You've likely heard the instant ripples coming across the internet; yes, there is another bottom bracket spec coming down the line. This time, however, it is not driven by a big corporation wishing to redevelop a standard to sell more of their branded components, it's origins lie among a small frame builder, a family owned component company, and the man who has been responsible for the explosion in frame building today by developing more high quality fiddly bits and offering them for sale, than any other.
It began one year ago, at the Philly Expo, when a conversation between a customer and a builder blossomed into a discussion on what needed to improve upon the bicycle as we know it. At the crux of the conversation, the inadequacy of most frame builders to accurately create a high tolerance, well machined interface for the press fit 30 bearings, and therefore, the erosion of consumer confidence in the standard.
Once you've been in this industry long enough, you begin to see "trends" come around a time or two. The complaints about the press fit 30 bottom bracket ring through the air; the bearings must be pressed in with a special tool, after use they can creak and make noise, bearings fail more rapidly, they are hard for consumers to work on, etc... Anyone remember Klien, Fat Chance, and a few others? Pressed in bearings that gave people fits and subsequently went back to threaded interfaces...here we go again.
Let me introduce the T47 bottom bracket; a piece that begins with the same inner diameter as the press fit 30 and then adds threads. Isn't this just a bigger standard English bottom bracket? Nope, let me explain why...
The T47 has the following positive attributes:
- uses a larger shell to allow oversized diameter tubing to match without swaging
- the shell is thick enough to allow welding of both steel and titanium without distortion
- the threads are properly sized to facilitate hand tapping post fabrication and for maintenance
- the bb shell will allow cups to fit all current crank spindle sizes
- existing frames with press fit 30 metallic shells can now be reamed and tapped with threads, prolonging their lifespans of use
- at least three bottom bracket manufacturers are already producing parts for this spec, so parts will be available
The T47 has the following negatives characteristics:
- weighs slightly more than a standard English bottom bracket shell of the same width
- builders will have to purchase new taps and make tooling accommodations
- people who like to grumble have another opportunity to do so
I've been fortunate to have known of this for quite some time and I'm in favor of it. I like the fact that if I include it in a build, it allows the customer to have options in the future. I like the fact that it will save some frames already equipped with noisy pf30 shells. I like the fact that a certain headset maker whose product I love will be making their first bottom bracket to match this spec. I like the fact that I have a shell in my hand to build one of the first bikes...off to the shop to start making plans.