I was thinking, that's always a problem.

So lots of carbon frames have press fit Bb's and some complain of creaking. There are some ways to attempt to fix this.

Other frames have a threaded BB, usually BSA. This should be perfect. Then I got the thought that it's a threaded BB shell bonded to the carbon frame. Probably with epoxy and hopefully keyed in place while the carbon is still soft/wet.

Has this ever been a problem? A threaded BB shell that has caused creaking due to an imperfect bond to the frame?

No brands or models, just a crazy thought.

People have done and still do that. We had a customer whose BB shell literally turned to powder due to extreme corrosion. Hopefully just via sweat and maybe drink mix but it is a tri bike so probably a bit of pee as well. However I don't hear of issues happening often with creaking though dissimilar materials aren't ideal.

I think the trick to everything is super high tolerances from frame manufacturers and also BB manufacturers as well as using thread together BBs. Or just don't use carbon. Steel is real, Ti is fly and Aluminum simply doesn't rhyme easily so let's eliminate that. Wood is good but unfortunately Renovo while super beautiful didn't have the business side down well from what I hear.

I have got to wonder thinking about this why Headsets are generally not problematic but bottom brackets are and why can't we do a headset on its side, basically?

I have a PF30 alloy shell in crabon frame and it is loose on the drive side. So I imagine BSA could as well.

scott s.
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I have 3 steel bikes. I also don't base my purchases on rhymes.

If you and the other response are representative of the whole, it sounds like BB shells are glued into the frame after it's cured, rather than put in as a part of the initial layup. I understand why from a manufacturer standpoint but it seems unreliable.

I've had two carbon frames with BSA BB's: Trek 5200 and Ridley Excalibur. Never an issue with either one.

In the airplane world, we put all our holes on the airplane structure after the cure process is complete. It largely has to do with the way the material matrix compresses & takes final shape as the resin melds with all the other layers in the layup during cure. We use quite a high pressure of some common gasses (not "air") & a lot of heat to ensure everything is squeezed into place hard/dense enough in to a solid cohesive substrate.

A metal bushing installed prior to cure would have a different rate of thermal expansion/contraction than the composite. & effect manufacturing consistancy, structural integrity and at best would cause unpredictable performance.

Though, I suppose once the structure has been removed from the autoclave it wouldn't matter what kind of bushing is installed. So long as the circumference of the bushing was large enough to spread the load over a large enough area of structure, & it was both resin bonded & an interference fit...A BSA standard bushing is as good as any as far as I'm concerned.

Nearly everything we do with CFRP that is structural in nature is interference fit, but by way of a method I am unsure is proprietary information or not. So I'll not disclose the how of how we do it. Nevertheless whatever bushing or interface is installed would be both interference fit & bonded in some manner if satisfactory performance (no creaking bb's) is to be achieved.

I'm imagining in my mind a PF30 to BSA adaptor in the same fashion as the venerable Truvative American to BSA being one potential. It couldn't be aluminum though. Carbon/aluminum really don't play all that well together with out special precautions.

That's a much better response than I'd actually expected. Makes sense, given the heat and pressure needed for a cure.

While I was doing a search for a new gravel bike or frame, I was surprised at the number of aluminum frames that used press fit. That’s just stupid though I’m aware it’s a lot cheaper to manufacture such a frame, but I avoid press fit completely.

Ribble has a bunch of their SL models with BSA BBs.. Their higher end frames with BB72s.

What exactly are the tradeoffs/benefits?

That is good, because if you did purchase on rhymes you wouldn't be able to own an aluminum or a carbon bike because they don't really rhyme.

It is not a reliable system that is why I suggest going to a headset style standard with high tolerances and then also using thread together BBs but I doubt the industry really wants to adopt that to any degree.

Creaking wasn't a problem BITD....but threaded metal sleeves losing their bond with the CF frame was, from time to time. Particularly in the bottom-line and weight obsessed end of manufacturing. Given that threaded BBs universally need high-torque to set them in place or remove them (40Nm thereabouts), at least high torque for bikes, the bond between materials needs to be quite strong

I have a vintage Kestreal Talon from 2002. Threaded BSA metal insert, was still bonded just fine when I retired that rig 10 years ago. Kestrels weren't that light, but they were well made--and back then made in the USA ).

Which is why manufactures came up with the jolly-good idea of press-fitting bearings. It save money on manufacturing trying to get a metal sleeve to fit perfectly in a frame and bonded well...when you can just mold a bearing holder while you're molding everything else.

Headsets don’t creak like BBs because they aren’t under anything like the same stresses as a BB. The bottom bracket is where all the effort of all those hamer-dropping crabon-frame-sploding sprints to the City Limit sign gets turned into forward motion. The headset is just there to point the way.

After 20 years of riding mtb, threaded has been the most durable and silent BB. I think bike manufacturers will go back to threaded BB on all mountain bikes. Roadies have always complained about creaking BBs.

I actually recently have come to believe that thread together BBs in press-fit frames might be the sweet spot.

At least in the face of so many “standards.”

-mr. bill

Hambini might be able to give some colorful input on this subject...

Personal experience, FWIW: I have had one bike with a press fit BB, an aluminum CX bike that started creaking within about a year of new. I have a carbon fiber Ciocc with with a BSA threaded BB bonded to the frame. In roughly 10,000 miles I have had no problems with this setup. Then there are the steel-framed bikes with threaded BBs, a combination that just seems natural.