Trek confirms use of T47 threaded bottom brackets — but with a twist

Trek today announced updates for its Crockett aluminum cyclocross bikes. Two builds will be offered — the Crocket 4, with SRAM Apex 1 for US$1,500 / £1,300 / €1,550, and the Crockett 5, with SRAM Rival 1 for US$2,300 / AU$2,800 / £1,750 / €2,050 — both of which will include Trek’s Invisible Weld Technology for visually seamless joints, clearance for 38mm-wide tires, hidden fender mounts, front and rear flat-mount disc brakes and thru-axles, and Bontrager Affinity TLR tubeless aluminum clincher wheelsets.

Geometry is carried over from previous Crockett models, as are the full-carbon forks that are also shared with the carbon fiber Boone. There’s also a bare frameset available for US$1,070, and all of the new Crocketts are available from dealers now, with varying international availability depending on region.

But what is absolutely brand-new — and a groundbreaking moment for Trek — is the inclusion of T47 threaded and oversized bottom bracket shells, just as we predicted a few weeks ago. However, it’s not the same T47 system that is already in use by a number of custom builders. It’s not wholly incompatible at all, but it’s not exactly identical, either.

The same, but different

The current wide-format, internal-bearing version of T47 uses 47x1mm threads and an 86.5mm-wide shell, with the latter dimension chosen because it’s the same as what’s currently found on the PF86 system. However, PF86 was designed from the outset to be a press-fit system, and those cups only have a paper-thin flange to keep the cups from being inserted too deep in the shell.

T47, on the other hand, requires splines on the flanges so there’s something for tools to grab hold of, and although that whisper-thin lip of aluminum hasn’t stopped the likes of Chris King, White Industries, and others from moving forward with T47 as-is, it’s not enough material to facilitate mass assembly at the OEM level.

As a result, Trek has partnered with Praxis Cycles to use 85.5mm-wide shells, which provide an extra 0.5mm of flange thickness. The threading is otherwise the same, as is the actual bearing spacing. And while this is only found on the new Crockett for now, it seems safe to assume that Trek will stick with this modified 85.5mm-wide T47 format for every other T47-equipped Trek frame to follow from here.

“We use a slightly narrower BB shell to get more tool purchase,” said Trek road brand manager Anders Ahlberg. “The standard T47 tool engagement is pretty tight for a larger production environment.”

Ahlberg is insistent that Trek’s modified T47 system does not constitute yet another new “standard”, despite the 1mm-narrower shell. Current wide-format, internal-bearing T47 will also work on the new Crockettt, and according to Ahlberg, both Shimano and SRAM have also stated that their cranks will accommodate either existing T47 cups or these modified ones from Praxis; there’s more than enough leeway in the threaded preload collars that SRAM uses, and enough spline length in Shimano’s Hollowtech II spindle.

That said, it’s important to remember that the inverse is not true; T47 cups that are designed with 85.5mm-wide shells will not work on frames that have 86.5mm-wide T47 shells.

Threaded shells, but lighter bikes

Adding threads to an aluminum frame like the Crockett shouldn’t add up to any appreciable weight gain relative to the previous press-fit version, and in fact, the new Crockett’s 1,325g claimed frame weight for a 56cm frame is about 200g lighter than the previous version (largely owing to the simpler, non-sliding dropouts).

That doesn’t necessarily hold true for a carbon frame, however, which would require additional aluminum inserts to hold the threads since carbon fiber itself can’t be threaded. But while switching to T47 in a carbon frame might add a few grams to the frame itself, it’s important to note that complete bikes can potentially be lighter.

SRAM’s oversized DUB crank-and-bottom bracket system, for example, is lighter than the equivalent GXP system since the former uses aluminum spindles instead of steel ones. That will also hold true for most other companies that offer both 24mm and 30mm-diameter crankset spindles, such as Rotor and FSA. Neither Shimano nor Campagnolo produce anything with 30mm-diameter spindles, though, so switching to T47 on either of those companies’ cranks will likely tack on a few grams.

Still a big step in the right direction

Weight gain or not, Trek’s shift to T47 is still very good news, and for a variety of reasons, including a reduced chance of creaking, easier service, and better crankset compatibility.

As for whether T47 will continue to work its way into the rest of the Trek lineup, Anders wouldn’t commit, but it sure seems like the writing is on the wall here.

“We’re evaluating T47 across our entire model range,” he said. “It’d be a big shift. We’ll do what makes sense for future development.”

www.trekbikes.com