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The T47 oversized threaded bottom bracket shell design was introduced in 2015 to much fanfare and claims that it would finally provide a truly universal standard that everyone in the industry could support. The handful of years since have seen mere glimmers of that hope — mostly amongst the custom crowd — but now Trek is rumored to be the first major brand to take the plunge. That’s a big, big deal.
I’ve made my disdain for press-fit bottom brackets clear over the years. I don’t necessarily have fundamental issues with the concept, and I’ve ridden countless examples that work quite well. However, it seems that most of those positive experiences have come from smaller-volume builders that can spare the time and energy to ensure it’s done properly. Mass manufactured bikes have been more hit-and-miss, particularly when they’re made of molded carbon fiber. And worse yet, those problematic frames are difficult to properly diagnose, and can result in months of annoying creaks, groans, and curses in the meantime.
And even when press-fit does work properly, there’s still the matter of multiple specialty tools required for service — one of which is often a big hammer — and the fact that the cups themselves get looser every time they’re reinstalled. And plastic ones aren’t really meant to be reused at all.
So yes, press-fit may not be terrible in theory, but overall, it’s bad enough that it’s an outright deal breaker for many.
T47 instead utilizes an oversized threaded format. There are two versions: one with narrower bearing spacing, the other with wider bearing spacing. But those bearing spacings mimic what’s used currently, and the bottom bracket shell’s internal diameter is essentially identical to PF30 and BB386EVO.
In essence, T47 is the same as PF30 and BB386EVO, but with metal threads instead of a smooth, cylindrical bore. In other words, it’s like the English threaded bottom bracket format we all know and love, but with inflated dimensions to better suit modern frame materials and crank spindle diameters, and with the same ease of installation, removal, and maintenance — not to mention a far greater chance of quiet operation.
The only issue, however, is that none of the bigger brands have bought into the idea — seemingly until now.
Trek is apparently taking the plunge
Trek heaped huge piles of praise on its the then-revolutionary BB90 system it launched in 2007. Press-fit was already a thing, but BB90/BB95 eliminated cups altogether by pressing the bearings themselves directly into the frame itself (BB95 is the same as BB90, but with wider bearing spacing to suit mountain bike drivetrains). Trek touted a weight savings of about 40g relative to conventional outboard threaded cups, and with fewer parts, there was supposed to be less chance of creaking relative to other press-fit systems.
But Trek’s system relies on a level of manufacturing precision that doesn’t seem attainable in reality. And unlike with other press-fit systems on the market, there are few aftermarket solutions available. Currently, I know of only two: Enduro Bearings offers oversized bearing cartridges that press into the frame a little tighter (which is useful for oversized, but not misshapen, bearing bores), and Token recently introduced a dedicated thread-together system, but it relies on undersized bearings that introduce other problems.
For bottom bracket-related issues that a shop can’t solve, Trek has little choice but to supply a new frame, or bring the original one back in-house for an expensive, and time-intensive, repair. And regardless of the final outcome, there’s untold damage done in the meantime to Trek’s reputation (if you have a few hours to spare, Google “Trek BB90 creaking”). Plus, there’s also the issue that, even if there are no problems at all, Trek’s BB90/BB95 frames have never allowed for 30mm-diameter crankset spindles, nor do they work with SRAM’s new DUB 28.99mm-diameter formats.
In short, Trek perhaps has more motivation than other brands to figure something out. Trek has already mostly phased BB95 out of its mountain bike line, and CyclingTips now has on good authority that the Wisconsin company will be the first powerhouse brand to incorporate T47 into its lineup.
This sort of move makes an awful lot of sense. T47-equipped Trek frames should be less prone to creaking, the frames themselves shouldn’t require an inordinate amount of re-engineering (the wide-format version of T47 is basically the same width as BB90), and there will no longer be major restrictions in terms of crankset choice.
When everything is taken into consideration, my guess is that switching to T47 will add less than 100g. That’s not exactly nothing in the eyes of diehard weight weenies, but weight isn’t as important in the public’s eye as it used to be, and for any rider who has already dealt with the scourge of a persistently stubborn bottom bracket-related creak, that will be weight very well spent.
Reading the tea leaves
To be clear, I should explicitly state that Trek hasn’t substantiated a switch to T47, so it isn’t certain when this change might occur, or if it’s even happening at all. But when prodded for a comment, Trek didn’t deny it, either.
“We’re currently evaluating T47 as a potential technology for our road bikes,” said Trek road brand manager Anders Ahlberg.
Assuming Trek really is making the move, there’s a good chance it will provide the necessary spark to prod other brands that currently rely on press-fit systems to follow suit.
Fingers crossed, then? Fingers definitely crossed.