# Shimano Press Fit BB - for Pete (and anyone else)



## smudge (Jan 12, 2004)

pvd said:


> No. Shimano will win. I blame the problem on the framebuilders that don't have the common sence to go BB92 instead of BB30. It's so painfully obvious that it's discusting. Wtf?


1. sense
2. I'm far from the smartest guy here but it's not obvious to me WTF you're writing about here
3. disgusting

I can seen an argument against BB30 from a MFG point of view but BB92 and PF30 are very similar from the builders perspective. They hold different bearings in different places for different cranks. Functionally, BB92 isn't any better than a standard BB. I wouldn't make the argument that PF30 is better than a standard BB either, it just facilitates the use of different cranks.

Qualify your statements Pete.


----------



## Thylacine (Feb 29, 2004)

I think it's a case of for Steel and Ti at least, bigger BB's aren't doing us any favours. They're heavier, they don't make our frames any better or cleaner to manufacture, and few can see the benefit of having to spend an entire morning jigging up a frame on a mill so the BB can be bored to a ridiculous tolerance.

I agree with you Sean, I don't see BB92 or PF30 being any different. I also don't see either bring to us Steel and Ti guys anything of real value aside from 'keeping up with the Giants'.

With your 44mm headset for tapered forks, I see real-world benefits, but press-in BBs I don't functionally or aesthetically see any. Well actually I think the BB92 does look pretty cool, but BB30/PF30 looks out of place.


----------



## Linnaeus (May 17, 2009)

I disagree Warwick. Many of these systems can simply be reamed (by hand) after construction and don't need to be put in a mill, although that is an alternative that would work. Some of the press fit options also use the ends of the BB to locate the bearing cups and don't rely solely on the ID. The wider BB, like BB92, can help with CS/tire clearance on certain bicycles, so they do have their place. From an engineering standpoint, the bearings are better supported than they are with external cups on a traditional BB.


----------



## smdubovsky (Apr 27, 2007)

Interesting discussion.

BB92: thin plastic cup around bearing = never getting BB stuck in the BB shell again because you forget to service the bike (not sure if BB30 does this or not.) I've not used one (yet) but I would think this reduces creaking too compared to thread in?
BB92: wider set chainstays. The non-drive side one is easy. The drive side can use things like a forked plate (can't remember the builder) and still retain small crank ring clearance.
BB92: Snap to ream/face w/ hand tools (that aren't really avail yet since the US refuses to go metric)
BB92: Not applicable to most of us: superior in carbon frames since there is a wider joint avail to distribute crank forces. Can either make bike lighter or stiffer (or combination)

Warwick brings up an interesting point - weight. The shell diams are similar.
BB92 92mm wide vs BB30 68 = 35.0% more matl
Would need FEA to know how the width affects the forces to see if you could butt more and trim that difference.


----------



## HomeGrownSS (Jan 18, 2006)

BB30: blah blah blah
BB92: blah blah blah
pressfit 30: blah blah blah

SQUARE TAPER: i aint going no where


----------



## smudge (Jan 12, 2004)

For the record, the wider shells don't actually have a practical advantage when it comes to chainstay spacing and tire clearance/ring. You're still constrained by the location of the chainrings and the thickness of the drive side stay. Any problem you're going to have RE clearances, you're still going to have it if you choose to build to a BB92 vs a standard 73mm shell.

You could argue that the larger diameter shells such as the PF30 allow you to build with slightly more chainring clearance if you miter the bottoms of the stays tangent to the BB shell.


----------



## pvd (Jan 4, 2006)

BB92-

Gives a wider separation of the stays at the BB. Better.

Improves the stiffness of the rear end given the same stays.

Presses directly into carbon BBs.

Wider mount for suspension parts.

The bend is reduced getting to the stays making things easier on the tube.

The diameter of the shell is large giving a good platform for big down tubes.

Easy to make via simple ream thru

Really light shell

BB30 -

Post welding machining of a snap ring groove. HAhahahaha!

Bearings pressed directly to metal frame. Can you say Fat City! The worst system ever.

68mm wide. Dumb.

Silly big spindle. Why? Nobody knows.

Heavy a$$ shell

Totally dead standard.

PF30:

Better than BB30. That's about it.


----------



## smdubovsky (Apr 27, 2007)

pvd said:


> Easy to make via simple ream thru


The 9.3mm depth you have in your wiki, thats only the minimum depth? The plastic cups are what limit the bearing insertion?

Lynskey is who I was thinking of. One of these + BB92 could give the ultimate in clearance.


----------



## smudge (Jan 12, 2004)

pvd said:


> BB92-
> 
> Gives a wider separation of the stays at the BB. Better.


 Why? What's the benefit? Show your work.



pvd said:


> Improves the stiffness of the rear end given the same stays.


 Making this statement, without proof, is in the same ballpark as the BB30 folk claiming stiffer cranks. Prove it. I not only want you to prove your statement with some relative stiffness numbers, but I'd love to hear your take on why it would be relevant if it is true. I own two bikes built for "BB92" shells and I can't tell a bit of difference, just like I can't tell the difference between my BB30 cranks and the XTR 960's I had before. Mind you, this is FAR from me stating that there's no difference, I just can't feel it.



pvd said:


> Presses directly into carbon BBs.


 OK



pvd said:


> Wider mount for suspension parts.


 OK



pvd said:


> The bend is reduced getting to the stays making things easier on the tube.


 What's the benefit of the reduced bend? You can bend tubes all day. If done right and discounting material problems there's no issue.



pvd said:


> The diameter of the shell is large giving a good platform for big down tubes.


 no argument here



pvd said:


> Easy to make via simple ream thru


BB30 and PF30 both require a post weld bore or ream if that's your style. Most BB30 shells already have the snap ring groove in place, no additional work. WRT process, it's a wash, there's no benefit to BB92



pvd said:


> Really light shell


"really light" isn't data. A 1.5 x 73mm Paragon shell weighs 102g. King cups weigh108g. 
I'll weigh the Shimano cups later today and will edit this post. What does your shell weigh?

I know you're an intelligent guy, Pete, but spouting off a bunch of purposeless BS isn't doing anyone any good and someone out in interwebland is believing what you're writing.


----------



## smdubovsky (Apr 27, 2007)

smudge said:


> Most BB30 shells already have the snap ring groove in place, no additional work.


Can't face the shell if the snap ring grooves are already there. Do they make the shells a little extra wide to acct for that? If they make them on the +tol side, would have 0.4mm per side which is prob enough to account for the top of the shell shrinking from the welds. The snap ring grooves won't remain parallel though...


----------



## smudge (Jan 12, 2004)

smdubovsky said:


> Can't face the shell if the snap ring grooves are already there. Do they make the shells a little extra wide to acct for that? If they make them on the +tol side, would have 0.4mm per side which is prob enough to account for the top of the shell shrinking from the welds. The snap ring grooves won't remain parallel though...


No need to face a BB30 shell as the bearing has no contact at all with the face and relies solely on the ID of the shell and the snapring location as a stop. The shells are initially turned undersized with the snap ring bore sized to spec. That way, only a boring/reaming operation needs to be performed.You're right that the grooves don't remain parallel but you don't need to press the bearings far enough in to make full contact with the snap rings.

That said, and I've written this before, now that PF30 is available, I'll never build another BB30 frame. They accomplish the same thing but PF30 shells are slightly less finicky to build with.


----------



## smdubovsky (Apr 27, 2007)

smudge said:


> No need to face a BB30 shell as the bearing has no contact at all with the face


Ahhhhh. (little lightbulb above head appears)


----------



## Linnaeus (May 17, 2009)

smudge said:


> For the record, the wider shells don't actually have a practical advantage when it comes to chainstay spacing and tire clearance/ring. You're still constrained by the location of the chainrings and the thickness of the drive side stay. Any problem you're going to have RE clearances, you're still going to have it if you choose to build to a BB92 vs a standard 73mm shell.


Sean I agree with what you said for >99% of frames. However, I was purposely vague in what I posted above because it's possible to imagine a combination, albeit rare, of single chainring bike with super short CS where you can gain tire clearance with this combo. You are still correct that most frames will be limited by chainring clearance.

Wider pivot mounting on full suspension bikes is likely to be one of the most tangible benefits of this wider shells.


----------



## Thylacine (Feb 29, 2004)

_"really light" isn't data. A 1.5 x 73mm Paragon shell weighs 102g. King cups weigh108g. I'll weigh the Shimano cups later today and will edit this post. What does your shell weigh?_

SM-FCM970 Shimano BB92 pressfit cups and sleeve 71g actual.

The system _might_ be 15-20g lighter than your standard external BB setup, which isn't exactly anything to write home about.


----------



## DWF (Jan 12, 2004)

Anecdotal evidence, but we've been selling more Shimano PF adapters than all the rest. Then PF30s. I can't give BB30's adapters away and I still have about 100 sets of them. :madman:


----------



## vulture (Jan 13, 2004)

DWF said:


> Anecdotal evidence, but we've been selling more Shimano PF adapters than all the rest. Then PF30s. I can't give BB30's adapters away and I still have about 100 sets of them. :madman:


Ah, that's the data I want. What other tidbits can you clue us in on?


----------



## CurbDestroyer (Mar 6, 2008)

HomeGrownSS said:


> BB30: blah blah blah
> BB92: blah blah blah
> pressfit 30: blah blah blah
> 
> SQUARE TAPER: i aint going no where


I've still got 2 square taper BB's I've had since the early to mid 90's that still work well. Yea they are a pain in the arse to pull, but they have stood the test of time. Where's ISIS, Octa Link v1 and v2??


----------



## NorseRider (Feb 9, 2004)

It would be interesting to hear from Don in regards to any changes in the uptake pattern here.

Truls


----------

