Why would you want press fit? What's the upside over threaded?

Press fit squeak............ ;)

it seems like they are maybe cheaper to build? For the most part they don't work better than a regular BSA, unless I'm missing something. The BB30 was a leaky mess on my cyclocross bike, I have gone all the way back to octalink and find it works well in a muddy environment.

Well, headsets are press fit. I suppose, new style is integrated. Come to think of it, I would rather have an integrated BB, where the cups are built into the frame and you just swap bearings. Regardless, I think GXP and Shimano outboard bearing cups work perfectly and BB30 that was designed by Cannondale as an open platform for anyone to use is plenty of choices. Shimano and Trek making essentially BB30 in a little twist of difference just to make everything complicated have gained nothing.

True, but they have a nice adjustable bearing preload system. So the cups don't have to be super tight, and they're a piece of cake to service. The pressfit bottoms brackets tend to have either no adjustable preload, or crappy adjustment.

I'd rather see a better pressfit design for carbon - bonding in metal parts is just another failure point.
A thread together BB with something like a 46 ID, 80mm width so the cups on both sides have some depth in the teeth.
That way frame manufacture is simple, BB replacement is easy, one less failure point for the frame.

OTOH I figure that the shell on a metal frame should be machined post weld anyway so may as well put threads in and have a 47mm ID version of the above so there is some consistency.

A lot of bad BB designs and slack mechanics have got us to the point of widespread belief that PF is flawed. Thread together BBs are a lot more foolproof.

Those bearings are pressed into the thread fit components before being threaded onto the frame though, no? (I’m sure this was the PF logic to begin with). So as long as you have proper tolerances and alignment, which should be much easier in an aluminum/steel frame, wouldn’t it be cheaper/stiffer/lighter to go PF?

Actually, no. The bearings fitted to threaded bottom brackets are fitted by heating the housing to a high temperature (so that it expands), sometimes chilling the bearing (so that it shrinks), then pressing them together. Once the respective pieces return to the same temperature (and their original sizes), the fit is much, much tighter than a press fit alone. It won't come loose the way a press fit into a frame does. And, if your frame press fit were that tight, you could never service the bottom bracket at all.

That's why threaded bottom brackets are preferred by everyone but the bike manufacturers. Press fit and their frames are much cheaper to manufacture -- and saving $5 per bike over 100,000 bikes becomes serious money. But threaded are infinitely easier to service and replace by home mechanics -- and much more reliable.

Disposable bearing assemblies don't need the bearings to be removable and replaceable, which helps tremendously in avoiding creaking or whatever.


I don't know, is it really? There's a long history of manufacturers being cheap with finishing work on metal BB shells. There's hardly a good reason that a bike shop should need to use facing and chasing tools on a new frame, yet that used to be common.

Ah that makes sense

I just got a carbon frame with an aluminum sleeve in the BB shell for BB86.

Thread hijack - grease or no grease (BB is Ultegra with the plastic cups) and if grease, what kind?

I think the main push to go to press fit came approx was when the majority of high end frames were starting to become "one-piece" carbon composite. And getting high strength threads molded or cut into carbon fiber composite is either impossible or very very difficult or very expensive or some combination of those. This meant that creating a threaded BB shell on a carbon frame would typically require the precision bonding of an additional part (usually an AL alloy threaded sleeve) into the carbon BB shell. As a result, press fit BB shells were far less expensive and far simpler to manufacture on a carbon frame, in spite of the many issues with the actual BB bearings long term reliability and alignment.

I don't think that there was ever any advantage to press fit BBs on metal frames, except for the fact that press fit was becoming over time the defacto "standard" of new bikes, and that a press fit BB also saved a metal frame manufacturer a few bucks too, seeing as they did not have to make a threaded BB shell.

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Not to mention the huge difference in the loads supported by bottom bracket bearings compared to headset bearings.

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Another big part of why headset and BB bearing assemblies have historically looked different is that a crank spindle is a lot different from a fork. The old threading standards like BSA were designed as part of an adjustable cup-and-cone assembly.

The bits and pieces:



On the right we've got the fixed cup. We just pack it with grease and bearing balls, and screw it all the way into the shell on the drive side.



Next, we've got the spindle. The two bearing cones are part of the spindle itself. We stick it into the shell from the non-drive side, and now the drive-side cone is contacting the bearing balls that we packed into the fixed cup.



Next, we've got the adjustable cup. Like the fixed cup, we pack it with grease and bearing balls, and start screwing it into the non-drive side of the shell. As it gets most of the way in, the cone on the non-drive side of the spindle comes into contact with the bearing balls within the adjustable cup, and the bearing comes together.



Now, we just need to adjust the bearing. We screw the adjustable cup far enough in that spindle won't have play, but far enough out that the bearing will have almost no resistance.

To lock the adjustment in place, we thread the lockring onto the outer threading of the adjustable cup, all the way until it contacts the shell.



So, what's the point?

A practical solid steel crank spindle has a low enough outer diameter that, even if you add cones to it, it can fit within the bottom bracket shell. And it can do that even if the bottom bracket shell isn't made with a huge diameter, which is important because steel isn't a convenient material for making high-diameter tubes: huge-diameter steel tubes need to be heavy to avoid issues like dent vulnerability.

But what about a headset? In a headset, the steering tube takes the role of the spindle.



At that time, nearly all bicycles used threaded headsets with quill stems.

The quill of the quill stem sits inside of the steering tube (and expands against it to stay in place), so the inside of the steering tube needs to be as wide as the stem. And we don't want to force our stems to be super-narrow, because that would make them flexy and weak. Most commonly, this meant that the outside of the steerer was 1". Since the steering tube is inside of the head tube, the head tube needed to be even larger. But because we're talking about vintage steel, we don't want it to be that much bigger, as the 1" diameter of the steering tube is already considerable.

So, what happens if we try to do the headset bearing BB-style? If we added cones to the outside of the steering tube, it would dramatically widen its diameter, and now the head tube needs to be huge.
So it was much better to use external races at the top and bottom of the headtube, where they're not trying to fit between the outside of the steerer and the inside of the headtube.

With the external-race system, the race on the top of the headtube needs to sit "inboard" of the top race on the steering tube. So unlike the bottom bracket where the threaded cups trap the spindle from both sides of the shell, we don't have a way of using threading on the headtube to adjust the headset bearing and lock it in place.

Nothing to add, this is an extremely interesting thread.

Maurice

Not sure if you saw this article?

https://road.cc/...ed-and-bowman-cycles

The irony is while everyone was going press-fit Pinarello never wavered from threaded. Many people talked down their frames for not adopting the new technology and here we are going back.

I started with the cup-and-cone bottom brackets, which were the only ones I think in the eighties. Advantage was you could work on them at home, but they were rather difficult to adjust and especially with three chainrings, you had to replace them rather often.

A big improvement were the "integrated" bearings, where you just had to screw in one piece into the frame. This one piece comprised the bearings, the spindle and the thread. No need to adjust anything, dead-easy.

Than came unfortunately the PF bearings. I have them myself on my P5.
There might be reasons for it (carbon frames, stiffness, lightness), but they are a pain for the home-tinkerer.
I had huge problems to press in the rotor bearings 5 years ago. I used locktite 641 (which was an error, but it was advised by Rotor), and it was (probably due to poor tolerances) extremely difficult to press it in. I feared for my frame. It also did not turn nicely, after a push the cranks only turned half a circumference freely. But I let it on and tried to not think about the BB for years.

A couple of weeks ago water had entered the bearings such that rost had ruined them and I had to replace. Big problems to hammer them out and enter new bearings again. (C-Bear now, someone alledged they are better than Rotor). The cranks turn a bit better now (fifteen circumferences without the chain after a push with the hand)

Probably the most important thing with my next bike is that the BB is not PF, and I'm happy that the situation seems to go in that direction again.

Obligatory YMMV disclaimer

I do my own work, for better or worse. I personally have all BB30 bikes and use a ceramic speed Shimano conversion on all of them. Most have no issues but a few have developed creaks over the years. I find specialized to be really dialed in the tolerances. I have had more issues with Felt and Cannondale. BB30 to work correctly is super sensitive to the bearings used, press method, and preload from your spacers. I think the system is fine but each bike can be picky with setup. In general my best system was 609 loctite, wheel manufacturing angular contact bb30 bearings, carefully pressing in bearings exactly square, and proper spacing with crank. Typically zero issues in all Specialized bikes.

There is an important distinction to make between true press-fit systems like PF-30 and BB-30/BB-90 systems. True press fit systems force the bearings plus outer bearing holders into the frame. This system is cheap to make and allows for a relatively large tolerances so it is a no-brainer for cheap carbon bikes. However by adding the bearing holders you lose many of the theoretical advantage such a system might have over threaded bottom brackets. BB-30/BB-90 systems ditch the outer bearing holders and in doing so require much lower tolerances which costs money. So while the BB-30 system has potential performance advantages they don't have the cost benefits of the PF system. (Technically BB-30 came first and PF-30 was a way for smaller companies to imitate the system but at a much lower cost. The bearing holders act as a bodge of sorts to allows for higher tolerance levels).

For Trek and Specialised the cost difference between their older systems and newer threaded systems (like the T47) make it worth the move if that's what consumers want on higher end bikes. I suspect we may see an expansion of the cheaper PF-30 system on entry level bikes though as a means of keeping costs down. This allows the same cranks etc to be used across a range but lowers but helps reduce the production costs of the entry bikes.

As someone else noted Pinarello has always stuck with threaded BB but I suspect that's because they couldn't meet the tolerance requirements of a BB-30/BB-90 system. To my knowledge Pinarello has stuck to Italian threaded BBs which speaks of stubborn tradition given everyone else uses BSA threads due to their superior design.

https://www.bicyclepartsdirect.com/bb30-vs-pf30/

I noticed that the 2019 Felt IA series have an FSA Mega Exo bottom bracket.

Does that mean they've gone back to threaded?

Edit:
I see on the 2020 IA advanced it says Shimano Hollowtech BSA threaded

The MegaExo is a threaded BB designed for 24mm cranks like Shimano. Manufacturers spec over the Shimano BBs because they are dirt cheap but my experience is you get what you pay for. The good news is when they fail after < 1 year you can put in a standard Shimano BB which will last a lot longer.

Thanks, I know what a mega exo is but what I didn't know is if they were putting an insert into a BB30, putting a bearing reducer in a BB30 or if they were actually making the frame accept a threaded BB.

Ok, I'm completely illiterate when it comes to BB's. I feel like I'm a decent mechanic for my own bikes but BB's baffle me for some reason. I have a 2019 IA10 (regretting not going for the IA3 for a few extra hundred $$ but that's another topic), which came with A Vision Trimax crank and MegaExo BB. From what I understand, that's a 24mm diameter spindle inserted into the MegaExo BB, correct? And The MegaExo BB reduces from a 30mm BB shell down to 24, correct?

I'm in the market for a 165mm crankset, and would either have to find a crankset compatible with MegaExo BB (can't seem to find many, or see above comment about BB illiteracy), or get another crank brand compatible with a BB30 bottom bracket and have a different BB30 bottom bracket installed?

Any suggestions on common BB/crankset combinations used on Felt IA's?

While you can spend a lot of money on nice bottom brackets, you can also get them for quite cheap when they're basic and use adapters. I'd recommend finding a crank you like at a price you like first, then figure out the specific bottom bracket after that. With bb30 you can adapt to pretty much every standard so you'll be okay.

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"...everyone else uses BSA threads due to their superior design."

It depends what you mean by "superior". The single, giant advantage of Italian threading is that the bottom bracket can be/is tapped in one operation for it's entire length, ensuring perfect alignment of the threads, and therefore the cups if the shell is faced correctly. If you talk to a legacy bottom bracket manufacturer (or anyone who has worked/works in a high-end frame shop) you can probably get a list of the prestigious frame manufacturers that have never really been able to hit great tolerance levels in this regard with english threaded BBS.
The downside to the Italian style - precession - is always going to be present, but in practice one can at least make an argument for this being far less present - and pressing - an issue than the alignment issues posed by ENG/BSA BBs.

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