Originally Posted by
firebird854
Wow, that's an incredibly informative and well put together post, I seriously appreciate it! Regarding Shimano power meters in general, Stages, iiiii precision, etc. I'd want the dual-sided variant and I've been put off to a decent extent by GPLama's blog post:
https://gplama.com/2019/06/29/shiman...-power-meters/
Also, for the compatible options you mentioned, M30, or BB386, do you have any suggestions on what bottom bracket should be purchased for it to work?
That is a fair reason to look elsewhere. I’m just not sure if it’s a big enough deal to consider leaving behind Shimano shifting and standard/reliable bearings. That decision, of course, is yours.
For BB386, if you have deep pockets:
https://www.bbinfinite.com/products/...20970840555579
I’d probably recommend this. It is a one-piece alloy bottom bracket so it will sort of forcefully correct any small defects in your frame and save your bearings a bit. It uses 4030 bearings... which are probably dual row ball bearings? Not sure. Looks custom. $170 for the one piece.
You then have the other solution which is direct fit bearings like:
https://wheelsmfg.com/bottom-bracket...-bearings.html
Trek tried this approach of directly fitting bearings into carbon and many, many people have had issues with misalignment, creaking and wallowing out of the shell. And that’s despite being designed for the task. You NEED loctite if you go this route. You’re also more at the mercy of the shell tolerances. BB86 asks for a sleeve around the bearing so that sleeve deforms to compensate for poorly manufactured frame shells. Also, these dual row bearings will have smaller balls than a standard bearing and thus will be more likely to wear out, especially with contamination.
For M30, unless you get a 2mm reducer for a BB386 bottom bracket, pretty much your only option is praxis:
https://praxiscycles.com/product/m30-bb86-road/
Their solution seems similar to Wheels mfg but it seems that they went with a ground down standard 6806 bearing rather than a dual row bearing - not sure. If that is true, you will get more “crushing” of the bearing because the bearing stiffness is reduced. In order to achieve similar retention force with less stiffness, there needs to be more interference between the bearing and shell - this means the bearing will get squashed a tenth of a mm or so more than it was designed to. Not great for bearing life. Or worse, you’ll have a bearing that moves around and wallows out your shell (see above).
All in all, using a 30mm spindle in a BB86 shell takes you to the dark alleys of bike engineering. All bets are off, really. It will probably work, but you shouldn’t be surprised if you have issues like the ones I’ve described above.