T47 was soluted a problem that of the creaking bottom bracket.
So what is T47?
The T47 standard is essentially a pressfit 30 shell with threads.
The internal diameter of a PressFit 30 bottom bracket shell is 46mm. A T47 shell has an thread diameter of 47mm with 1mm threads mated to a bottom bracket with an outside thread diameter of 46mm with 1mm threads.
Start with the frame
So you have a frame with a T47 bottom bracket housing. What to do?
You need to measure the width of your centrestand housing and determine the type of crankset you have to start with.
If you are assembling a road bike (using road bike parts) and you have
68mm housing: you need an external T47 centre shaft, unless you have BB30/PF30 cranks, in which case you need an internal T47 centre shaft.
86.5, 86 or 85.5 mm housing: you need a built-in T47 centre column.
Once you know what type of T47 centre shaft you need, you just need to make sure you get one that matches the diameter of the crankshaft.
If you are assembling a mountain bike (using mountain bike parts) and you have
68, 73, 100mm five-way housing, you will need an external T47 five-way unless you have BB30/PF30 cranks, in which case you will need an internal T47 centre shaft.
For 92, 86.5, 86 or 85.5 mm five-way housings, you will need an internal T47 centre column.
Once you know the type of T47 centre shaft required, you just need to make sure you get one that matches the crank shaft diameter.
So how do you determine which T47 bottom bracket to use
Start with the crankset to be installed in the bottom bracket
Choose the bearings that work with the spindle (30mm, 29mm, 24mm or 22/24mm).
The crank shown in the photo below has an available spindle length of 69mm.
If you are installing this in a 68mm wide shell, you would then use the Inboard bearing cups (T47-BB-30MM), which have a frame + BB overall width of 68mm.
With any bottom bracket, the wider the bearing stance you have, the more durability you will get out of the bearings. Select BB cups that position the bearings on the spindle as close to the crank arms as possible.
Crank spindles come in a number of different lengths, so taking proper measurements will point you in the right direction.
The most accurate measurement is going to be from the inside face of one crankarm to the inside face of the other with both arms attached to the spindle. This is the usable space on the spindle that the frame plus bottom bracket can fit into.
Seeing that, you might be wondering what bottom bracket you need, and we bring the discussion back to the start of this article: first, what type of bottom bracket shell does you frame have? If it has a T47, then you can simply use the guide in this post to determine what bottom bracket you need.
