In general weight savings are the primary driver of the higher BBs. It would not be reasonable to assume that they are more durable. Iida N, Dzutsev A, Stewart CA et al (2013) Commensal bacteria control cancer response to therapy by modulating the tumor microenvironment. 342(6161):967–970. https://doi.org/10.1126/science.1240527 García-Cayuela T, Korany AM, Bustos I et al (2014) Adhesion abilities of dairy Lactobacillus plantarum strains showing an aggregation phenotype. Food Res Int 57:44–50. https://doi.org/10.1016/j.foodres.2014.01.010

The design comes about as a solution to the well documented creaking issues associated with oversized press-fit systems. While these issues are near always the result of poor tolerances, the T47 standard promises to fix the creaking issue without sacrificing the benefits of an oversized interface. Pros: Lighter weight; more resistant to axle twist; more heel clearance; larger-diameter shell and spindle; potential for narrower pedal stance width Very closely related to Trek’s BB90/BB95 system is the BB86/BB92 standard used by Scott, Giant, Pivot, and many others. If the frame has a press-fit BB shell (without threads, threadless), then you need quite expensive, special tools to install and remove/change BBs. If not using such tools (like a bearing press), bicycle frame can be damaged.I think it’s more about the simplicity of the manufacturing process,” says Drew Guldalian of Pennsylvania-based custom builder Engin Cycles. “Boring out a [standard] BB30 is not impossible, but in my opinion it’s an unrealistic task from a manufacturer’s standpoint that needs to do something to make money. Pan H, Guo R, Ju Y et al (2019) A single bacterium restores the microbiome dysbiosis to protect bones from destruction in a rat model of rheumatoid arthritis. Microbiome 7(1):107. https://doi.org/10.1186/s40168-019-0719-1

Pros: Easy at-home service; interface surfaces can often be machined; huge selection of parts and accessoriesBecause you have aluminium threads and surfaces, you can face the shell with a cutter and make it parallel if it is not. The bearing bores are usually round already, with aluminium cups, because it is a machined surface, and if the bearing bores are too tight you can sand them out and get the fit just right for the bearings before you thread them into the frame. You cannot use a facing or cutting tool that I know of in a carbon shell.” So it’s mostly eyeballing and trial and error. Some very rough guide (what I often try with first) would be: The idea is simple, by moving the bearings outboard of the shell, you can then use a much larger spindle. Currently, 24mm is the accepted norm compared to square-taper’s relatively minuscule 17mm diameter.

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As it stands, this new standard may just become the hot new thing among smaller manufacturers of metal bikes. This system is not without its issues however, with shells becoming oversized (due to wear) being a relatively common problem (leading Trek to release the very slightly oversized V2 bearings to compensate). The 30mm bearing is a good choice when using thinwall aluminium spindles,” he says, “and the narrow bearing stance (relative to outboard bearings) works perfectly with our carbon arm design needing to make the turn into the spindle. The OSBB is basically the same as BB30 but with a little tighter tolerances and a 0.5mm difference in the clip-to-clip dimension. Cranks of both systems are compatible with each other.” In concept, at least, all of the standards we’ve covered are functionally sound. But the realities of relaxing tolerances can create other issues.