What is a T47?
The T47 as a larger version of traditional, and well-loved BSA threaded BB shells. T47 bottom bracket shells actually start life as standard 46mm inner diameter shells and are then threaded to M47x1.0mm. Much like a BSA shell, the right, or drive side, of the shell is left hand thread, and the left side, or non-drive side, of the shell is right hand thread.
T47 is Adaptable
T47 advantage is it’s adaptability to different crank spindle diameters and frame widths. With larger cups, T47 can accommodate bearings compatible with 30mm spindle cranks, 29mm DUB, 22/24mm GXP and 24mm Shimano crank spindles all while giving you the option of either inboard or outboard bearing configurations. Press-fit systems have evolved over the past few years to include shell inside diameters as small as 37mm. These small diameter press-fit shells are not ideally suited for today’s larger diameter cranks.
T47 is Stiff
The bottom bracket junction comprising the seat tube, down tube and chain stays is a key part of a frame’s stiffness. Bottom bracket shells with smaller inner diameters such as BB86 generally have to resort to wider bottom bracket shells and beefier tubes to achieve what the PF30 (46mm) starting platform can do with smaller diameter tubing. Because a T47 shell starts with a 46mm inside diameter, and has no width restrictions, frame builders have a rather large platform to build up the bottom bracket area of the frame the best way they see fit to achieve their frame’s performance goals.
T47 is used by
While it has taken a few years for T47 to gain acceptance, we have seen a steady increase in small and custom builders choosing to build frames with it. Especially common on many custom titanium and steel frames, there are also a few brands using aluminum T47 shells in carbon frames (Rodeo Labs, Ibis). The most exciting development is that Trek has begun to build frames with T47 shells. The 2020 Domane frames are built around T47 shells, some of them shipping with Wheels Manufacturing BBs installed.
- Shell widths: 68mm, 73mm, 84mm, 86.5mm, 92mm, 100mm, 121mm
- Shell inner diameter (ID): M47x1.0 Threaded
- Individual Cups thread directly into frame
- Drive side = Left Hand threads
- Non-Drive side = Right Hand Threads
- Accepts 24mm and 22/24mm cranks
- Accepts 30mm spindle cranks