Praxis Works Conversion Bottom Bracket for Specialized OS Frames


by Jim Weaver, Service Manager, Fit Werx, VTPraxis Works Conversion Bottom Bracket

Last winter, I posted an article about the Praxis conversion bottom bracket and you can read about the general design of these helpful bottom brackets on that post.  Shimano crankset spindles are built at 24mm and are thus too small and too long to fit in a BB30 or PressFit 30 bike without the use of some sort of adapter or converter.  The Praxis BB30 Conversion Bottom Bracket allows a bike owner to use a Shimano crankset on a bike with either a BB30 or PressFit 30 bottom bracket. The Praxis Works Conversion Bottom Bracket is held in the frame by a threaded housing that connects the two sides of the bottom bracket together.   This threaded design means a tighter and more fixed interface with the frame and thus the Praxis Works Conversion Bottom Bracket works better than any other type we have seen here at Fit Werx in BB30 bikes as it eliminates several problems that are, unfortunately, common with BB30 and PressFit 30 designs.  These issues include the following:

  • BB30 designs are more prone to creaking as the bearings are held in place by pressure.
  • Pressing bearings into a BB30 frame, or pressing the PressFit insert, compresses the bearings to some extent.  As a result, to varying degrees depending on how exact the frame tolerances, BB30 and PressFit 30 bottom bracket bearings will not spin as well as the old external bearing designs.
  • Exposed BB30 style bearings frequently are not sealed as well as the old style threaded bottom bracket and are therefore more prone to contamination.
  • If you install a Shimano crankset in a BB30 or PressFit 30 frame, the basic adapters that are generally available don’t address any of the creaking issues and can actually add another variable into the equation.

Thankfully, the Praxis Works Conversion Bottom Bracket all but eliminates these problems.  However, because manufacturers have become so intent on creating their own bottom bracket designs, the Praxis conversion bottom bracket only works in some bikes and not in others.  Until recently, the listing of brands that it did not work in included Specialized OS.  That has recently changed.

The Praxis conversion bottom bracket is a great solution to a variety of problems, while allowing you to get the great shifting performance of Shimano cranks.  With the new Specialized OS Praxis Conversion Bottom Bracket, from the Shiv to the latest Tarmac, now we can adapt Specialized bikes to use a Shimano crankset.  While the Specialized crankset is a decent product,  it is very hard to beat the new Dura Ace 9000 and Ultegra 6800 cranks for quality of shifting, stiffness, or aesthetics, for that matter and they are also compatible with Stages Power Meters.   We recently installed a new Ultegra 6800 crankset with a Stages Power Meter into a Shiv for an athlete with the Praxis conversion and it installed easily and had freer spinning bearings than the ones that came from Specialized.  The threaded compression of the bottom bracket also virtually eliminates the possibility of creaks due to movement of bearings in the bottom bracket shell.

If your Specialized has developed a bottom bracket creak that nobody has been able to permanently fix or you want to use a Shimano crank based power meter, Praxis conversion bottom bracket in combination with a Shimano crank is a very good solution.

If you have questions or would like to buy a Praxis Works Conversion Bottom Bracket or have one installed on your bike, please call or email us.

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