{"id":8286,"date":"2020-12-14T03:07:37","date_gmt":"2020-12-14T03:07:37","guid":{"rendered":"https:\/\/www.firstcomponents.com\/?p=8286"},"modified":"2023-05-26T01:40:58","modified_gmt":"2023-05-26T01:40:58","slug":"threaded-bottom-bracket","status":"publish","type":"post","link":"https:\/\/www.firstcomponents.com\/de\/threaded-bottom-bracket\/","title":{"rendered":"The Threaded Bottom Bracket Ultimate User’s Guide"},"content":{"rendered":"\n

A (non-ebike) modern road or mountain bike has either a threaded<\/strong> bottom bracket or press fit<\/strong> bottom bracket\u2014those are the choices.<\/p>\n\n\n\n

Press fit BBs were, arguably, a solution to a non-problem with threaded BBs.<\/p>\n\n\n\n

Consistent dissatisfaction with press fit has seen a return to threaded bottom brackets and the increasing uptake of T47 threaded BB standard by leading brands.<\/p>\n\n\n\n

Read on or click through the Contents<\/em> to access the detailed sections in this unique look at the enduring and dependable threaded bottom bracket.<\/p>\n\n\n\n

CONTENTS<\/strong>
\u2018BSA\u2019 – The original threaded bottom bracket standard<\/a>
T47\u2014The return of the threaded bottom bracket?<\/a>
Threaded Bottom Bracket Preparation <\/a>(esp useful for bike professionals<\/strong>)
Installation<\/a>
Maintenance<\/a><\/p>\n\n\n\n

THE ORIGINAL THREADED BOTTOM BRACKETS – BSA & ITALIAN<\/strong><\/h2>\n\n\n\n

<\/p>\n\n\n\n

Two types of threaded bottom bracket are most commonly used, with the first, BSA, the most widely adopted. Italian threaded come a distant second and have likely already been overtaken by T47.<\/p>\n\n\n\n

BSA<\/strong><\/h3>\n\n\n\n

<\/p>\n\n\n\n

We go into detail about BSA bottom brackets<\/a> elsewhere; but here\u2019s the story in brief.<\/p>\n\n\n\n

\"External<\/figure>\n\n\n\n

Interlocking threaded surfaces is modern engineering\u2019s foundational method for assembling complex wholes out of parts.<\/p>\n\n\n\n

And although bicycle component design is becoming more modular, particularly in e-bikes, threaded surfaces are still the way to bind parts to each other.<\/p>\n\n\n\n

\u2018BSA\u2019 is the common reference to the English<\/em> threaded bottom bracket the production of which came to be dominated by the British company, Birmingham Small Arms.<\/p>\n\n\n\n

Not that bicycle tech purists will tell you to not use \u2018BSA\u2019 to refer to this standard\u2014BSC, or British Standard Cycle, or BS for short, is the correct usage they sternly advise.<\/p>\n\n\n\n

\"cup
Courtesy of the Pedal Pedlar<\/a><\/figcaption><\/figure>\n\n\n\n

The British domination of the standard makes perfect sense as the modern safety bike is a British design invented in the isles from where it took over the world.<\/p>\n\n\n\n

Italian Threaded Bottom Brackets<\/strong><\/h3>\n\n\n\n

<\/p>\n\n\n\n

The Italian standard has existed as a long-standing conventional threaded alternative to the English threaded\u2014a left-hand thread\u2014drive side.<\/p>\n\n\n\n

Older bikes on which Italian threaded can be found include Cinelli. One contemporary brand still using Italian is Colnago.<\/p>\n\n\n\n

The key difference is a right-hand thread on the drive side bearing cup and an outer diameter of 36mm (vs 34.8mm on English-threaded).<\/p>\n\n\n\n

The technical argument against a right hand thread is the problem of precession where crank rotational forces can loosen the cup.<\/p>\n\n\n\n

Even though Italian threaded BBs are rarely used on contemporary bikes, they are still widely available for the brands which do.<\/p>\n\n\n\n

T47 THREADED BOTTOM BRACKET<\/strong><\/h2>\n\n\n\n

<\/p>\n\n\n\n

\"T47<\/figure>\n\n\n\n

Chris King developed the T47 standard<\/a> in 2015 as a solution to a decade of reported issues with press fit BBs, from BB30 through to PF30.<\/p>\n\n\n\n

Now, there are as many cyclists who defend press fit designs as there are those who complain about them.<\/p>\n\n\n\n

Most cyclists have never experienced any issues with press fit and most of those who have don\u2019t care about the creaking when it occurs.<\/p>\n\n\n\n

So the \u2018problem\u2019 does not exist for a sizable portion of cyclists.<\/p>\n\n\n\n

PF30<\/a> reversed BB30\u2019s direct placement of sealed bearings in a 42mm BB shell by re-inserting them into cups which were then pressed into a 46mm shell, expanding the internal diameter by 4mm.<\/p>\n\n\n\n

Creaking bottom brackets continued to be a problem, however, because the real issue was frame manufacturers\u2019 variable BB shell tolerances coupled with variability in bottom bracket bearing cups\u2019 external diameters\u2014a few micrometers can make a hellava difference.<\/p>\n\n\n\n

\"Pf30<\/figure>\n\n\n\n

What, then, if you cut threads into a 46mm BB shell nominally meant for a PF30 BB?<\/p>\n\n\n\n

Firstly, you\u2019ve got room inboard and even outboard which can accommodate the biggest bearings possible, thus extending their life.<\/p>\n\n\n\n

Hambini has built his Youtube career on criticizing the big brands for their lack of attention to frame tolerances.<\/p>\n\n\n\n

He argues the fault is not with press fit as a design, but manufacturers\u2019 sloppiness.<\/p>\n\n\n\n

He has responded by coming up with his own bottom bracket design<\/a>, marrying the most precisely machined alloy bearing containers with the high quality bearings.<\/p>\n\n\n\n

The question is, though, what practical advantage is gained from such high tolerances?<\/strong><\/p>\n\n\n\n

If a BB shell is out of shape, a perfectly machined bottom bracket won\u2019t help.<\/p>\n\n\n\n

Although it\u2019s early days for T47, expect to see increasingly greater adoption the deeper we get into the 2020s.<\/p>\n\n\n\n

THREADED BOTTOM BRACKET PREPARATION<\/strong><\/h2>\n\n\n\n

<\/p>\n\n\n\n

\"Cyclus
Premium Tapping and Facing Tool<\/figcaption><\/figure>\n\n\n\n

In an ideal world you take a new threaded bottom bracket and, with a little grease plus the right wrench, install it into a new bike as an initial assembly, or into an existing bike, without complications.<\/p>\n\n\n\n

The potential problems to be aware of in the real world are<\/strong>:<\/p>\n\n\n\n

    \n
  1. cross-threading a threaded bottom bracket\u2019s cups or BB cartridge into the BB shell<\/li>\n\n\n\n
  2. mutual mis-alignment of external or \u2018outboard\u2019 bearing cups<\/li>\n<\/ol>\n\n\n\n

    Threads and Faces<\/strong><\/h3>\n\n\n\n

    <\/p>\n\n\n\n

    Frame factories usually outsource the cutting of threads into the bottom bracket shell, and 99\/100 times, the threads will be good\u2014you can smoothly install a BB without snags.<\/p>\n\n\n\n

    Tapping the threads, nevertheless, eliminates the 1% of defective threads.<\/p>\n\n\n\n

    You are spared the hassle of wondering why a particular BB unit is so hard to turn in the shell leading to the question: \u201cHave I cross-threaded this?\u201d<\/p>\n\n\n\n

    \"Clean<\/figure>\n\n\n\n

    Clean, and therefore square, faces are also important.<\/p>\n\n\n\n

    In sum, proper threaded bottom bracket preparation means a mandatory session of tapping and facing.<\/p>\n\n\n\n

    (Note also that a BB shell with stripped threads can often be repaired by re-cutting the bottom bracket shell).<\/p>\n\n\n\n

    Threads<\/strong><\/h4>\n\n\n\n

    <\/p>\n\n\n\n

    Faulty threads on BB cups or cartridges are extremely rare due to super-precise manufacturing processes and techniques employed by modern factories.<\/p>\n\n\n\n

    But you may need to prepare for possible imperfections in the bottom bracket shell by following the steps below, or at least understanding the basic how<\/em> and why<\/em> of the process.<\/p>\n\n\n\n

    Because the tool required is prohibitively expensive and takes an experienced hand to work it properly, a bike shop pro is the one to carry out the procedure, unless you have the resources (the tool and the skill) to DIY.<\/p>\n\n\n\n

    At any rate, you\u2019ll find knowing what he does, and how he does it, extremely useful as a bike owner.<\/p>\n\n\n\n

    Faces<\/strong><\/h4>\n\n\n\n

    <\/p>\n\n\n\n

    The bottom bracket shell\u2019s outward facing edge accumulates frame primer and paint overspray when the frame is being painted.<\/p>\n\n\n\n

    Shaving this back to the surface of the alloy or the steel of the BB shell makes the left and right faces parallel to each other.<\/p>\n\n\n\n

    Parallel faces ensure the bearings are square to the frame and the cranks as a result.<\/p>\n\n\n\n

    That means longer bearing life and minimizes the possibility of bearing creak.<\/p>\n\n\n\n

    Bottom Bracket Shell<\/strong><\/h3>\n\n\n\n

    <\/p>\n\n\n\n

    A bike frame\u2019s bottom bracket shell is the smallest tube from the group of tubes (top tube, down tube, head tube, seat tube, seat stays, and chain stays) a frame factory welds into a frame.<\/p>\n\n\n\n

    Frames are constructed in batches or \u201cproductions\u201d. They\u2019re welded, straightened (the deformities are literally hammered out of them in the last instance), and at some stage during the final processing sent out to a specialist who cuts threads into the shell.<\/p>\n\n\n\n

    A finished frame\u2019s paint job also includes the BB shell\u2019s outside edge, adding as much as 2mm or more to the shell\u2019s width on both sides, material which must be removed.<\/p>\n\n\n\n

    Outboard bottom bracket bearing cups can’t sit squarely against the BB shell’s face.<\/p>\n\n\n\n

    Tapping and Facing<\/strong><\/h3>\n\n\n\n

    <\/p>\n\n\n\n