Last year at NAHBS, a new bottom bracket standard was introduced. Dubbed T47, the parameters were set through a collaboration between White Industries and custom bike builder Argonaut Bicycles. Chris King was working on a similar project for a while, but in the end everybody decided to play nice and release one standard, not two.
T47 uses the frame dimensions of PressFit 30: a 68mm wide bottom bracket shell for road bikes and 73mm wide for mountain bikes. The inner diameter of the shell is 46mm. The big change is that the shell is actually threaded, like in the old days
T47 combines the benefits of a large bottom bracket shell, a larger area for the down tube and seat stays to grab onto, with the threads that many riders prefer over a pressed system. From a frame builders perspective this makes a lot of sense. The classic threaded bottom bracket shells have been developed in the days where bikes were made of steel. Steel typically uses skinny tubes.
- A classic threaded frame shows that a lot of things are happening in the bottom bracket area, even with the skinny steel tubes used.
With metal frames using larger titanium tubes and especially aluminum, frame designers had to taper the down tubes a lot to fit on the skinny BSA bottom bracket shells. A larger shell leaves room for bigger chain stays too, so in the end the result is a stiffer bike.
Another benefit of T47 is that it easily leaves room for 30mm crank spindles. In theory these cranks can be made to fit on a classic threaded shell too, but it is tight. Very tight. We are currently working on a redesign of our BSA-30 bottom brackets and we had to jump through quite a few hoops to make things fit.
- A T47 bottom bracket shell provides a lot more surface area for the chain stays, down tube and seat tube to grab onto. This is particularly helpful for oversized aluminum tubes. Photo courtesy of www.bikerumor.com
Like almost any product, T47 faces a few problems too. One of the main drawbacks of carbon is that it is close to impossible to cut threads in it. Therefore the standard is only for metal frames. One could build an aluminum insert in a carbon frame, but that would require bonding this insert in the frame. This adds weight and cost, two things most cyclists are not big fans of. Also, if these aluminum shells decide to break their bonds with the frame, we are back to creaking, the number one problem T47 promised to fix. This time it’s a warranty case instead of a simple bottom bracket reinstallation.
When the new standard came to the scene, it was said that it could be retrofitted on existing bikes with a PressFit 30 shell. So far I have not seen a single successful execution of that. From my talks with people that know their way around thread cutting, it is definitely not something that could be done at a bike shop with hand tools. We have to write off this story as wishful thinking.
So far, not one major frame manufacturer has adopted the T47 standard. This might have something to do with the big guys (Specialized, Cannondale, Trek and Giant to name a few), being too much invested in the tooling for their current standard. It might have something to do with the major brands not wanting to add $20 to their frame cost to start bonding and threading the new standard. In any case, T47 is a major player at the Handmade Bike Show, but I would be surprised if more than 2000 frames were made in 2016.
On the component side, there are several major players offering the bottom brackets: Enduro, White Industries and Chris King all have production available. Praxis has teased it on their Facebook, but does not show it on their current web site.
But what about Kogel T47?
One of our marketing slogans is ‘Any crank, Any frame, No adapters’, so it is not surprising we have received a few hopeful questions from customers. Given the lukewarm response from the frame makers and the intense competition on the components side, we have decided to sit this one out. Between White, King, Enduro and Praxis, there probably is not a bad option on the market. I’m sure if you need a bottom bracket to fit your new titanium wonder bike, you will find a product of your liking with any of these quality brands.