From threaded to press fit and back to threaded again?

[Lina]

Hambini is also selling his own BBs that "solve" BB issues. He has his own skin directly in the game when he's telling people press fit BBs are bad.

[Cemicar]

So people think the industry moves to T47, but I rather have the opposite impression. Too many brands still stick to BB86. Most of the cases where a brand moved to a threaded is simply because their previous choices were neither BB86 nor BB386, but worse and more troublesome standards (e.g. BB30, OSBB, BBRight or BB90) so eventually a change was required. I doubt it's a matter of torelance as a youtuber claims, but durablity or maintenability mattered more.

[MagicShite]

Hambini is also selling his own BBs that "solve" BB issues. He has his own skin directly in the game when he's telling people press fit BBs are bad.

I'm a long time watcher of hambini's and I never once interpret his work as him telling people PF bbs are bad. His point is always more of "most manufacturers cheap out on PF BB QC".

He shits more on BSA/threaded BBs than PFs. Him, like many of us others actually prefer PF.

[naylor343]

Hambini is also selling his own BBs that "solve" BB issues. He has his own skin directly in the game when he's telling people press fit BBs are bad.

In defence of Hambini here. I emailed him about a new BB for the bike I was riding at that time, a TCR. He replied with a few questions about any issues I was having with my current set up. There were no issues with alignment etc, so after a few messages he advised me that what I was using could not be improved on and recommended I save my cash and stick with shimano PF86. One very happy non customer.

[wilwil]

Pressfit is lighter and cheaper to manufacture. On paper, the better way to do bottom brackets. Less parts and stiffer (probably more advantages I am forgetting)

Threaded is more forgiving during assembly, easier to replace for bike shops and end users.

In the real world where bicycle frames are predominantly produced in low-wage countries, whether alloy, metal or composite, consistently making good pressfit appears to be too hard. Additionally, a bad reputation for pressfit bikes has been accumulated among bike reviewers and large parts of customers.

Threaded bottom brackets can hide inaccuracies and careless manufacturing better than their pressfit counterparts.

Logical outcome is bike brands going back to threaded bottom brackets, even if it comes with considerable downsides for some bike designs.
An example would be the Specialized Diverge, a modern gravel bike with a massive tyre clearance but an ancient and narrow BSA bottom bracket. The result is a solid carbon chainstay which leaves no option but to route rear derailleur connections externally.

Could the Diverge have been designed with a larger threaded T47 BB?

[CarlosTheJackal]

Just on the "Hambini says they're all out of tolerance" thing, he seems to measure them up and compare them to the bearing OEM's handbook recommendations.

Those recommendations are just starting points for if you don't know what else to do. They are mostly designed for steel/cast iron housings, and usually thick walled ones at that. The exact opposite of a bicycle BB. It's asinine to jump up and down about bicycle BB's not meeting the specs in bearing books.

Isn't carbon stiffer than steel, therefore you would need a tighter tolerance on carbon than steel? or have I gotten that wrong. IDK.

[Nereth]

Well, not that I know of, but I'm always open to a fact check.

So I looked up toray 700 as a quick example, tensile modulus of individual fibres is about 230GPa. Yes, that's more than steel (~200GPa).

But, your actual volume fill ratio of fibre into your finished composite is only going to be 50-70%, so knock a third off that.

And a good number of your fibres aren't going to be running in the hoop direction. No idea how that layup looks for most CF bicycles, but knock another third off at a guess. Now you're at about 43% of original stiffness = <100GPa. Plus BB's have thin walls a lot of the time compared to bearing housings.

A quick sanity check of finished composite mechanical properties indicates that even the above estimate is optimistic: http://www.performance-composites.com/c ... ties_2.asp

Stiffness isn't the only factor by which you choose these fits either. Thermal expansion issues, irregularity of loading direction, how badly you want to remove or leave clearance from your bearing, etc etc. All can make you deviate from the first-pass handbook fits.

[CarlosTheJackal]

Looking at Hambini's tolerances, they don't seem excessive. The same tolerances appear in multiple places eg SRAM technical manual.

https://www.hambini.com/support/install ... stallation

The SKF guidance is tighter than the above.

[C36]

Large OEMs can and should develop their own fits for their own situations, once they have enough experience and reason to do so. This is normal and accepted in industry.

I cut a bit your quoted message but disagree on this part. Bearings science is mega mature and tolerances are there for a reason. No frame manufacturer has 1% of the accumulated knowledge SKF or SNR have, they should not step in the “that should work” territory, they shouldn’t makeup their own std… and when they did (yes Cervelo we look at you) it was a cover my ass type of move, not a “I think this is better”.

Hambini is also selling his own BBs that "solve" BB issues. He has his own skin directly in the game when he's telling people press fit BBs are bad.

I'm a long time watcher of hambini's and I never once interpret his work as him telling people PF bbs are bad. His point is always more of "most manufacturers cheap out on PF BB QC".

He shits more on BSA/threaded BBs than PFs. Him, like many of us others actually prefer PF.

I second that. I told him about my bearing torque measurement and geometrical checks I did and told me straight there is no reason to buy his BB.

[Nereth]

Large OEMs can and should develop their own fits for their own situations, once they have enough experience and reason to do so. This is normal and accepted in industry.

I cut a bit your quoted message but disagree on this part. Bearings science is mega mature and tolerances are there for a reason. No frame manufacturer has 1% of the accumulated knowledge SKF or SNR have, they should not step in the “that should work” territory, they shouldn’t makeup their own std… and when they did (yes Cervelo we look at you) it was a cover my ass type of move, not a “I think this is better”.

So, while you're right that bearing manufacturers have more bearing knowledge than e.g. bike manufacturers, what they don't have is more application knowledge. What they especially don't have, is the right answer for such a specific application, published in their book that they give away for free when you buy more than a hundred bucks of bearings off them.

Ask them what fit to put on a steel shaft through a steel bearing sitting in a steel housing, and they'll be able to take into account everything - Thermal gradient through the bearing and thus all the changes in size, how much clearance reduction they want, how badly they want to prevent fretting vs how badly they want ring creep to slowly change the contact zone on the rings, how much axial movement needs to be accomodated, and on and on.

The moment you say "but by the way my journal is aluminium instead of steel, is going to fret over it's lifetime, and is stiffer on one end than the other due to the crank. My housing material is anisotropic in both stiffness and thermal expansion, and is not symmetrical across both sides of the bearing. what now?"

Well, you're not finding the answer to that in the goddamn bearing fit tables (which don't even have different fits for different clearances or temperatures most of the time!), and while you probably *can* ask the big bearing OEMs to analyse it in full, assuming even *you* have all the data, the reality is, Hambini is *not* comparing his measured fits to the outcomes of those analyses, which, if they take place, will be entirely proprietary, between the bike and the bearing manufacturer.

I hope you have an understanding from the above of where I'm coming from, so I don't have to lean on the anecdotal evidence below, but I'll give the anecdote anyway because it's interesting and relevant, I think;

I'm an engineer at one of the largest (maybe the largest?) customers in the southern hemisphere of one of the biggest 3 bearing manufacturers you would be aware of. The ones with Three Letter Acronym names. Sometimes they can't make enough bearings for us within the months of lead times we give them, and we have to order from their competitors. That's the amount of bearings we push through.

My company fits bearings onto steel journals and into composite housings which we make in house. They are subject to most of the problems listed above that bicycle BBs deal with. With no analysis whatsoever, very early in the companies life, we had already had enough failures from bearings spinning on shafts and bearings falling out of housings, to realise that they had to modify the fits from the book recommendations, to suit our application requirements. Those fits have been tweaked a few times over the years since, but today, we still run completely different fits to what the manufacturer recommends. The manufacturer is aware of this. They are OK with it and think it is reasonable. They still let us use their logos that indicate that we are a partner that is using their authentic bearings, and using them correctly. Even though we don't meet their textbook requirements.

Fun sub-anecdote: Every few years, we get bearings through where THEIR bearings are out of tolerance by a few microns. These guys are not infalliable. No one is. We mess up our fits too (...more often than they mess up theirs, admittedly, but it's really obvious for us when they mess up theirs because of the nature of our product and work).

Long story short, engineers are hired to deviate from set guidelines. Standing in the bleachers yelling about how the guidelines have been deviated from is... silly and naive.

Having said that, if you asked me to find back the videos that I am referring to, I wouldn't be able to and I wouldn't be willing to put the effort into trying. So it's entirely possible I'm putting words into Hambini's mouth. I just remember closing more than one video in disgust, not hearing it out.

[Aeo]

the outcomes of those analyses, which, if they take place, will be entirely proprietary, between the bike and the bearing manufacturer.

I'm going out on a limb and saying that the analyses do not take place.

I am guessing that your company has complete control over the production of and/or rigorously measures whatever object receives the bearings. The bike industry is very far away from this level of sophistication.

Frankly, it is unfair to unleash airospace engineers like Luescher and Hambini on industrially and artisanally produced bikes

[Nereth]

I don't know, bike companies are smart enough to run structural FEA on a composite layup, or a CFD, which to me is a lot more complex. I could do a hand calc in 20 or 30 minutes and extrapolate the default bearing fits to a better one, given the properties of steel versus the properties of a bicycle I had designed. Or I could use a good 3 point mic and figure out in an hour or so whether or not I was achieving the intended interface forces of the default fit. And then I could tweak the fit to get closer.

Like I said, the way my company figured it out was with no analysis at all. We just noticed bearings failing outside of certain boundaries, so we pushed our tolerance limits around to keep us within those boundaries. We have since gotten a bit smarter than that but... the original modified fits that were come up with years ago and before my time, were still better than the default ones.

That's not to say bike manufacturers are infalliable and press fit is fine. It's entirely possible that the fits used are causing failures. But that's not because they don't meet the bearing OEM requirements. It's because they don't meet the machines functional requirements. It's also possible that BB failures are not caused by fits at all.

[wooger]

Just on the "Hambini says they're all out of tolerance" thing, he seems to measure them up and compare them to the bearing OEM's handbook recommendations.

Those recommendations are just starting points for if you don't know what else to do. They are mostly designed for steel/cast iron housings, and usually thick walled ones at that. The exact opposite of a bicycle BB. It's asinine to jump up and down about bicycle BB's not meeting the specs in bearing books.

Large OEMs can and should develop their own fits for their own situations, once they have enough experience and reason to do so. This is normal and accepted in industry.

Admittedly, poor conicity/ovality/etc is usually not good regardless, and I have, at best, only skimmed some of Hambini's videos, so he might go in more depth than what jumped out at me, and have a valid point at the end of the day. But I definitely feel like I've seen him lose his shit over aly or composite, thin walled BB shells that are not within the spec for thick walled steel shells. And I feel like that's misleading.

If they spec a specific bearing, then it should fit, stay in, and not creak.

In 90% of his videos the OEM fitted bearings have problems, creaking or have failed prematurely. Noone is sending their bike to Hambini if there's not a major manufacturing screw up that's left them with a busted bike.

[wooger]

What I don't get is how / why it's easier to manufacture a threaded BB shell to tolerance than it is to make the pressfit BB shell to tolerance. Surely you must start with a perfectly aligned, correct diameter, round cylinder either way? One just has threads cut into it.

I can't say that I ever enjoyed hammering out old pressfit bearings. At least threaded BB's mean you don't have to do this.

How are you removing the bearings from your threaded BB when you service it? They're pressed in just the same.
And you should be using a press in both cases.

[jlok]

What I don't get is how / why it's easier to manufacture a threaded BB shell to tolerance than it is to make the pressfit BB shell to tolerance. Surely you must start with a perfectly aligned, correct diameter, round cylinder either way? One just has threads cut into it.

I can't say that I ever enjoyed hammering out old pressfit bearings. At least threaded BB's mean you don't have to do this.

How are you removing the bearings from your threaded BB when you service it? They're pressed in just the same.
And you should be using a press in both cases.

If cost is proportional to BB precision, then the question is who bear the precision cost, frame mfg or BB mfg? I believe frame with threaded BB is easier to produce and hence less cost. Align and bond a pair of metal blocks with roughly made holes at BB, face them with the thread tool, job done. The bearing seats on the threaded BB cups will need more precision, and hence higher cost. That's what the mfg is after. My wild guess...