Apparently PF30 shell is 4mm larger in diameter than BB30 (46 v. 42) which may be a way to allow for a larger spindle system. The issue seems to be that you need enough space for the bearings to have decent size balls which won't get worn/crushed too easily. Seems a convenient way to add 4mm or more to the spindle size. Has anyone tried it?

A search didn't pull any info.

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Praxis?
http://www.bikeradar.com/news/article/s ... xis-30017/

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Technical Artisans

Hi guys...
Just wanted to chime in as I saw your conversation.

Bike Rumor did a nice overview of our TURN brand cranks that will be using a 35mm Carbon spindle...
Have a read... http://www.bikerumor.com/?s=Praxis

The Praxis M35 BB system is just that. We wanted to design a BB system that worked in current OS standards and not create another standard...as we know how much of a headache that topic is. 35mm is a more manufacturing friendly size for using alternative materials (like carbon) for the spindle and push the stiffness needle up.

We're in deep dev on it now, with hopes to have the TURN carbon road crank out in by Interbike next year.

Hope that gives some insight..
-Praxis

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Praxis Works
Manufacturer
Santa Cruz County, CA

Unless you push the bearings outside of the shell on some of the 'rough' press fit frames you should house them in cups of some description IMO. If the cups are 2mm thick, you end up with a 42mm OD bearing surprise surprise. A few ways I can think of that get around 'cups' to house the bearings internally and allow you to use the full 46mm, but they still add other components to the BB assembly and require more fine finish work than many mass produced type press fit shells receive I imagine. By 'rough' I mean that some press fit shells (not all) don't seem like a good place to be pressing bearings into on their own, maybe just something to think of from a production standpoint

Housing the bearings outside of the shell is a pretty good way of going about it though so hopefully M35 becomes much more common for those who don't need a super narrow Q - It really seems to make sense on MTBs where that's somewhat governed by tyre size more so than on a road bike.

my understanding of PF 30 was that it addressed wear issues sometimes associated with BB30 systems. the additional space allows for a plastic sleeve between the bearing and the shell that prevents the shell from wearing when bottom brackets are replaced.

Since I've only had to re-install 1 BB30 system with no issues afterward I guess you could use the extra space for a larger spindle and different pressed in bearing.