Originally Posted by
Sy Reene
Perhaps counterintuitively to what's typically offered by metal fab bike makers, TLAB's default and recommendation is a press fit bottom bracket. I assume this is what you have and it's been perfectly fine? I do wonder why they don't offer T47 instead of BSA though.
Yeah, I have BB386 with SRAM DUB on the T-Lab and it has been fine. I also have a BB86 pressfit (Campagnolo) on my steel Breezer Venturi for 8 years, and it has been fine as well.
I guess it’s more typical for metal fabricators to use threaded/BSA, is that what you mean by counterintuitively?” That may be true, but both the T-Lab and the Breezer are uncommonly excellent frames, showcasing design elements most metal frames either ignore or attempt to address in different ways. The Venturi, for example, is built with stiffness paramount, and in addition to an oversized (for steel) and shaped downtube, also uses short, oversized, asymmetric chainstays, both elements requiring BB width beyond BSA spec.
As I understand it, the problems with pressfit (creaking, bearing drag) are really specific to carbon fiber frames, where it’s quite difficult to meet the tolerances required for roundness and alignment due to the nature of common construction methods with the material. Machining metal does not present the same problems, so pressfit is not an issue there.
As for why T-Lab don’t offer T47, I can only guess that there is no benefit to doing so. They’re maxing out BB shell width, in relation to q-factor, with 386, allowing them to do the tube shaping and chainstay widths they want (for stiffness and tire clearance). T47 is an external bearing format, so in order to maintain the q-factor, they’d need to reduce bb shell width, losing real estate for shaped tubes and clearance spacing. I suppose they could engineer around that in some way perhaps, but at what costs and compromises to gain nothing? I’ve not spoken to T-Lab about it, so that’s just my take.