The Basics of T47 Bottom Brackets

Oh bottom bracket standards, why can't you be just a little bit less byzantine?  We've probably all found ourselves wishing there were just a few fewer options when it comes to bottom brackets and crank standards at some point because let's face it: they're just plain confusing! 

We wanted to take a look at T47 bottom brackets because while the standard has a lot going for it, it's not super well understood because it has quite a few different options, and on top of that, different manufacturers handle those options in slightly different ways, and on top of that it attempts to bring a whole slew of already confusing standards under its wing (more on that in the Wrap Up section of this post). 

T47?

But first, what is T47? 

The standard was introduced as a solution to the problems that many were encountering in the various press-in standards such as BB30, PF30, BB886, and BB92, to name just a few.  While these standards were great in terms of stiffness because they placed the bearings relatively wide in the frame, more often than not there would be some tolerance issues in the frame, which would eventually result in creaking.  The solution that many brands presented was just to glue the bottom brackets in, but it's hard to actually see that as a real solution. 

All the while, threads were still just hanging around as a simple, proven solution to keeping one part in another part securely, so in 2015, T47 came along to bring the simplicity and security of a threaded bottom bracket to a format that could accommodate the various crank standards that had come along in the years of press-in bottom brackets. 

The name comes from the threads, which are 47 x 1mm, which obviously means that your frame needs to be built with a T47 bottom bracket shell to be compatible with a T47 bottom bracket.  One confusing thing about T47 is that like BSA threaded bottom brackets, T47 bottom bracket shells are available in a wide variety of widths.  To further complicate matters, many T47 configurations allow you to run cranks that were developed for one of the many press-in standards such as BB30 or PF30, but with a threaded bottom bracket.  So that's T47: a standard that tries to make bring some sanity to a confusing mass of other standards.  The question is: can it succeed?

BB CHOICES

Our main T47 options come from Chris King and White Industries, and with those we can cover all of the standard T47 fitment options.  This guide will focus in on those options, so try to keep that in mind as you go along, because there are other bottom brackets out there that blend standards in other ways that will surely confuse this discussion! 

As with the two companies other bottom brackets, each approaches fitment in a different way: Chris King takes the Fit Kit approach, making a total of 4 different bottom brackets that are used in conjunction with 4 different Fit Kits.  White Industries offers a total of 8 different bottom brackets to fit all of the options.  Both approaches work great, and which one you choose should really just come down to which bottom bracket you prefer.

FITMENT

But First of all, how are you supposed to figure out which bottom bracket you need?  There are a couple of different approaches depending on whether you are building a frame up from scratch or are simply replacing an existing unit. 

Let's look at these different instances:

STARTING FROM A FRAME

So you have a frame with a T47 bottom bracket shell.  Now what? 

You'll need to measure your bottom bracket shell width, and determine the type of crankset you have to start.

If you're building up a road bike (using road bike parts), and you have a:

• 68mm shell: you'll need an external-type T47 bottom bracket, UNLESS you have BB30/PF30 cranks, in which case you'll need an internal-type T47 bottom bracket.
• 86.5, 86, or 85.5mm bottom bracket shell: you'll need an internal-type T47 bottom bracket.
• Once you know the type of T47 bottom bracket that you need, you'll just need to make sure you get one that matches the crank spindle diameter of your cranks.

If you're building up a mountain bike (using mountain bike parts), and you have a:

• 68, 73, 100mm bottom bracket shell, you'll need an external-type T47 bottom bracket, UNLESS you have BB30/PF30 cranks, in which case you'll need an internal-type T47 bottom bracket.
• 92, 86.5, 86, or 85.5mm bottom bracket shell, you'll need an internal-type T47 bottom bracket.
• Once you know the type of T47 bottom bracket you need, you'll just need to make sure you get one that matches the crank spindle diameter of your cranks.

REPLACING AN EXISTING BOTTOM BRACKET

As long as you're not replacing the crank arms at the same time, you can just replace it with the same bottom type as you are removing.  So if you're replacing an external-type bottom bracket, the best bet is to replace it with another external-type, and the same goes for internal-type models.  This of course couldchange if you happen to be replacing the crankset at the same time, and you are either moving to or away from BB30/PF30 (this will only be a possibility with a 68 or 73mm shell).

Remember that while Chris King has just two bearing size options (one for 24 and 22/24mm stepped, and another for 28.99 and 30mm spindle sizes), White Industries has one for each of the different spindle sizes, so the two pieces of information you'll need in order to get the right bottom bracket are:

1. Bottom bracket type (internal or external), and 
2. Crank arm spindle diameter (22/24mm stepped, 24mm, 28.99/29mm, or 30mm).

If you are replacing your bottom bracket with one from White Industries, you can simply measure the outside dimension of the old bottom bracket when it's installed on the bike (make sure to have any dust-caps or extra seals installed when you measure it), and compare it to the list below:

• 91/96mm overall width with 68/73mm bottom bracket shell width: you need an external-type White Industries T47 bottom bracket.
• 91/96mm overall width with 86/92mm bottom bracket shell width: you need an internal-type White Industries T47 bottom bracket.
• 68/73mm overall width with 68/73mm bottom bracket shell width: you need an internal type White Industries T47 bottom bracket.

If you are replacing your bottom bracket with one from Chris King, the best way to figure out your bottom bracket and Fit Kit is to check the Fit Kit Instructions because not only will this allow you to verify that you're getting the correct type (internal or external), but it will also tell you what Fit Kit and specific bottom bracket model you need for your crankset.

WRAP UP

To wrap up, we wanted to say that while we've tried to keep this discussion fairly straightforward to give you a clear answer about which T47 bottom bracket from Chris King or White Industries applies to a given situation, there is more to it. 

One question we've gotten about bottom brackets relates to the confusion that comes up around 30mm spindle cranksets.  There are many different type of these cranks, and they can get extremely confusing!  The most important thing to keep in mind is that cranks that are made for BB30 and PF30 standards (both of which would say BB30 or PF30 on the spindle) are different, and require narrower bottom brackets than other 30mm spindle cranksets (like those from Cane Creek and White Industries, neither of which are BB30 cranksets, even though they have 30mm spindles). 

To further complicate this already muddled situation, some companies (like Cane Creek, to name just one) make bottom brackets that allow you to adapt a BB30 frame to one of the more common 30mm spindle cranksets (like Cane Creek's eeWings or White Industries' MR30 cranks).  Seeing that, you might be wondering what bottom bracket you need, and we would encourage you to 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.  If it has another standard, that's another discussion, and it's probably best to contact us to get help selecting your bottom bracket

So with that background on the subject, we hope you now have the information you need to understand what T47 bottom bracket you need!

If you'd like to go ahead and use that knowledge to purchase a bottom bracket you can get Chris King T47 BB here, or a White Industries T47 BB here.

As always, if you have any questions feel free to contact us!