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I am currently deciding to buy a bike and I am really stumped at the differences between a "Threaded" & a "Sealed" Bottom Bracket Cartridge. (I have heard of the PressFit type, but not on one of the few bikes I am considering).

Is there a difference in how they perform and the upgrades I can perform on them down the line?

I am buying a mountain bike in particular that I could use for some light trails.

Thank you in advance!

2 Answers 2

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Threaded vs. sealed is not the right distinction to look at.

threaded vs. press fit is about how the bottom bracket is fixed in the frame. Using threads or just pressed-in.

sealed vs. cup and cone or traditional, is whether the bearing is an "industrial" type of sealed bearing where the balls are in a sealed cartridge and you are not supposed to open it, or if it is balls between a cup and a cone you can dismount, replace, grease and so on. The balls in the latter type can be loose or in a cage.

The first distinction is given by the frame. Ether the frame does have threads for threading the bottom bracket or it does not have.There are several types of thread standards (BSA, Italian,...). The second one is more common with the threaded ones.

Most modern bottom brackets use sealed cartridge bearings and older ones are cup and cone. But in wheel hubs, for example, cup and cone bearings are still very popular and not outdated at all.

You can sometimes decide whether you want to buy a sealed-bearing or a cup and cone bottom bracket, because several different models are available. Especially for the most universal square-taper cranksets.

Some people would also call the individual balls from the bearing a "bearing", but I find that confusing.


In general, the press-fit bottom brackets are put on carbon-fibre frames, because than you do not need a metal insert for the threads to be fixed in the frame. But some frames do feature this metal piece and do allow threaded bottom brackets.

Press-fit bottom brackets can have a reputation of causing creaking. That would most often be caused by imprecise alignment of the opposite press-fit holes in the frame, not by the press-fit mounting principle itself.

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    For modern Hollowtech-style cranksets (hollow spindle with 24 or 30mm diameter) you’ll pretty much always have a bottom bracket with sealed cartridge bearings (“industrial bearings”), right?
    – Michael
    Nov 24, 2022 at 17:16
  • @Michael Yes, that's right. Nov 24, 2022 at 17:22
  • Ah ok, I am quite new to this thing. Thank you very much for the distinctions!
    – exoad
    Nov 24, 2022 at 19:08
  • It may be useful to know that essentially, the vast majority of bikes will come with a type of sealed bearing bottom bracket. Entry and mid range level of bikes are frequently spec'd with a "sealed cartridge" which have the spindle (square taper or splined interface) integrated into the unit. "External bearing" BB's, the most modern type, feature cups and sealed bearings that stay outside the frame and a portion is either threaded or press fit into the bike to fix them. The right side of the crankset now has the spindle integrated with it and the left arm is fixed to it.
    – Jeff
    Nov 25, 2022 at 21:09
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Also a third distinction now mentioned in the existing answer: inboard vs outboard bearings.

Traditional bottom bracket standards had a flaw: the bottom bracket threadings leaves too little space for bearings and spindle, so you cannot have both a set of bearings that last long time, and a spindle that won't be damaged dangerously. Bearing damage is a minor annoyance, but spindle damage is more serious, because it can lead to an injury. Traditionally, bearings were adequate but the spindle was too weak (square taper). It was too weak in cup and cone systems, and it's still too weak in square taper cartridge systems.

Shimano experimented later with Octalink to fix various issues in square taper (perceived and real), but it had two serious flaws. One serious flaw was that Shimano got the crank to spindle attachment seriously wrong, not having a press fit, so with Octalink the crank bolts self-loosen even if initially tight. Another serious flaw was that Octalink made spindle to have large diameter and be hollow (lightweight and very durable), but that left so little space to bearings that Octalink bottom brackets have short bearing lifetime.

The solution was found with Hollowtech II. It has outboard bearings, and spindle is integral to the cranks. Because the bearings are no longer inside the bottom bracket shell, they can be large and durable (and because bearings are just bearings and spindle is integral to cranks the bearings are also cheap). At the same time, the spindle can be very large diameter, so very lightweight and very durable and safe against failures.

The only problem with Hollowtech II is that the outboard bearings may not last long amount of time unless the frame has perfect alignment between the left and right bottom bracket shell threads. Frames not designed for Hollowtech II therefore can end up having short bearing lifetime. Not a huge issue, though: Hollowtech II bearings are cheap.

Also, Hollowtech II got the crank to spindle attachment right, and the crank bolts no longer self-loosen.

So if you have a frame designed for outboard bearings, definitely use only outboard systems and not those old obsolete systems that have flaws. If you have a very old frame, or a frame from a cheap bike not having outboard bearings, it may be you won't experience perfect bearing lifetime with outboard bearings, but outboard bearings would still be my recommendation since replacing bearings is easy and cheap.

When shopping for a new bike, please do buy only outboard bearing bikes, since the frame may not be designed for outboard bearings if the bike has an obsolete bottom bracket. The only alternatives are Octalink (do you really want crank bolts self-loosening?) or square taper (do you really want to suffer an injury caused by damaged bottom bracket spindle?)

I don't think that you will find cup and cone bottom brackets anymore. All of them are sealed.

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    Oy. Square taper is a perfectly fine interface. The spindle is not inherently too weak. Octalink should not have the crank bolts self-loosen; that definitely wasn’t my experience on the system. And what does it even mean for a frame to be designed or not designed for Hollowtech II? All systems require the BB shell to be correctly aligned and faced, or else you get creaking and/or poor bearing life. I think the statement that Octalink had shorter bearing life than square taper is the only correct statement in the answer.
    – Weiwen Ng
    Nov 25, 2022 at 13:52
  • Besides, cartridge bottom brackets for square taper and octalink do NOT need perfect alignment between left and right threading. The bottom bracket is one-piece, on the other side there's only a lockring -- very often a very soft plastic lockring that doesn't do much.
    – juhist
    Nov 26, 2022 at 18:52
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    Brandt + interlocutor do express concern that Octalink cranks could loosen in this scenario. They don't say that this happened to them, or that they have heard/seen it happen to others. An expression of concern is not the same as reports of failures.
    – Weiwen Ng
    Nov 26, 2022 at 20:08
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    Unusually, you did at least show evidence of a number of failed square taper spindles, so kudos for that. However, are the flaws that led to these failures inherent to the square taper design itself, or are they just examples of poor execution of the design, or poor material quality, or improper assembly? In several of the photos, there's a groove in the spindle for a circlip, but this acts as a stress riser. That's a failure caused by how the square taper design is executed, but you could just make a square taper spindle without a stress riser!
    – Weiwen Ng
    Nov 26, 2022 at 20:12

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