So I was reading this article over on bike radar. All of the relevant manufacturers keep quoting BB stiffness as one of the major advantages to press fit BBs. Now perhaps I’m just not good enough though in 20+ odd years of mtbing and cycling in general I can’t think of a single time when I’ve noticed deflection around the BB on any of my bikes. I’d go so far as to say that on 99% of bikes 99% of riders will never notice this as either they’re simply not of a level to detect it or there are other parts they will notice deflection in, which may mask any BB deflection.

The other advantage sited by the majority is that press fit BB’s are lighter. On a typical system what weight advantage in a like for like comparison does a press fit system offer over a comparable threaded BB? I’d hazard a guess that’s it’s significantly less than is being claimed.

Which I guess brings me to what I really wanted to say in the first place. In the article the Scott spokesman is the only that actually admits that press fit BBs make the manufacturing process much easier. As they reduce tolerances required and give more room to join everything together in a crowded part of the bike which makes the design process easier too.

Is it just me or are we the bicycle buying public being sold an inferior standard in order to make it easier for the manufacturers to make the frames?

How did you get to the ‘inferior standard’ bit?

Reducing tolerances is a good thing, surely – it’s more likely that somethign will keep working in less than optimum conditions?

Giving designers greater flexibility means that weight can go down, tube shapes can be modified to give the required stiffness/comfort more easily etc etc?

– you may not notice the deflection, but its there.
– there is a weight advantage but its only a few gram’s (20-30?).
– as for the manufacturing process much easier, well that can only be good can it?

For the most popular press fit designs, notably PF86/92 & Sram’s PF30 the frame manufacturing tolerances are less than those required for threaded BBs.

The standard/s are inferior as:
– They require specialist tools to install and remove. Granted a standard BB does also require some specialist tools though a BB spanner is a lot less expensive than a bearing press and bearing removal tool.
– As a result of the fact the bearings are usually pressed straight in they’re more prone to be over loaded or slightly misaligned which results in shorter bearing life.
– The majority of systems use the bearings pressed directly into CF slieves on CF frames. This means if there are an manufacturing issues it’s not possible to do any re-alignment/modifications post factory e.g. tapping and facing a BB shell. The most obvious example of that is the Lapierre frames that all broke at the BB cause of a tolerance issue with the BBs.
– Factory cartridge bearings that haven’t been specifically manufactured for bike BB use, as used in a number of the systems, don’t have sufficient sealing to keep the elements out leading to reduced bearing life.
– It’s not possible to fit non ISCG chain guides with them.

As i said above I don’t buy into the supposed stiffness advantages for mtbs. Perhaps on higher end road bikes it makes a difference. Where also a lot the negatives in the system are negated to varying extents. There are also some manufacturers that refuse to use the new standards most notably Santa Cruz. They don’t seem to suffer any issues with lack of frame stiffness or design compromises as a result of refusing to use them.

My personal feeling is that initially most of these systems were developed for high end CF road bikes where the marginal weight savings and stiffness gains created by them were considered highly advantageous. In the process though the manufacturers discovered the BBs made designing and making the bikes cheaper and easier. So they started pushing the systems industry wide in the interests of essentially saving money. In the case of the vast majority of mtbers it’s created a large compromise which is being sold as an apparent advantage.

A carbon road or ht mtb frame with the downtube,seat tube and stays all meeting up with the bottom bracket shell close to its full width is noticable. From the very first pedal stroke I find it stiffer. Try it and see.

From some of the old carbon HT’s that come in for repair to the new wider presfits leaving the shop, its an eye opener. This along with tapered headtubes on both mtb and road are two amazing steps forward in frame building.

The frame and tyre deflect so I very much doubt any rider can tell about the BB even jf they can detect it in tests.
They do it because it is cheaper for them in terms of frame manufacture

My carbon roadbike has press fit BB30 on it. Whether it’s the frame design overall, or the BB or the carbon cranks, I don’t know, but it puts any power I’ve got through to the back end like no other bike I’ve ridden.
I suspect it’s a combination of a number of factors TBH. It does tend to need more TLC tho – annual removal and re-greasing

The frame and tyre deflect so I very much doubt any rider can tell about the BB even jf they can detect it in tests.

I doubt it’s the BB itself (of the cranks axle changeing between 24mm and 30mm), but flex arround the BB is certainly noticable between frames. My Swift is far stiffer than my old Sanderson Life, and in turn both are hung out to dry by my old Cannondale F series. None are BB30 or PF, but I assume the difference will be comparable

FWIW I already have a headset press and various extractors so would happily give them a go

While we get sold the advantages of a bigger crank axle, track sprinters continue to put huge power through old-school Dura-Ace cranks.