Shimano BB 92 Pressfit

[rpettet]

Advantages, disadvantages, durability. Thanks

[cfox]

Not a big fan of press-fit BBs or BB30. A press fit BB is very unforgiving to the slightest imperfection in BB prep (cups will pull out, BB will creak, bearings get wrecked). The only 'advantage' I can see is for fat tubed bikes (aluminum, some newer Ti) having a larger diameter BB shell to weld to the fat down tube. Other than that, I prefer threaded BB's. With carbon, I don't see why it would be necessary at all. Pinarello manages to mold carbon around a threaded BB.

[thwart]

So why have these things taken off the way they have... ?

I mean nowadays it seems to be a significant negative for a frame (carbon, ti or aluminum, apparently not steel... yet) to be lacking a press in BB, whether it's a BB30, BB90, BB86, BB92... :rolleyes:

Is it all just smoke and mirrors?

[fatallightning]

the pfs solve many of the problems that bb30 has in terms of machining tolerance and possible ovalization or elongation from repeated insertion and removal. the pf sleeves can take up a bit of tolerance that may otherwise show up as creaks or bearing drag. and since the sleeve, and not the frame deforms ever so slightly, worries about wearing out the bearing surface can be alleviated. on carbon frame you can drop some weight as well, because you no longer need a metal insert in the bb shell, the pf sleeves ride straight on bare carbon.

[eddief]

bearings seems like a nice solid standard. so easy to install, no bullsnort extra parts. i know there are subtle reasons for the latest ones, but none of those reasons make a hoot of difference for most riders and riding purposes. i know we can't stop the freight train of "progress", but mostly it ain't so practical. i guess the same could be said about square taper, but hollowtech does seem like a good and practical evolutionary step.

[Kontact]

I think it is kind of dumb to have a BB shell wider than 68mm. BB30 and PF30 can be used with any type of crank system out there with the appropriate adapaters. BB92 will only work with cranks designed originally for outboard bearings, so you are stuck with cranks with little heel clearance that are heavier than they need to be. A big fail in my book.

[jamesutiopia]

My knees had hoped BB30 or some analog would enable narrower cranksets than are available for external cups (lower "tread" or "q-factor") with a 1x10 plus bailout ring setup (basically a compact double with a narrower chainline, because I never ride the small ring + small cog combinations).

Instead it looks like the existing external cup cranksets have simply been adapted (with spacers) to work with BB30/PF-whatever, yielding exactly the same tread as external cups (e.g. unambitious 145mm wide doubles).

If narrow BB30 cranksets existed I would buy more than one new frame for this feature alone. For now I hoard Shimano FC-7400 (http://konstantin.shemyak.com/wiki/images/6/61/QFaktor-shimano.pdf) (pedal eyes seem to crack), Mavic 637 (http://www.bikepro.com/products/cranks/mavic.html) (still have a NOS set waiting for the right build; have a long life with some judicious filing of a stress riser where arm intersects spider), and Ritchey Logic cranksets (http://www.bikepro.com/products/cranks/ritchey.html) (excellent design that works great as a double too)

[Kontact]

My knees had hoped BB30 or some analog would enable narrower cranksets than are available for external cups (lower "tread" or "q-factor") with a 1x10 plus bailout ring setup (basically a compact double with a narrower chainline, because I never ride the small ring + small cog combinations).

Instead it looks like the existing external cup cranksets have simply been adapted (with spacers) to work with BB30/PF-whatever, yielding exactly the same tread as external cups (e.g. unambitious 145mm wide doubles).

If narrow BB30 cranksets existed I would buy more than one new frame for this feature alone. For now I hoard Shimano FC-7400 (http://konstantin.shemyak.com/wiki/images/6/61/QFaktor-shimano.pdf) (pedal eyes seem to crack), Mavic 637 (http://www.bikepro.com/products/cranks/mavic.html) (still have a NOS set waiting for the right build; have a long life with some judicious filing of a stress riser where arm intersects spider), and Ritchey Logic cranksets (http://www.bikepro.com/products/cranks/ritchey.html) (excellent design that works great as a double too)
James, the Q-factor may or may not be the same, but real BB30 cranks have noticeably greater heel clearance.

[jamesutiopia]

James, the Q-factor may or may not be the same, but real BB30 cranks have noticeably greater heel clearance.

Encouraging observation. Perhaps things have improved since 2009 (http://www.velocipedesalon.com/forum/f2/bb30-low-qs-requesting-info-7252.html)

[Kontact]

Encouraging observation. Perhaps things have improved since 2009 (http://www.velocipedesalon.com/forum/f2/bb30-low-qs-requesting-info-7252.html)
Well, heel clearance is a different beast than Q.

Q is pretty much driven by chainline and the thickness of the crank arms. Nowadays everyone uses about the same chainline of 43.5 for a double, which puts the outer ring at 46mm (though most I've measured lately were closer to 48. With enough clearance for the front derailleur outer cage and an arm thick enough to be hollow or made of carbon, getting much below 145mm is pretty difficult. The 138mm Mavic listed in that thread has a very thin crank arm, and an unknown chainline.

So while BB30 is narrower in the center, unless someone decides to build special a low Q crank for BB30, they are going to remain in the mid-140 range. BB30 is primarily a weight saving/stiffer system, so going to solid aluminum to make the arms thinner is going to go against the grain for BB30 makers/marketers. However, it would be interesting to measure Q without the pedal washers most companies include - that would probably buy you 4mm.

BUT, a BB30 frame will accept an adapter to run a Mavic or DA 7410 crank and BSA BB, which do have small Qs. And BB92 will never allow that to happen. Old cranks can be "upgraded" to 10 speed standards with new rings, so there really is no reaon that anyone with a BSA or BB30 frame can't mount a narrow Q crank by simply going old school.

[jamesutiopia]

BUT, a BB30 frame will accept an adapter to run a Mavic or DA 7410 crank and BSA BB, which do have small Qs. And BB92 will never allow that to happen. Old cranks can be "upgraded" to 10 speed standards with new rings, so there really is no reaon that anyone with a BSA or BB30 frame can't mount a narrow Q crank by simply going old school.

This would seem to be a potential benefit of BB30/PF-narrow vs PF92...

My uninformed suspicion is that the pervasive use of carbon rear ends has made chainstays wider than they were with steel or Ti, so perhaps accommodating super-oversize carbon chainstays is what drives the wider Q-Factor of modern cranks? Have not had enough CF frames to really know if this is generally the case, or was unique to my CF frame.

Either way, apologies for the thread drift

[rpettet]

I purchased a Breezer carbon MT bike with the BB92 hence the original question. The wider BB allows for a 2.2 tire to fit between the shorter chainsays. Non drive side stay is somewhat thicker than the drive side. Who knows if there is any benefit to this, likely just marketing.

[Kontact]

This would seem to be a potential benefit of BB30/PF-narrow vs PF92...

My uninformed suspicion is that the pervasive use of carbon rear ends has made chainstays wider than they were with steel or Ti, so perhaps accommodating super-oversize carbon chainstays is what drives the wider Q-Factor of modern cranks? Have not had enough CF frames to really know if this is generally the case, or was unique to my CF frame.

Either way, apologies for the thread drift
I don't think it is the frame, just the arm thickness that drives Q. I haven't seen any carbon frames that looked like crank clearance would be an issue.