Basing your purchase off a bottom bracket IE: BB86 vs a T47

[tisun]

I used to not paying attention to BB specs while shopping for frames, until I bought a Tantan XC frame which has BB86/92 BB.  Thing is I wanted to used SRAM DUB crankset which has 29mm spindle.  I couldn't find any thread-together BB for that combo.  So I'm using a pressfit BB, which gets loose very easily with high torque pedaling of mtb-ing.  No more BB86/92 for me.

So now I'm looking to replace my Tantan mtb frame, I skip any frame which has BB86.

[Sakizashi]

I am basically fine with every BB spec except for BB86. Not only was it designed by Shimano to restrict crank options, but it also leaves the least room to run hoses for fully internal routing, making it a pain on some frames.

[adam900710]

Great feedback ! When using the BB86  , are you guys using Loctite green retaining compound ?

Yes, with the activator. But if unfortunately the frameset is really screwed then retaining compound may not help.

[RDY]

I'd take BB86, given the number of 24mm axle crankset options that have recently shown up.  T47 is a very problematic standard.

[Serge_K]

T47 allows DUB spindles, that allows for light carbon cranks. Given the reputation (delamination) and cost (high) and weight (high) of Shimano cranksets, a carbon crankset is an excellent way to drop real weight off a build, for a good price (you can find a crankset for c.150$).
I was wondering why we almost stopped seeing 24mm spindles on carbon cranks, seems to be materials science: Shimano uses steel for a reason: aluminium at that diameter is problematic (flexy). The 28.99mm on the other hand lets you use aluminium (or better).
While it is possible to find 165mm cranks w 24mm spindles, you'll find 10 cranksets w a dub spindle for every 24mm spindle.
From that, for future proofing, i'd go with T47. My own BB is BB86 and i wish it were T47 exactly to try 165mm carbon cranks.

[tjebakka]

T47 allows DUB spindles, that allows for light carbon cranks. Given the reputation (delamination) and cost (high) and weight (high) of Shimano cranksets, a carbon crankset is an excellent way to drop real weight off a build, for a good price (you can find a crankset for c.150$).
I was wondering why we almost stopped seeing 24mm spindles on carbon cranks, seems to be materials science: Shimano uses steel for a reason: aluminium at that diameter is problematic (flexy). The 28.99mm on the other hand lets you use aluminium (or better).
While it is possible to find 165mm cranks w 24mm spindles, you'll find 10 cranksets w a dub spindle for every 24mm spindle.
From that, for future proofing, i'd go with T47. My own BB is BB86 and i wish it were T47 exactly to try 165mm carbon cranks.

Rotor uses steel for their Aldhu24 axles and aluminium for their 30mm axles. That said, I started with 30mm axles and PF4230 bottom brackets for my Aldhu-crankset. That caused me to change bottom brackets too often and it has worn out the bottom bracket shell on my Velobuild VB-R-177 frame. I like to do some maintenance from time to time and don't want to worry about wear anymore. Apart from the drivetrain of course. That's why I'm choosing t47 for my next frame. BSA would also be fine but that's just not the standard anymore.

[jonathanf2]

The Chinese carbon cranks are changing the game with titanium 24mm axles which are now coming in at less weight than DUB carbon cranksets. Easier to swap cranksets across different framesets and not worry about axle size. At this point I'm more than fine completely ignoring the DUB standard.

I guess I can see a place for T47 as a more universal mount, but I hate the non-standardized cups and sometimes different thread tooling. Ideally I'd prefer T47 to just settle on external cups with a standard thread size tool. It would just be a bigger threaded BSA bottom bracket in that configuration. The only difference being either 24mm or DUB sizing. That would make life so much easier!

Unfortunately it currently feels like there are a dozen T47 configurations right now! T47 internal cups are just as cumbersome as trying to use a BB86 pressfit thread together BB, with a thin ass wrench that can sometime slip and scratch your BB shell. I f**king hate that s**t!

[Merry]

Serviceability is something that's important to me. I like to be self-sufficient if possible, and the last thing I need is a proprietary interface or some weird part.

It's why I'm on here to build up my own bike. I get to pick and choose how I want my bike built on a budget.

[Sakizashi]

BB86 will die though, pressfit was killed, in part by opinions rather than facts and BB86 is the last one standing.

IRL, at least in North America, SRAM is rapidly gaining on Shimano, and at the high end, shops seem to be doing a lot more custom builds with SRAM, and even for full bikes are selling >50% SRAM. This, IMO, means Dub is likely here to stay.

The 24mm Ti axles seem to work just fine, but they are a niche product and can't defy basic physics. An aluminum alloy 29mm axle will be lighter while maintaining the same stiffness. It's also cheaper.

The combo of Dub staying around + cheaper than 24mm Ti + the hate towards pressfit means BB86 is going to fade away eventually. That doesn't mean T47 will win, though. BSA works fine for Dub as well.

[Serge_K]

fwiw, on installing T47 BBs w narrow lips: . In the comments, some guy also wrote: "You can also use the flat wrench you showed and clamp it to the bb with any headset press (18eur on ali), then back it off slightly whilst uncrewing the bb."

On 24mm titanium spindles: the internet says that's a better material at that diameter than alu, it's not just vibe. But it remains that because a larger diameter tube is exponentially (?) stiffer than a smaller one of the same weight, dub > 24mm. Also, road frames have been getting beefier BB areas (stiffness, aerodynamics, looks...), and so there's more space for a T47 down there.

T47 offers more optionality: if one isn't tied to one groupset / brand, T47 makes it easier to find the "right" crankset.

[Chiyou]

exponentially (?) stiffer

Polynomially, I believe, as in terms of physics, bending and twisting stiffness involves an area/polar moment of inertia, which is based on the tube diameter to the fourth power (d^4). This doesn't invalidate your main point regarding weight, of course (and 'exponentially' sounds more impressive).