# About time!



## wrshultz (Feb 10, 2005)

View attachment 272181


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## RkFast (Dec 11, 2004)

I would not want to run that on my S-Works frame which has an all carbon BB. As you tighten down that collet, it puts outward pressure on the BB. One turn too many and your frame is toast. For frames with an aluminum BB, that used traditional clips, this is a nice solution.


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## PJ352 (Dec 5, 2007)

Seems to me it's just another variation of the sleeves/ adapters offered by a number of manufacturers. They all convert OSBB's to standard.

Some examples:
Wheels Manufacturing Bottom Bracket Adapters


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## davidka (Dec 12, 2001)

RkFast said:


> I would not want to run that on my S-Works frame which has an all carbon BB. As you tighten down that collet, it puts outward pressure on the BB. One turn too many and your frame is toast. For frames with an aluminum BB, that used traditional clips, this is a nice solution.


I wouldn't be so concerned about that. You apply all the strength you have in your body to the BB. That area of the frame is not fragile. You'd have to REALLY mess up to damage it with this. I'd be more concerned with slipping and creaking.


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## Praxis Works (Dec 21, 2011)

Hi everyone and "RkFast" -
Our unique Collet system _does not expand infinitely _like you have suggested. It's actually designed for both Aluminum AND Carbon frames equally. 

The Drive cup threads down and bottoms out at a machined limit to set the collets press tolerance. This also sets the drive cup right on Shimano spec. It's a very unique clever design. 
You can see more here. Praxis Works | Conversion Kit 

If any questions, just email us at Praxis!

[email protected]
Manufacturer


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## roadworthy (Nov 11, 2011)

My input is...there is a tradeoff to every single type of BB.
The factory solution for example uses fragile Delrin and now recommended to epoxy Delrin bushings in place. The factory approach is cheap however...much cheaper than other aftermarket offerings. Bushings and bearings are cheap.

C-bear and derivatives which press a sleeve in place make reversibility more difficult but not impossible. Also a C-bear sleeve is very expensive.

The Praxis bracket has very creative engineering. To me this style of BB is the future of PF-30 or derivatives. It is much more robust than press in Delrin bushings and bearings. However, again, it comes at a price. When the bearings are spent, the whole BB needs to be discarded. So it is pricey. But, the Praxis solution can be removed much more easily than a C-bear press fit sleeve. The other downside of Praxis is...it doesn't work with Campy. Campy has a 25mm OD spindle versus Shimano 24mm OD. So if running a Campy crank, a C-bear sleeve or derivative is the best approach.


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## Praxis Works (Dec 21, 2011)

....and many other BB's are coming from Praxis soon. So keep that in mind. 

[email protected]


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## roadworthy (Nov 11, 2011)

Praxis Works said:


> ....and many other BB's are coming from Praxis soon. So keep that in mind.
> 
> [email protected]


Adam,
A note I would send to your lead designer is...since you have decided to support the more narrow aka 61mm wide Specialized carbon OSBB for Shimano cranks...the leap to support Campy cranks isn't a big one. You basically have the Praxix shell halves that would work. All you need to do is have 25mm ID bearings to support Campy cranks. This should be an incremental tooling change. I believe you would have a good following with Campy. What Specialized has done is take it upon themselves to remove pressed on bearings from Campy cranks. They now offer spacers to work with their carbon OSBB with Campy cranks. But this does little to address Delrin issues. A Praxis style BB sized to work with carbon OSBB + 25mm spindle Campy cranks without Campy bearings pressed onto respective half shafts would be a good addition to your product line.

Again, the benefit of Praxis for those with a Sworks bike with carbon OSBB aka thru bore 46mm hole into carbon shell is...it can be installed and removed without detriment to the frame. As a sidebar, since Specialized now recommends epoxy of Delrin bushings to carbon shell...how does one think that removal of Delrin bushings would go? Epoxy is invasive and has to attach to the virgin carbon fiber shell. So Specialized decision to go with Delrin, once driven by serviceability has now been compromised because removing Delrin bushings once epoxied in place will not be straight forward. I haven't seen a recommended practice from Specialized outlining Delrin bushing removal once cemented in place with epoxy.
Delrin is inherently lubrice and epoxy won't stick to it as well as epoxy will bond with a carbon shell. Time will tell how easy it is to clean the BB carbon hole once epoxy is used. Type of epoxy likely matters as well.


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## PJ352 (Dec 5, 2007)

Double post - deleted.


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## PJ352 (Dec 5, 2007)

Praxis Works said:


> ....and many other BB's are coming from Praxis soon. So keep that in mind.
> 
> [email protected]


No offense, but I'm not willing to base a decision to buy a frame with BB/ PF30 based on promises of what might become available from your or other manufacturers. 

1) I may not like the design, 2) 'it' may never come to fruition and 3) the build (BB/ crankset to be used) is thought out ahead of the frame purchase. 

That said, after my OP in this thread I looked into the Praxis BB a little more and do think it offers some advantages over some of the other conversions out there.


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## DS1239622 (Mar 21, 2007)

Looks very cool. Makes me a little less nervous about upgrading from my old Roubaix Expert to one of the new higher end frames wth PF30. Starting to get the itch!


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## roadworthy (Nov 11, 2011)

Adam...a question about the Praxis BB:

- Can the bearings be serviced during the life of the BB? Is there any way to grease and/or clean the bearings to prolong their life...are seals removable to access the ball bearings?

Thanks.


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## PJ352 (Dec 5, 2007)

Sent of an email to Praxis re: the weight of their OSBB adapter and if the bearings themselves were replaceable. Here's their response:

Hi PJ, 
We don't publish our weights on any of our Praxis products. Products are always being tweaked from production to production. 
However I can tell you it's just a little more than a regular BSA threaded BB. Weight really isn't our primary focus on this product....giving a customer a rock solid BB for their Shimano crank is our goal. 

Part needs to be replaced as a unit like most BB's in the market when they wear out. Warranty is voided if product is altered from it's production state. 

THE PRAXIS TEAM 
Santa Cruz County, Ca
831-708-2161 p
831-708-2511 f
Praxis Works
Dealer Locator


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## roadworthy (Nov 11, 2011)

Thanks for sharing the Praxis response to your questions PJ.
I guess no big surprise. The sleeve/collet Praxis BB assembly will add fractional weight to the bike and Praxis wouldn't be inclined to post weight because it doesn't flatter their product. 

Second...servicability. Basically the same as DA BB or even C-bear press in integrated bearing solution. Bearings aren't serviceable. 

So with any of the aftemarket alternatives a few things:
- a bit more weight
- more expensive
- bearings can't be accessed to regrease unlike BB/PF30.

An owner's decision to opt for adapter BB's will come down to the above...balanced against the prospect of bearings making a hint of noise if not installed properly...or if Delrin bushings wear a bit over time and require replacement. BB30 bearings are pretty cheap by comparison.


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## PJ352 (Dec 5, 2007)

roadworthy said:


> Thanks for sharing the Praxis response to your questions PJ.
> I guess no big surprise. The sleeve/collet Praxis BB assembly will add fractional weight to the bike and Praxis wouldn't be inclined to post weight because it doesn't flatter their product.
> 
> Second...servicability. Basically the same as DA BB or even C-bear press in integrated bearing solution. Bearings aren't serviceable.
> ...


I drew the same conclusions, but would add that (for me) this alternative makes the prospect of opting for a Spec frame with OSBB more palatable. 

Not my ideal, but (similar to what you've offered) on balance, I like Tarmacs enough that I'd probably fall to the side of 'palatable' over going with another brand having a standard, threaded BB - and those choices are dwindling.


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## ukbloke (Sep 1, 2007)

All of these adapter products and threads have convinced me to hold onto my 2009 Tarmac Pro SL frame as long as possible! Perhaps I can wait it out until Shimano to decides on what their next standard will be?


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## roadworthy (Nov 11, 2011)

PJ352 said:


> I drew the same conclusions, but would add that (for me) this alternative makes the prospect of opting for a Spec frame with OSBB more palatable.
> 
> Not my ideal, but (similar to what you've offered) on balance, I like Tarmacs enough that I'd probably fall to the side of 'palatable' over going with another brand having a standard, threaded BB - and those choices are dwindling.


Agree. Ultimately the BB shouldn't be an overriding impediment to choosing a wonderful Specialized frame. I still disagree in priniciple to the evolution of the design playing out in front of us and many customers and bike shops being frustrated by a moving target of design. But things are now progressing. The stock design will likely now work with epoxy and loctite and if this isn't acceptable, there are aftermarket options that preclude this nuisance. Specialized makes wonderful frramesets. I believe there will be further refinement to the BB over time.


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## roadworthy (Nov 11, 2011)

ukbloke said:


> All of these adapter products and threads have convinced me to hold onto my 2009 Tarmac Pro SL frame as long as possible! Perhaps I can wait it out until Shimano to decides on what their next standard will be?


Not sure that Shimano is the veritable straw that stirs the drink when it comes to BB design. Shimano basically never relented from a threaded BB...but their cranks really convert the best to BB/PF30 because they have a straight spindle without bearings pressed on and their mechanical preload is a great design. Campy cranks are more difficult to adapt. Guess we will all see the direction of BB design. I believe it to be highly curious that two top level frames can have such divergent BB designs...take Tarmac Pro and Sworks...one with BB30 and other with narrow PF30. To me Specialized should stick with a single BB convention for their best framesets...pick one. Praxis style brackets maybe the future. They lend themselves to a through bore so Specialized should save some capital and mfg cost and forgo insert molding BB30 alloy cups. They aren't required with a collet style BB. Threads, insert molded alloy cups (BB30) and Delrin bushings (PF30) being replaced with a clever collet BB design that tightens onto the interior of a thru bore shell. If you think about it...this is much more elegant than old threaded square taper BB's of yesteryear and close to the weight of thread on DA BB cups with integrated bearings like the Praxis. So there is some light at the end of the tunnel. Progress is rarely a linear path and hopefully things will be better in the future.
Bike frames have certainly never been better and SL4 Roubaix/Tarmac are best in class.


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## bernithebiker (Sep 26, 2011)

I asked Specialized about removing the epoxied in Delrin cup if necessary, and they assured me that this was perfectly doable, but I agree, I don't sleep easy at night thinking about taking them out. 

I did use the Spesh epoxy that they gave me, so that should help, and in theory the Delrin cup should not wear and not need replacing.

Fingers crossed.


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## roadworthy (Nov 11, 2011)

Berni,
Thanks for sharing Specialized's response with the forum. A couple of comments as a guy who has designed products with Delrin.

1. type of epoxy likely matters and probably best to use the specific epoxy spec'ed by Specialized. The reason is...epoxy can be formulated for different shear strengths depending on application. Shear strength is the essential mechanical property when considering Delrin bushing removal. The good news is..when you push an epoxied bushing out with a flat implement...like a wooden dowel by tapping around the back flange edge...the delrin bushing should come free pretty easily. Epoxy bonds are weaker in shear than in tensile. Further, Delrin is a lubrice material..it is a bit waxy or slippery by nature. This reduces the hold of epoxy on it. Epoxy will stick more readily to the carbon fiber shell...which is more porous and grainy. So the bushings can be pushed out pretty easy with a bit of staccato tapping with dowel and hammer. Further...as discussed previously, once the bushings are pushed out...the hole left should be OK. The bushing is like a mold for the hole and likely any residual epoxy should not be detrimental to installing fresh bushings.

2. Delrin wear. This should be discussed in the context of how Delrin would degrade over time. With Delrin expoxied in place, wear will now...not be due to abrasion. Carbon is not a friendly surface to Delrin if the Delrin can move around. Now it can't. Plus, Delrin intrinsically has low yield strength. Carbon has high yield strength. This is why the epoxy solution works. Bonding Delrin to carbon creates a composite and uses the carbon to add a lot of strength to Delrin since it is lightly bonded. This dramatically improves the life of Delrin as it is less prone to distort. 

In summary, epoxy of Delrin to carbon shells is a good thing in terms of improving BB performance. You shouldn't have to replace Delrin very often...perhaps every couple or three riding seasons. Plus, removing Delrin bushings shouldn't degrade the BB shell.

But...there still is a downside to using Delrin to capture bearings. Delrin to me...a guy who has worked with the material...is a poor choice to hold bearings in the rigorous environment of cyclic loading. With epoxy, there will no longer be abrasive wear per se due to Delrin squirming under load...but the compressive strength of Delrin isn't the greatest. So the bushing ID bore over time due to cyclic loading can still elongate vertically. Where does the bushing material go to create an elogated bore? The material itself could compress. Also, the material can displace/protrude laterally thereby conserving overall volume however losing shape...more problematic without epoxy.

At the end of the day, I believe Delrin to be a stop gap. It isn't a robust BB solution. Either sleeving the 46mm carbon OSBB hole regressing back to a threaded BB is more robust...or...a Praxis like solution is better and more trouble free...but both are more expensive.


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## purdyd (Jun 18, 2010)

roadworthy said:


> Berni,
> Thanks for sharing Specialized's response with the forum. A couple of comments as a guy who has designed products with Delrin.
> But...there still is a downside to using Delrin to capture bearings. Delrin to me...a guy who has worked with the material...is a poor choice to hold bearings in the rigorous environment of cyclic loading. With epoxy, there will no longer be abrasive wear per se due to Delrin squirming under load...but the compressive strength of Delrin isn't the greatest. So the bushing ID bore over time due to cyclic loading can still elongate vertically. Where does the bushing material go to create an elogated bore? The material itself could compress. Also, the material can displace/protrude laterally thereby conserving overall volume however losing shape...more problematic without epoxy.
> 
> At the end of the day, I believe Delrin to be a stop gap. It isn't a robust BB solution. Either sleeving the 46mm carbon OSBB hole regressing back to a threaded BB is more robust...or...a Praxis like solution is better and more trouble free...but both are more expensive.


there are a lot of reasons Delrin (acetal) is a excellent material for holding bearings and is used as such in other things besides bikes

it is actually ideal in cycling loading situations, since it is fairly immune to fatigue (unlike aluminum)

http://www2.dupont.com/Plastics/en_US/assets/downloads/design/DELDGe.pdf

it is being loaded for extended times, that you would have to worry about, not cyclic loading

cycling loading will not cause permanent deformation unless you have high loading 

Delrin is actually stiffer in compression than tension

it does not corrode (unlike most metals), it is relatively slick, it is easy to mold, and it is relatively quiet

and that Praxis OSBB solution, uses the delrin cups for the carbon OSBB

BB30 Conversion Kit BB - 73mm

i don't think that delrin bushing for bearings for the press fit systems (specialized is not the only one to use them in bottom bracket) will go away nor should they


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## roadworthy (Nov 11, 2011)

purdyd said:


> there are a lot of reasons Delrin (acetal) is a excellent material for holding bearings and is used as such in other things besides bikes
> 
> it is actually ideal in cycling loading situations, since it is fairly immune to fatigue (unlike aluminum)
> 
> ...


Materials and designs are easily judged over time by their record. Look no farther than this forum for the book on Delrin in the context of Specialized carbon OSBB. 

I learned a long time ago not to get into protracted arguments on the web about subjects as complex as strength of materials specific to particular material properties and a given application. 

Everybody is entitled to their vote and we have made ours. Mine aligns with the track record of Delrin carbon OSBB and I will let others judge how your opinion comports with this track record.


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## purdyd (Jun 18, 2010)

roadworthy said:


> Materials and designs are easily judged over time by their record. Look no farther than this forum for the book on Delrin in the context of Specialized carbon OSBB.
> 
> I learned a long time ago not to get into protracted arguments on the web about subjects as complex as strength of materials specific to particular material properties and a given application.
> 
> Everybody is entitled to their vote and we have made ours. Mine aligns with the track record of Delrin carbon OSBB and I will let others judge how your opinion comports with this track record.


I think it rather risky to judge the performance of anything based on an Internet forum, problems tend to get blown out of proportion

You don't want to argue about strength of materials yet you keep posting about it and some of what you say is simply wrong

You also seems to have a very strong opinion about this and yet you have never owned a bike with osbb.

I understand if you like campy stuff why the osbb bb30 would be less than ideal. If I were that set on campy, I would get a different frame.


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## roadworthy (Nov 11, 2011)

purdyd said:


> You don't want to argue about strength of materials yet you keep posting about it and some of what you say is simply wrong


I have engaged you before and determined you aren't worth arguing with.
For one, it would take too much time to dissect all your inaccuracies. But moreover, a waste of time as I am not sure you can learn..lol.


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## purdyd (Jun 18, 2010)

roadworthy said:


> I have engaged you before and determined you aren't worth arguing with.
> For one, it would take too much time to dissect all your inaccuracies. But moreover, a waste of time as I am not sure you can learn..lol.


Yeah pretty much as I expected, since you can't refute anything I said, you make up excuses and hurl insults.

I suggest you read the delrin properties guide posted above.


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## jleeasc (Dec 1, 2012)

The more I read from you guys, the happier I am that I ended up buying a Specialized, even though most of what you write regarding BB's is Greek to me. I pick up bits and pieces as I go.


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## roadworthy (Nov 11, 2011)

jleeasc said:


> The more I read from you guys, the happier I am that I ended up buying a Specialized, even though most of what you write regarding BB's is Greek to me. I pick up bits and pieces as I go.


You are a wise man as you know your limitations and you are in good company with a Specialized frameset. By contrast a guy like Purdy who knows some of the buzz words, doesn't have a clue...lol. 

PJ said it pretty well. The BB shouldn't be the overriding determination of whether you should buy a Specialized frame...especially with aftermarket options that have come about to address some of the weaknesses of the stock carbon OSBB. If you are adverse to BB/PF30 however, the Roubaix Expert is still available with 10r carbon...is SL4 and with threaded BB. There are now many workarounds as alternative to Delrin as well. The point of the thread is to discuss options. What purdy fails to understand is...these options 'exist for a reason.' The reason is...Spesh carbon OSBB has a dubious track record. Therefore, some owners are willing to pay a bit more for aftermarket solutions to avert the stock BB design. C-bear for example provides two options...one is a BSA sleeve and second are press in integrated bearing/bushings...with much longer press and captured bearings which can't creep... compared to shorter press Delrin bushings with non integrated bearings...a weaker design.


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## jleeasc (Dec 1, 2012)

roadworthy said:


> You are a wise man as you know your limitations and you are in good company with a Specialized frameset. By contrast a guy like Purdy who knows some of the buzz words, doesn't have a clue...lol.
> 
> PJ said it pretty well. The BB shouldn't be the overriding determination of whether you should buy a Specialized frame...especially with aftermarket options that have come about to address some of the weaknesses of the stock carbon OSBB. If you are adverse to BB/PF30 however, the Roubaix Expert is still available with 10r carbon...is SL4 and with threaded BB. There are now many workarounds as alternative to Delrin as well. The point of the thread is to discuss options. What purdy fails to understand is...these options 'exist for a reason.' The reason is...Spesh carbon OSBB has a dubious track record. Therefore, some owners are willing to pay a bit more for aftermarket solutions to avert the stock BB design. C-bear for example provides two options...one is a BSA sleeve and second are press in integrated bearing/bushings...with much longer press and captured bearings which can't creep... compared to shorter press Delrin bushings with non integrated bearings...a weaker design.


Yep. It was actually yours, PJ's, and a few others's insight that helped me decide a few weeks ago. Alot to learn for us newbies.


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## purdyd (Jun 18, 2010)

roadworthy said:


> What purdy fails to understand is...these options 'exist for a reason.' Therefore, some owners are willing to pay a bit more for aftermarket solutions to avert the stock BB design. C-bear for example provides two options...one is a BSA sleeve and second are press in integrated bearing/bushings...with much longer press and captured bearings which can't creep....


what you continued to do is bring up the creep issue and it is not a problem for plastic under cycling loading, it is a problem under constant loading

there are many properties of plastic that make it ideal for these press fit system bottom brackets

that is why the engineers at specialized, trek, cervelo, wilier, and shimano specified that material

again, i refer you to the document on Delrin that I enclosed

i can also buy aftermarket wheels, seats, seatposts, etc. That does not make the parts on a stock bike bad

99% of these aftermarket systems are for the campy and shimano cranks which do not have a BB30 option

there are so many because there are a lot of BB30 bikes and unfortunately, Shimano and Campy don't seem interested in that standard

so in other words, all of these aftermarket adapters are not a result of the OSBB problem

The sole exception to this is one of the cbear options which replaces the delrin cup with a aluminum with a factory installed (serviced) bearing 

I have stated time and again, the external bearing adapters in these press fit systems seem less than ideal as they subject the adapter to a moment.

The point of this thread was to point out the Praxis adapater (which uses the Delrin cups in the carbon OSBB) which would appear on paper to virtually eliminate this moment (twist).

I understand that excitement and why people like shimano cranks

The reason I even to bother to post here on this subject is that there seems to be a vast amount of misinformation on the OSBB and it starts with specialized and seems to propogate into this forum.


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## roadworthy (Nov 11, 2011)

purdyd said:


> what you continued to do is bring up the creep issue and it is not a problem for plastic under cycling loading, it is a problem under constant loading
> 
> there are many properties of plastic that make it ideal for these press fit system bottom brackets
> 
> ...


This is a bike forum and honestly, I don't like to get too technical. The reason is…it goes right over the head of many…and in particular guys like you. The average bike enthusiast doesn’t need to read the following. I also am hesitant to either teach engineering on the internet..what I have done professionally…or debate it to any extreme. In other words, I can live with others like yourself and misconceptions they have based upon lack of understanding or inexperience. Design is extremely nuanced and even escapes the engineers that perform the development that live it everyday. This is obvious in the case of Specialized. The public has little chance to really understand it. I don’t have enough time to right all the wrongs stated on the internet…compromised by such diverse backgrounds. There are plenty of guys who read a spec sheet or think they understand the design or suitability for a given appllication and they don’t have a clue. Further, spec sheets are telling in terms of what they don’t define versus what they do. 

The term creep for example is often misunderstood. A guy like you will read a spec sheet for Delrin and see low creep and presume the application will be immune to it and they are wrong. An Acetal like Delrin is an engineered ‘semi’-crystalline polymer. Semi-crystalline polymers don’t have the best track record for creep performance in ‘all planes’…especially when loading encroaches upon yield depending on section modulus….aka part symmetry and section. There are many amorphous polymers available with more symmetric matrix that are less susceptible to creep in 3 dimensions because they are more homogenous. In addition, semi crystallines are sensitive to process…aka cool rate and cure time. This means…two lots of parts manufactured and machined on different days may have very different dimensional and mechanical properties. Why do I know? Because I worked with Dupont engineers and polymer chemists in the early 90’s to develop different grades of Delrin to reduce this variability. I know a lot about polymers, acetals and Delrin. 

What is often misunderstood? The distinction between creep and permanent deformation aka exceeding tensile strength. Add elastic deformation under load to the mix as well. These properties are often conflated. But it doesn’t matter which is the culprit when it comes to failure, if failure occurs. Your assertion that cyclic load can’t cause creep is wrong. It depends on the loading…especially for a semi-crystalline polymer like Delrin. If the load causes elongation in the yield zone for a particular molecule chain orientation, the part will creep or more correctly deform over time. When Delrin deforms,we know what happens in this application. It loses its press to the carbon BB shell and press to steel bearings causing bearings to shift and hence all the reports of creaking and sloppy delrin bushings on the drive side in particular. It doesn’t take a dramatic change in bushing shape or location to create noise. Noise propagation in carbon fiber is well known because of its matrix and part density. 

I won’t even get into the relationship of press interference relative to coef. of thermal expansion differences between materials or water absorption and ambient environmental aka heat/humidity conditions during manufacture, storage, assembly or usage effecting dimensional stability and therefore affecting press interference. Shrink rates during production have to be adjusted based upon environment and this is often overlooked. I have lived these relationships in development. I have performed design of experiments using Taguchi methods on these tradeoffs to determine weighting of contributing factors. 

Without seeing the stress analysis on this application it is impossible to determine whether the underlying failure mode at play is creep or loss of plasticity aka exceeding the yield strength of the material…or elastic deformation affecting bushing/bearing position. Creep can occur at relatively low stress levels and likely the dynamic at play here is permanent deformation or yield due to exceeding the tensile strength of the material…likely exacerbated by higher watt stronger and heavier cyclists. Further, bushing/bearing shift can occur without creep due to cyclic loading..staying within the elastic zone of the material where stress is relieved by unsustained cyclic loading. If the bushing deflects/compresses/distorts based upon loading…again a function of section modulus, then the bushing or bearing will lose press incrementally even though it is restored in an unloaded condition. With a torque moment applied due to crank arm, this can shift the position of bushings and bearings during cyclic loading and induce noise if not wear abrasion further reducing press. At the end of the day, no matter how crystalline polymers are, they are still elastomers which can compress under load. Adhesives such as epoxy and loctite are now spec’ed as a hedge to mitigate this. 

But again, it depends on part variation. No two lots of Delrin are the same. It may in fact be an interaction of many variables…creep and tensile only being a small subset. Yield aka high elongation based upon loading...cyclic or sustained is a function of not only the material properties of type of Delrin used but also the section modulus aka geometry of the parts involved. Where you are wrong is...cyclic loading can induce creep for acetals like Delrin and it can certainly cause permanent deformation…or part shift due to elastic deformation. Creep and/or plastic deformation based upon load path occurs at high stress levels when the section modulus is insufficient to tolerate loading based upon material properties aka tensile stength….especially if latter is diminished due to poor processing or insufficient cure time in an effort to meet aggressive production schedules. 

The last thing an average bike guy wants to read on the internet is the above…a treatise of part design…and why I never go there because it is tedious. Also the dynamic is much more complex than the above. I have no doubt engineers at Specialized have and maybe currently performing FEA’s with CAD on their carbon OSBB. But this is only the tip of the iceberg and failure modes are not just about staying within stress levels with adequate safety margin based upon worse case loading. Hopefully they are working on future BB designs which will remove the deficiencies of their carbon OSBB which no doubt are internally well documented in DFMEA and PFMEA as part of any development critical path. Also, the stress analysis likely isn’t the foundation of failure but only an ingredient aka partial contributing factor with statistical significance…bushing dimensional variation likely a major contributor due to material production.

As mentioned, I am OK with your opinion because guys like you are common on the internet. There is theory, testing in the laboratory and there is a part’s performance in the field which is the ultimate bellwether. At the end of the day, it is the performance in the field that matters. You may dismiss what is written on the internet about a particular BB performance…but I don’t. Reported failures on the internet are part of the statistical gene pool. 

Lastly, many noise isses with BB30 and PF30 are associated with poor bike set up aka crank installation. Improper bedding of bearings and inadequate crank axial preload at installation are often the root cause. In the context of BB30 and PF30, now add adhesives to the mix which bandaid a weak design and didn’t exist when both BB’s were initially released a few years back. Further…adhesion is a function of not only method, aka applicator volume and surface area, but part cleanliness to etch materials for best adhesion. Most mfr’s spec using an adhesion promoter. This adds greater variation to the set up…if this step is omitted which is often is. But, here is the issue that escapes many… improper set up…or sensitivity of set up variation is part of the ‘design robustness equation.’ If all you have are high school kids to tune a Ferrari, it likely won’t run very well. By contract the same level of sensitivity doesn’t seem to occur with external bearing BB’s…like a DuraAce BB…for the simple reason that a DA BB is threaded solidly to the shell which is more robust than any press of plastic bushings into a carbon shell. DA BB outboard bearings are captured in metal casings which is more robust than bearings pressed into plastic bushings which are spaced closer together for less mechanical leverage.


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## PJ352 (Dec 5, 2007)

roadworthy said:


> There is theory, testing in the laboratory and there is a part’s performance in the field which is the ultimate bellwether. At the end of the day, it is the performance in the field that matters. You may dismiss what is written on the internet about a particular BB performance…but I don’t. Reported failures on the internet are part of the statistical gene pool.


This, IMO, is the crux of the matter. To some extent, I find technological advances interesting, but the bottom line is... I _ride_ my bike. I don't want to study it, agonize over it breaking or having to constantly fiddle to keep it from breaking. Like my car, it's a tool - and needs to be reliable. 

And speaking of which, if any car ever required the level of care/ upkeep that we're seeing with OSBB's (and their variables), we'd find the situation unacceptable, as would the manufacturer, IMO.

Just for the record, in a previous life I was also an engineer (software), so I see the need to attend to details during the design process. In real world terms, I don't see evidence of that being done with OSBB's.


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## purdyd (Jun 18, 2010)

PJ352 said:


> And speaking of which, if any car ever required the level of care/ upkeep that we're seeing with OSBB's (and their variables), we'd find the situation unacceptable, as would the manufacturer, IMO..


do you own a bike with OSBB? My direct field experience is it is not fussy and very easy to maintain and service

I just knocked my bearings out of my Tarmac the other day and cleaned everything up. No problems at all. To me, it is easier than the threaded external cups.

Kind of reminds me of the internal routing of cables. I kind of resisted it at first, now that I have a bike with it and installed everything it seems pretty good to me.


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## purdyd (Jun 18, 2010)

One thing we do have some idea of is the forces at the pedal thanks to some of the new pedal power meters.

For instance metrigear posted this nice plot of force which shows 1000N at 460 Watts

Cozy Beehive: Pedaling Force Signatures?

Rather than rolling out the finite element analysis software, we mechanical engineers like to do some napkin calculations 

Given a 42mm diameter 7mm wide 6806 bearing, we can assume area of 42x7

Stress is Force/Area or 1000N/(.042 * .007 M2) or 3.4 MPa 

Since this is the internet and everyone puts out 1500 Watts regularly, we will just multiple that stress by 4 and get 13.6 MPa

Looking at the Delrin Data sheet, another thing we mechanical engineers like to do, we see a yield stress of 70 MPa and we are well within the working limits of Delrin

Being the doubting type that I am, i would still test it out under cyclic loading, something bike companies do a lot of. I imagine that if there really was permanent deformation of the plastic shims under loads, that would be easy to replicate.

Also, i believe we would see a lot of very angry heavy weights and delighted light weights. 

Of course maybe there is some vast conspiracy among bike companies. There seems to be a lot of that going around these days.

Delrin is lighter than aluminum and does not corrode. It also provides some isolation of the vibrations from the crank and from the frame to the crank.

the one thing I don't like about using Delrin for the last ten years, is that the black (uv stabilized) will turn a nice shade of gray after being exposed to the sun for long periods of time.

A little google search of, " creaking bottom bracket" , and you get numerous hits, even with threaded bottom brackets.

Yes, frames tend to transmit noise making it difficult to locate the real problem. A lot of supposed bottom bracket creaks turn out to be from other sources.

The distance between the shimano external bearings is greater than OSBB, but given the flexibility of the delrin cups, the principle source of resisting the moment created would be a force, on the opposite side bearing which given the geometry, would be less than that on the pedal side bearing but in the opposite direction.

The moment on the bottom bracket is the same and since the shell width is essentially the same for both systems, so is the stiffness.

that is why you see BB86, BBright, BB386 which have wider shells. 

I suppose there could be a problem with shops not installing the OSBB properly because it is too complicated. On the other hand I seem to be doing it without any problem and I am apparently an idiot who can't learn anything.

I do find it interesting that there have been reports on this forum of excessive lateral play in the crank and the report by one user of the cup spinning in the bottom bracket (presumably with the bearing inserted) and not on the other side.

In the first case I would like to know, what was the bottom bracket width?

In the second case I would like to know, did you swap cups?


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## PJ352 (Dec 5, 2007)

purdyd said:


> *do you own a bike with OSBB?* My direct field experience is it is not fussy and very easy to maintain and service
> 
> I just knocked my bearings out of my Tarmac the other day and cleaned everything up. No problems at all. To me, it is easier than the threaded external cups.
> 
> Kind of reminds me of the internal routing of cables. I kind of resisted it at first, now that I have a bike with it and installed everything it seems pretty good to me.


No, I do not. I think my previous, numerous posts comprehensively depict why. You don't have to agree with my stance, but it is what it is and your one (positive) experience and 'source' detailing the properties of delrin won't sway me. 

What _has_ swayed me (over time) are the numerous posts here, in the Felt forum, in the Trek forum and elsewhere where owners relay their negative experiences with OSBB's and the questionable feedback/ fixes they're told to employ to remedy the problems. 

FWIW, I'm not set on _never_ owning a frame with OSBB, but I _am_ willing to take it slow until I'm convinced a design'/ assembly is (to a degree) reliable and proven. Indications are, it may be awhile.


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## Doc_D (Mar 16, 2006)

So is the concern here primarily with the carbon bottom bracket or even the OSBB with the aluminum insert like a Tarmac Pro frameset?


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## PJ352 (Dec 5, 2007)

Doc_D said:


> So is the concern here primarily with the carbon bottom bracket or even the OSBB with the aluminum insert like a Tarmac Pro frameset?


I don't think there's evidence of a higher rate of frame failures with either CF or alloy OSBB's, so IMO the many variations of designs/ assemblies to fill those shells is the main source of the problem. 

Lots of talk lately about Delrin cups, but prior to their use, the alloy OSBB's with circlips had problems. And to be fair, no matter the OSBB, some problems are with the cranksets/ installations, so (IMO) there's more than one or two contributing factors at play. 

I go back to... OSBB and its variations answers a problem few had - standard, threaded BB's served most well, but technological 'advances' sell bikes. ICR being another example. 99% aesthetic, but it stimulates sales. 

To date, Praxis conversion seems to be the best compromise, but in essence, it just reverts back to enabling one to use a standard crankset. Not a bad thing, but IMO it's more a workaround (to OSBB) than a solution to its design/ assembly problems.


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## m2ber04 (Aug 13, 2012)

I'm looking to replace my crank on 2012 Tarmac Elite. I want to use a Shimano, which will require one of these adapters. Is this something a LBS can handle? Is it a pretty routine fix? It seems like these adapters are all fairly new to the market, so I have some concern with LBS expertise.


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## PJ352 (Dec 5, 2007)

m2ber04 said:


> I'm looking to replace my crank on 2012 Tarmac Elite. I want to use a Shimano, which will require one of these adapters. Is this something a LBS can handle? Is it a pretty routine fix? It seems like these adapters are all fairly new to the market, so I have some concern with LBS expertise.


I see nothing unique about the installation of either the wheels manufacturing or Praxis adapters, so with or without experience, any competent wrench should be able to handle the install.

FWIW, unless you want a permanent conversion, I'd avoid the sleeves* and stay with the adapters.

* A quick search found no results for the sleeve, so it may no longer be offered.


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