I’d trust a Trek T47. I’ve seen zero reports of a T47 problem on any bike so far. Plus Treks come with a lifetime warranty.
only one recent datapoint, but after buying my bike almost 5 years ago I came to the conclusion it was better to spend less on the bike and more on a few key upgrades. This time around I’m thinking the Bontrager Aeolus Pro 3V wheels and aero cockpit (probably Enve, possibly the Madone if it works with Domane).
This is probably an over simplification, but isn’t T47 an oversized BSA which many have touted to be problem free?
As far as I understand the difference is that BSA was popular in a time when most frames people bought were made of metal. (I have no first-hand experience of BSA BBs on a carbon frame.) On metal this solution makes perfect sense since it is very easy to cut a thread into metal, i. e. you cut the thread directly into the frame. With carbon frames you need to bond a metal piece to the BB, and you put the threads into this metal insert.
It seems to me that you’d still need to do this with a high degree of precision. And you need to precisely bond these two dissimilar material in a durable fashion. This is of course entirely possible, but requires careful manufacturing and good tolerances.
I think the argument of T47 proponents in this thread is that this is overall easier than making the carbon frame itself to spec so that you can press the bearings into the frame directly. That is because the bearings are pressed into a metal cup and you can machine these metal cups more easily with a high degree of precision (e. g. with a lathe). The alignment of the bearings would still require that the metal threads bounded to the carbon on the receiving end are precisely aligned, though.
The price you pay is that this construction is inherently more complicated and introduces more manufacturing steps (which adds cost and potential for manufacturing defects in each of these additional steps). Also, just because you can machine metal parts to high precision doesn’t mean that you necessarily do — you’d also have to ensure that you stick to the required tolerances during manufacture. And if you watch some of Hambini’s videos on SRAM GXP cranks, this does not always seem to be the case (the audible lack of adherence to tolerances is between metal parts).
There are more carbon bikes than you think with BSA. Stevens has done it forever, Specialized has had it the past few years, some or maybe all Bianchi’s have it, Pinarello too.
Side note, I hate when people bring up Hambini and assume that all parts are like the ones he shows. He is getting the worst of the worst stuff that isn’t fixed by normal methods, or don’t work with standard parts, so likely the far outliers. All of this does not excuse manufacturers for not paying for better tolerances.
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I know, but. I don’t have any experience with them. Although I think Pinarello uses a different (threaded) BB standard than BSA, don’t they use the Italian standard?
The only difference is the thread pitch…BSA and Italian BB’s are functionally the same, for all intents and purposes.
You just keep making up these speculations. As other have pointed out, the bicycle industry never stopped making threaded bottom brackets in carbon frames. This is not a forgotten technology. I’ve owned four carbon frames with BSA and have never had a single problem. For example, the lower spec Specialized SL6 has had a threaded BB for years. The only news from Specialized is that they are using this BB on the higher end models of the SL7.
I understand that. Honest question: why didn’t the bike industry return to the BSA standard and instead invented a new threaded standard? (I understand that crankset manufacturers prefer larger axle diameters and you would like to have larger bearings. But in engineering you don’t necessarily need “better”, you need “good enough”.)
Because I think another very legitimate gripe many people (including myself) have with BBs is that there are way too many standards out there, and the Cambric explosion of BB standards started with the move to pressfit BBs and often (understandably) gets associated with pressfit BBs.
I don’t have any inside knowledge as to why they didn’t just go back to BSA BB’s, but based on my experience in the bike biz and product developer, I would say it was primarily market forces.
“Small diameter” BB’s are now viewed as old-tech and “low end”. The consumer believes that a larger diameter BB is stiffer, lighter, better…but also don’t like PF.
And agreed that the multitude of “standards” is a contributing factor.
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But but but… “good enough” doesn’t sell bikes, “better” sells bikes 
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Just to clarify some things:
BSA has too small a diameter to accommodate a 30mm spindle. 30mm spindles, generally speaking, allow for lighter cranksets because the spindle can be made from aluminum… T47 is more attractive crankset-compatibility-wise than BSA, which is probably the reason manufacturers move to it rather than back to BSA.
Furthermore, T47 was designed so that it can be obtained by cutting threads in a (46mm diameter) PF shell assuming it is metal. However given the larger diameter than BSA, it is much harder and more tool-intensive to do especially on ti-frames which is why the higher price. The bb tubes used are otherwise identical.
For a steel frame, you could always relatively easily modify your PF shell into a T47 if you want.
All that being said, I am also queued for a custom steel frame and am not sure what bb I should get…
I went for a T47 so that I could fully route the hydraulic hose internally. A BSA BB wouldn’t have enough spacing and the hose will have to exit on the down tube, wrap over the BB and enter the chainstay. Have a chat with your shortlisted builders and they should be able to advise you better.
Yes, I will discuss it with him, but I still have 8-9 months before reaching the front of the queue…
I am not concerned with any routing considerations, since it will be externally routed mechanical and rim brakes. I guess the decision will come down to what crankset I want to use and what seems more future-proof at the time.