above.) Who can really tell these days?


April Fools! Sometimes hard to distinguish facts from fiction, this seems to be at least partly fake news. The cycling industry pulls our legs, sometimes we pull along a bit too all in good fun, and we all can be entertained. Now back to your regularly scheduled, real new tech stories


  1. wow, as a cr-moly frame manufacturer, I’m not impressed. BSA is fine, threaded DUB is fine, there’s no reason for another standard. I can’t see the crankset suppliers investing in this standard.

  2. makes perfect sense, just like a tapered head tube is stiffer where it needs to be a tapered BB can provide a real performance boost tailored to the actual forces in the system.

    don’t know why they need the unique crank tho, a DUB spindle would fit both standards quite well

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