Ever get confused by all the bottom bracket “standards” out there? English thread vs. Italian thread. BB30, BB86 and BB90?

No worries. Here’s your primer on all things bottom bracket, from it’s history and humble beginnings all the way up to today’s emerging technology. It’s everything you need to know about bottom brackets…

The Basics:

The bottom bracket is a critical component to every drive train. Connecting the left and right cranks, this is one of those important elements on the bike that directly effects power transfer between the rider’s legs and the bike’s drivetrain.

While its concept is simple enough to understand, when it comes to bottom bracket technology, it’s easy to get confused. Incremental changes almost every year coupled with a slew of proprietary technologies from major component companies have flooded the market with more options than ever before, and it can be very confusing for the average cyclist. We broke down every type of bottom bracket you are likely to encounter and present them in a simple, easy to understand format. From mountain to road, threaded to pressed, and integrated to external, it’s all here…

Why The Variety?

Bottom bracket compatibility is one of the most confusing topics for amateur and seasoned cyclists alike. Years ago, it was simple. There was one bottom bracket design, and it was strong, durable, and easy to service. Commonly referred to as “one-piece” Ashtabula cranks, these are made of one solid metal piece, meaning the left crank, the axle, and the right crank are all one piece, held in place by cups pressed into the bottom bracket shell. If you still have an older bike or even a newer children’s or department store bike, chances are you will be able to find one of these on there.

Durable and simple as they may be, these cranks are heavy and inefficient. Component manufacturers found that they could shave significant weight and improve stiffness by manufacturing parts from lighter materials, but in order to maintain the integrity of the set ups they would have to change the way bottom brackets were assembled. The innovation race took off in the cycling industry, but companies failed to agree upon a standard development platform, and rapid development quickly made new technologies obsolete.

Loose Bearing Bottom Brackets

loose-bearing-bottom-bracketBefore the 1990’s, loose bearing bottom brackets were the standard on almost any bike purchased outside a department store, and still are for some lower to mid-range bikes. The system consists of a solid metal spindle or axle, with loose, individual bearings that must be packed into retainer rings during installation or after cleaning/inspecting. With this design came the birth of the “square taper bottom bracket,” which gets its name because of the squared ends of the spindle, over which the crank arms are pressed, secured by a bolt. We will talk about other types of bottom bracket-crank arm interfaces later in the article.

The Birth of the Cartridge


A Shimano square taper bottom bracket with cartridge bearings at left.

A Shimano square taper bottom bracket with cartridge bearings at left.


Recently, the loose-bearing system is largely being phased out in favor of another system, known as the cartridge bottom bracket. Much less complicated and with a significantly longer lifespan, cartridge bottom brackets basically encase the mechanical workings of the loose bearing bottom bracket into a much simpler, two piece system. A cartridge bottom bracket consists of the cartridge (duh), which screws (or is sometimes pressed, more on that later) into the drive side of the bottom bracket shell and contains the bearings and spindle, and a lockring, which supports the bottom bracket on the non-drive side.

Cartridge bearings contain all the bearings for each side of the bottom bracket in one unit.

Cartridge bearings contain all the bearings for each side of the bottom bracket in one unit.

This type of bearing assembly is largely the standard for today’s bikes, although there are changes on the horizon, namely in the ultra high-end markets. With a simplified design, overhauls no longer involve tedious inspections of individual bearings, and riders can instead easily and cheaply replace or upgrade the cartridges which hold the bearings.

Threadings and Sizes


The bottom bracket shell is the part of the frame which houses the bottom bracket, to connect the cranks, and comes in a variety of threadings and sizes.

The bottom bracket shell is the part of the frame which houses the bottom bracket, to connect the cranks, and comes in a variety of threadings and sizes.


While a cartridge bottom bracket may seem straightforward, bottom brackets are not one-size fits all. In order for a standard cartridge bottom bracket to be installed on a frame, the two pieces must be threaded into the bottom bracket shell of the frame. This is where choosing a threaded bottom bracket starts to get tricky, because different frames from different manufacturers have different bottom bracket shell sizes, thread sizes and TPIs (threads per inch.) Most frame manufacturers stick to a few more common threadings, such as British, Italian, French, and Swiss, each of which has their own threading and sizing specs. A majority of frames use English threading (1.37″ X 24 TPI) but Italian branded frames (Colnago, Pinarello, etc.) use a slightly different Italian threading pattern (36mm X 24TPI.) French threading is measured at 35mm X 25.4 TPI. The widths of bottom bracket shells also differ; a 68mm shell width is standard for British and French road frames, and 73mm is standard for British and French mountain frames. Italian frames use a unique 70mm wide bottom bracket shell. In order for a bottom bracket to screw into a frame’s shell, its threading must match perfectly with the shell, so check the threading of your frame before ordering a new bottom bracket. You local bike shop will be able to tell you what type of threading and bottom bracket shell diameter your frame has if you don’t know.



Notice the square interface at the center of these FSA cranks.

Notice the square interface at the center of these FSA cranks.


Once the bottom bracket is installed, it’s time to attach the cranks. There are several different interfaces, and crankset interfaces must be the exact same as the bottom bracket to attach properly. The square taper spindle was the original interface, where cranks have a square hole and are slid onto the squared ends of the spindle which get thicker as you get closer to the center. Bolts then press the arms further onto the spindle.



This Miche Primato bottom bracket uses the smaller ISO square taper.

This Miche Primato bottom bracket uses the smaller ISO square taper.


European and Asian manufacturers split when developing their own square taper interfaces, resulting in two standards that survived in the international cycling community. Europe gave birth to the ISO square taper bottom bracket, and Japan developed the JIS, or Japanese Industrial Standard. The two interfaces are remarkably close in dimensions, but the ISO design tapers down to a slightly smaller end. Logically enough, most European brands (Campagnolo, etc) adapted the ISO interface and Asian brands (Shimano, Sugino, etc) stuck with the JIS interface. One interesting note; the Japanese NJS parts highly prized by the fixed gear crowd and used for elite Keirin track races use a European ISO interface, and the parts are threaded to European standards. NJS standards use the same threading as Campagnolo track parts.

Moving Past the Square Taper


From left, a traditional square taper, Shimano Octalink V1, Shimano Octalink V2, and ISIS bottom bracket interfaces.

From left, a traditional square taper, Shimano Octalink V1, Shimano Octalink V2, and ISIS bottom bracket interfaces.


This was just the beginning of the confusion, because manufacturers eventually began to abandon the square taper interface all together, and proprietary interfaces began to surface from some major component companies as the innovation and marketing bugs began to spread. First onto the market was Shimano with their Octalink Interface. Shimano developed a system which would attach the cranks via a splined interface, with eight grooved splines that would line up with eight inverse splines on the crank, replacing the square taper interface.

The Octalink system had several advantages; it created a stiffer interface, giving the rider more power transfer from their legs into the mechanical system of the bike, much more than a square taper bottom bracket. While Shimano did have a major improvement in bottom bracket technology, they quickly patented it, and charged a licensing fee to any company wishing to use the technology in their products, making it inaccessible and expensive to their competitors and other component manufacturers. Keep in mind that cranksets must be manufactured with an interface to match the bottom bracket, so crankset manufacturers had to pay Shimano if they wanted to make Octalink-compatible cranks.

Some companies jumped on board and paid, while others decided to counter Shimano’s stronghold with the development of an alternative to the Octalink system which could be widely used across the industry as an open development standard, meaning any company would be free to develop products using the technology, thus creating an internationally accepted and accessible standard. So major industry brands King Cycle Group, Truvativ, and Race Face got together to develop the International Splined Interface Standard or ISIS, a system which was similar to Shimano’s but used ten splines instead of the Octalink’s eight. Both interfaces are still widely in use today, but ISIS is generally more popular, because it is more accessible.

Outward Bound


External bottom brackets house the bearings inside of cups outside the bottom bracket shell. Bearings are inside the silver rings between the cranks and the bottom bracket shell in this picture.

External bottom brackets house the bearings inside of cups outside the bottom bracket shell. Bearings are inside the silver rings between the cranks and the bottom bracket shell in this picture.


By this time, the race was on to develop stiffer, lighter bottom bracket and crank systems. The focus moved away from development of the interface and began to shift toward structurally superior configurations. As innovation continued, engineers soon found they were limited by the diameter of the bottom bracket shell. To improve power, manufacturers were looking to beef up the diameter of their bottom bracket spindles (axles), but in order to do so, the bearing sizes had to be smaller in order to fit the entire configuration inside a standard bottom bracket shell.

Smaller bearings mean less durability, something they weren’t willing to sacrifice, so the spindle size had effectively been maxed out. This problem gave birth to the external bottom bracket system, which moves the bearings of the bottom bracket into cups which sit outside the bottom bracket shell of the frame, allowing for large bearings and a thick spindle within the traditional bottom bracket shell dimensions. Remember that up until this point, in traditional square taper, Octalink, and ISIS set-ups, the spindle and bearings were all housed WITHIN the bottom bracket shell of the frame. Moving the bearings outside the shell created more room for a larger spindle inside, so external bearing bottom bracket systems can have both larger spindles and bearings than their traditional counterparts.

Spindle diameters could suddenly go up to 24mm, which made them stronger and stiffer than ever before. This was a MAJOR improvement, and created a much stiffer crankset/bottom bracket set-up, which is being widely used today. Almost every manufacturer has brought their own brand of external bottom bracket systems to the market; popular models include Shimano Hollowtech II, Race Face X-type, FSA MegaEXO, and Truvativ/SRAM’s Giga X Pipe (GXP). These external bottom brackets are probably the most common type of bottom bracket found on bikes in today’s market. Each brand’s external bottom bracket system is fairly similar, and most have also designed exclusive crank/bottom bracket product lines based on external bearing bottom bracket designs.

It should be noted that Campagnolo’s Ultra Torque crankset/bottom bracket system uses external bearings, but each crank arm is permanently attached to one half of the spindle, and they are joined in the middle of the bottom bracket shell, the only bottom bracket to do so.


A Campy Ultra Torque bottom bracket.



A crankset which uses the BB30 design standard.

A crankset which uses the BB30 design standard.


Thought that was it? While external bottom bracket systems are still relatively new to the market, there is still more change on the horizon with the BB30 standard. Debuted by Cannondale at the 2000 Tour de France, the BB30 system starts from the frame up, using a larger-diameter bottom bracket shell sizing to create more space for an even larger 30mm diameter axle, 6mm thicker than the 24mm steel axle used on external bearing systems. (The traditional inside shell diameter was 34mm, BB30 uses a 42mm inside diameter.)

The BB30 system is also unthreaded; the bearings are pressed directly into the shell instead of sitting inside of cups threaded into the frame. This saves weight, because it eliminates the need for some parts, like the threaded cups. Even the threads that they require to screw into the shell add some weight.

Similar to the ISIS concept, BB30 is an open standard. Cannondale initially developed it as a proprietary technology, but saw the potential for the set up and wanted to avoid some of the mistakes made by Shimano with their Octalink system. Thus, it was published as an international standard, and is now free for any manufacturer to use and develop.

Many experts in the industry see a bright future for BB30 systems, as they are the stiffest and lightest to hit the market thus far, and perhaps more importantly, the technology is equally available to every company, making it a good contender for worldwide acceptance. As for now, this system is mostly reserved for higher-end bikes. In addition to a new bottom bracket shell, cranks must be manufactured to work with the BB30 system, so options are still limited. SRAM and FSA are some of the early adoptors of this technology. SRAM offers their Force, Red, and XX cranksets with a BB30 option and FSA Gossamer, Afterburner, SL-K and K-Force cranksets also have a BB30 option. While it does provide a significant performance increase, frame and crank manufacturers must design new frames around the larger shell size of the BB30 standard, and it will most likely be a few years before the larger shell specs trickles down frame manufacturers’ product lines.


Some frame manufacturers like Scott, Trek, and Giant have tried to take the BB30 system even further, creating the “integrated bottom bracket.” This system requires yet another new bottom bracket shell sizing, designed around the diameter of bearings in existing external cup bottom brackets. The technology behind BB86/90 systems is similar to BB30, but it is designed to be used with existing external cup, two piece cranksets. Just like BB30, bearings are pressed into the shell, eliminating the need for cups and threads, and again, eliminating more weight. BB86 and BB90 get their names from the width of the shell (86mm and 90mm wide), while BB30 got its name from the 30mm spindle diameter. Shimano’s own adaptation and proprietary interpretation of this technology is called the “Shimano Press Fit” bearing system. Shimano has not yet adapted any of their products to the BB30 system, and is instead investing its resources into its incompatible Press Fit systems.



This eccentric bottom bracket would allow the spindle to move around inside the bottom bracket shell to achieve perfect chain tension.

This eccentric bottom bracket would allow the spindle to move around inside the bottom bracket shell to achieve perfect chain tension.


Lastly come the eccentric bottom brackets, which are used almost exclusively on single speeds, fixed gears, and tandems. These setups allow the bottom bracket to slightly rotate in order to adjust chain tension without moving the rear axle.

Get Your Bearings

Ceramic bearings have made quite a splash in the high-end market recently as a lighter, stronger, and smoother alternative to steel ball bearings. While they do tack on a few extra bucks, most agree that there is a performance increase in ceramic bearings. Some high end models come with ceramic bearings, but aftermarket ceramic bearing cartridges can be purchased in a variety of sizes from several manufacturers.

Looking Ahead

Bottom bracket technology will be a constantly evolving area, and we are most likely rather far from developing a lasting standard. Much like the headset, constant and quick innovation will drive introductions of newer, better standards as engineers develop better products and materials. The bottom bracket wars are far from over, and it seems to be only a matter of time before the current technologies become largely obsolete, giving way to stiffer, lighter, stronger designs.

Take a deep breath. For the moment, anyway, you can consider yourself up to date.


  1. Matt on

    Thoroughly enjoyed this brief synopsis of the bottom bracket. Would enjoy more similar to this regarding other bike parts/components, etc. Thanks for the education. Matt

  2. Jeremy Quay on

    The Octalink system had several advantages; it created a stiffer interface, giving the rider more power transfer from their legs into the mechanical system of the bike, much more than a square taper bottom bracket.

    Are there any measured numbers, showing how much is “much more” in this case? So that we are all sure here that this is not just a marketing brainwashing 😉

  3. Matt on

    Come on Jeremy, who needs objective data? Probably wouldn’t understand the statistical analysis of the research performed on the material anyway. That’s for grad students who need trivial projects to complete their degree. WIth a little EPO and octalink, the power transfer really is greater. (But you bring up a good point.)

  4. Cozy Beehive on

    “The Octalink system had several advantages; it created a stiffer interface, giving the rider more power transfer from their legs into the mechanical system of the bike, much more than a square taper bottom bracket.”


    It also broke on several occasions. Here’s an example of a shearing failure : Supposedly, there was a small amount of torsional backlash in the splines that worked the retaining bolt lose to the point where insufficient engagement cased a rupture. I recall someone’s comment (can’t figure out where I read it) that he crushed a cartridge BB and found the spindle to be stepped down from the diameter at the ends and the bearing race was cut further into the spline. Stress concentrations?

  5. Cozy Beehive on

    Perhaps not everyone needs a 30mm spindle to begin with. If you’re make like a German sprinter and you know you’re going to pound on that bike every so often, sure. Bigger spindles transfer the same torque with less stresses. If you’re a puny guy simply biking for enjoyment, you don’t necessarily need to shell an extra half grand or whatever it is for fancy bottom brackets.

  6. BradSohner on

    Very good point, Cozy. It should be noted that there were several reports of Octalink durability problems that hurt its reputation and probably contributed to its eventual downfall. Lots of reports out there of premature wear because of the smaller bearings needed for use with a larger spindle.

  7. Octostink on


    I have never seen an Octolink spindle break like that square taper spindle you have posted. Do you have a photo of an Octolink spindle failing in that manner?

    The main issues that I am aware with Octolink is spindle/crankarm interface wear.

  8. LCP on

    I agree with beehive. The Shimano splines have a tiny bit of rotational slop which cannot be eliminated no matter how tight the bolt is. Pedaling works the bolts loose on a regular basis and you pretty much have to carry a large hex key with you. I think Shimano made a design blunder by not tapering the splines so that you could achieve a dead-solid fit when the bolt is tightened. that was the nice thing about the square taper system of old. Of course, I don’t think the isis system is tapered either. I personally think they all would benefit from a taper fit spline. It’s a bit more difficult to produce but It makes a better connection.

  9. Ron C on

    To Note: BB90 is a Trek only standard that does not use external cups. The bearings (which are spec’ed to fit a 24mm external BB spindle)press directly into the carbon frame similar to a BB30 system except for the fact that a BB90 is “90”mm wide and a BB30 bottom bracket is 68mm wide for road and 73mm for MTB. (also the BB30 bearings are bigger in race OD and ID)

    I believe you have BB90 confused with the shimano BB91 (or BB92 in MTB circles) which is a nylon reinforced cup which is pressed into the BB of the frame. The BB91 standard comes in a few widths for BB which are 86.5mm width for road which in the end after the cups are pressed in become 90.5mm (hence BB91?….yah confused yet…just wait) The MTB BB92 kit which either works with a 89.5mm or 92mm width and this depends on whether the manufacturer wanted to run the BB asymmetrical or symmetric due to using a E-type derailluer or not.

    So depending on what manufacturers bike you purchase and what BB koolaid they have drank you might want to know this information before you leave the shop and make sure you marker it in on the underside of your top tube…this is so when the poor mechanic/parts counter guy comes to deal with you and a new BB you will at least give him a heads up on what they are dealing with and they can get you set-up in a timely less frustrating manner.

  10. Jean on

    This is a useful article with good pictures.

    I agree with most of it and appreciate that it points out the old Ashtabula system was strong. Your department store 10 spd example does not suggest this, but the early BMX bikes with their CrMo one piece cranks and their higher ball-count, more precision, pressed in bottom brackets could take garage roof drops that totally flattened a top quality pair of wheels in one drop. No aluminum set up ever matched that strength.

    I do question the use of the term “loose ball” to express what should more accurately be called “three piece” cranks. In fact your own example shows that three piece cranks used the same type of “retainer” bearings as did the Ashtabula.

    You can be excused for missing the tangent of hollow BMX crank development including the Red Line Flight system.

    Thank you for mentioning the innovations that Cannondale and Alex Pong (Magic Motorcycle) brought to the story.

    I do think that missing “cottered cranks” is not acceptable. That is surely the great grand-father to all that has followed.

    That cottered crank was the rest of the world’s system at the time Schwinn and all the other American bike manufacturers where using the Ashtabula (ohio,btw) one piece crank. Anyone interested in keeping a classic bike classic might find this necessary information. Working with them can be tricky, the most important things to know is. Drive the pins in, don’t use the treads to pull the pins tight. You probably won’t be able to use a pin once you remove it but by now that might be a necessity. There where about 8 different pin diameters/ and bevel tapers, so matching pins and pins orientation to each other was important. J&B imports still has many of the sizes.

    All in all, nice web content. Wish I had done that.

  11. Alan puzarne on

    Has anyone had a problem with creaking from bb30. I am purchasing an orbea orca currently have easton ec90 crankset and bottom bracket. Can’t decide whether to us with sleeve or move to SRAM BB30 crankset. Any advice is appreciated

  12. Eric in Boulder on

    I’ve been riding since the ’60’s, and have seen the up and downsides to the evolution of BB tech especially. The trade-offs between utilitarian/tourist oriented design thought, versus pure racer’s priorities, is a constant source of aggravation. It is my opinion that except for the weight issue, many “advances” have been poorly executed, and the BB is perhaps the worst.
    The older steel BB spindle and adjustable outer races were notoriously easy to contaminate, and they’d need overhauling after one rain ride. However, the integral sealed unit that was the standard until the “outboard” bearing and large hollow axle, may have been the best with longevity and cost- I’m still riding a mountain bike w/ 10year old Shimano BB, and it spins far more easily and smoothly than either a Campy UT, or an FSA mega-exo w/ Enduro ceramic upgrades.
    Maybe because the one-piece unit can align and protect the two bearings far more accurately, while the sloppy tolerances of facing the BB shell, along with the klugey methods used to seal and position the newer style make it more likely to have binding, twisting, and side-loading issues regardless of how much better the bearing itself might be. Most have extra washer-like “seals” crammed in between the bearing and the crank arm, but this only seems to be a trap for dirt and water, not a seal at all. The bearings should have minimal side loading, unlike a hub bearing, yet adjusting the final fit involves shims, loctite, etc. and an impossibly accurate facing and width requirement, that unfortunately today one shop in 100 may have the tools and a mechanic who knows what to do wtih them.

  13. Graeme on

    The *need* for increased rigidity in the bicycle for most users is debateable to say the least – the *need* of component manufacturers to come up with reasons to encourage unbridled consumption to keep all of those factories out there churning and burning is, however, not at all debateable!

    My own feeling as a mechanic and a rider, who spends a lot of his time talking to enthusiast riders, is that many have been seduced by the technology, without considering whether it is the right technology for their purpose. This is true right the way through, from frame design to wheel construction, including (appropriately enough as it is called the “Central Movement” in many languages) the BB.

    Many of the technological “advances” that we see are a re-hash with better materials of old ideas, carefully spun to make them attractive to consumers, often implimented to reduce production or assembly time & therefore cost, but often marketed at premium prices in order in part to defray the costs of persuading consumers to make a change.

    BB technology, I’d contend, is no different in this respect. The current divergence in choice is not helpful to anyone, and the “advantages” supposedly gleaned are of no practical use to 99.9% of the users out there … it’s easy for those of us involved in the very-serious-leisure-to-racing side of the market to forget that our special interest forms an insanely small part of the market.

    I think it’s that element that is missing from the otherwise excellent (even if it does miss out cottered systems) set of notes above.

    BTW, you are (sadly) only too right about the durability problems of outboard systems, exacerbated by the lack of tooling / training in the use of that tooling for facing & chasing BB shells … we run a course in frame preparation at my company, and the number of supposedly experienced spanner-monkeys that we have to go back to basics with in terms of concepts like concentricity, parallelism and tolerance in thread design and execution is scary ….

  14. Doug Kon on

    BB91 vs. BB92
    Ron, or whoever…….
    I need a new BB for my 2008 Pivot Mach 5.
    My shop has a BB91 instead of the spec’d BB92, but Pivot owner Chris Cocalis says it is OK to use BB91.

    “….. no issues as long as you do not run the spacer. ”

    Is this true? Would you feel cool with the BB91?
    Local Triad, NC rider.

  15. Mike on

    Are there any adapters that exist that can convert the standard english threaded frame BB housing to use the BB30 crankset?

    I have a new set of BB30 cranks but I still want to use my old frame. Any recommended options?

  16. Will on

    –>Mike – No. BB30 has a 30mm spindle. . . all of the old “standard” (english/italian) bottom bracket styles were built for 24mm spindle.

    To play devil’s advocate for the side of new technology (vs. the old traditionalist super shop guys). . . I agree, a lot of the new products out there re-package old ideas and are sold for a higher price. I also believe that a lot of people buy the wrong bike for themselves. . . they see the tour and want the racing style bike when what their legs and back really need is a “paris-roubaix” style bike (or maybe even a hybrid). That being said. . . the amount of trickle down technology that comes through all of the constant performance oriented engineering is significant. The amount of features that a person can buy on a 400 dollar bike today is far beyond what they would have been able to 20 years ago (dollars adjusted for time). I agree that some of the technological advancements do not suit the great majority of riders, but if the rider can slow the purchasing experience, they just may end up with a great bike that borrows a lot of good technology from our performance oriented engineering industry.

    ps. I have never had any problems with external bottom brackets. I put them on the bike once (properly), ride hard, in the rain, across the country, pushing my heavy 210 lb body up hills/mountains, and have never heard so much as a creak, let alone had to tighten it or take the whole thing apart.

    pss. the only bottom bracket left off of this forum is the new FSA/Wilier/BH BB3865. . . 30mm spindle, 86.5 wide

  17. yingwai lee on

    Does anyone know what is the difference between Shimano square taper bottom bracket UN26 and UN54.
    How to identify the bottom backet on my bike is English thread or Italian thread.
    Thank in advance.

    LEE YW

  18. Lou P on

    I have a 1980 DeRosa bike w steel frame, had loose Campy bottom bracket w italian threading…..can I convert this bike to use an Outboard bearing bottom bracket? If so, which options do I have?

    Thank for your assistance,


  19. Marcelo Zattarin on

    Buy a frameset Scott Plasma Premium and this goes a botton bracket BB91 Press Fit
    The question is: to continue using my FSA SLK MegaExo Ligth cankset shaft diameter 24 mm. I used these with a botton bracket BB8681
    That botton bracket should I buy?
    I prefer ceramic

  20. Sonny on


    Guys please can i have your using fsa pro team issue cranks and an ISIS BB type. Now, i want the left arm of the crankset fitted or latched snugly like shimano with cups outside the BB shell. I just want to hide the remaining space from it to keep it tidy and neat without seeing a small amount of space on the arm. Is it possible of having those kind of housing in an ISIS BB?

    Can you recommend whats best solution please.

    Thank you.


  21. sean on

    My new frame has a BB30 bottom bracket with no threads, but my old one was a regular GXP (BSA?) screw-in type – so despite having a spare BB I’m still stuck.

    If I understand correctly, there seems to be various adapters out there (esp. Wheels Manufacturing, and Endura) allowing you either: to press-fit an adapter then screw-in your old GXP BB; or to use regular BB30 bearings then a shim to allow your GXP crank to fit.

    Both would let me use my GXP crank on the new frame somewhat more cheaply than an equivalent new SRAM crankset for BB30… but is it worth it? Am I better off biting the bullet and just buying a full BB30 crankset to get the most of my frame?

    Thoughts welcome!

    following links may be useful to others:

  22. Confused on

    Can the article be amended ? to include info on whether the spindle length has to match chainset.

    i.e Shimano techdocs state a certain spindle length for a certain chainset but in most cases the length of recommended spindle is different from the previous bottom bracket spindle. Surely chainline will be affected.

  23. Simon White on

    Two corrections:

    1) You missed out cottered cranks! Their BB axle has a single flat at each end and a tapered flat-sided pin was wedged in against the flat. They were the standard for a great many years in most of the world.
    North America was much more inclined to the Ashtabula/onepiece crank, I don’t know the history of cottered crank there.

    Ignoring the still-substantial share of onepiece cranks, global market share for new cranks was given in 2012 as:
    80% square taper
    20% cottered,
    10% ISIS and all the modern designs.

    2) French and Swiss BB threading is long-gone. I read that Peugeot switched from French to Swiss to English over the period 1978-1984 or 86, and I know for sure that it was 1984 until all of their top models got English threading in all markets.
    re “Confused – 01/07/13”, on why the recommended modern replacement for an old discrete BB may be longer than the original:

    Older cranksets often required a BB which was 1-8mm longer on the drive side. (I guess this was originally to allow use of a single crank casting/forging for both sides, the driveside one then having a spider or chainring swaged onto it). The discrete BB axle will have a code stamped into it e.g. “3P”.

    Modern cartridge square BBs are pretty much symmetrical, though some of the longer ones have an extra mm on the drive side.
    So when replacing an assymmetrical discrete BB you often have to use up to a 2mm spacer on the drive side, which would require a BB 4mm longer than the original to achieve symmetrical pedals.
    In order of importance consider
    1. chainstays – the cranks must not hit.
    2. Chainline.
    3. pedal symmetry and width apart, which affects your leg joints and cornering clearance.

    Feel free to update the original article from this.

  24. Jason on

    A very interesting read indeed, I thought this article would have what i required for a Tandem i bought for £45, as a home project but also to have some fun and ride the London to Bright with a work colleague.

    There seems to me there is an interface missing from the article. I have got two bikes where the BB axle has a ‘cut out’ section (not sure of the technical name), to fix a crank to the axle you place the crank over the axle and line up a circular hole in the crank with this ‘cut out’.

    Once lined up insert a metal tapered shim and place a bolt on the end which tightens the crank into place, this is what i have on the bike but finding replacement parts is a nightmare at present.

    In summary there is no note of this within the article, but it is out there, what is this interface and where did it come from, also where can you get replacement parts (if any)?

    Any help would be appreciated, I could just replace the BB and the crank-set, this will not only increase the cost of the project, but detract from the originality and i would prefer to have this.

  25. Jason on

    Okay i did not see the last posting….[embarrassed face], result, read all comments in future.

    Thank you Simon White, I have something to go one now and further investigate!!

  26. qboasso on

    Just found this great read.. much easier than wikipedia’s article to understand. Could I somehow replace my square taper shimano bb and us a BB30 crankset (sram force)?

  27. Nazmi on

    My Colnago Strada SL frame currently use BB 1.37×24 with shimano ultegra hollowtech 2.
    My question is :
    1. Is it right if i get ISIS BB , i had to choose 73mm English 108mm(road) ? or the 68mm ?
    2. If i get an FSA light crank, WHICH FSA crank i had to get in order to install correctly on my frame? BB386 ? MegaExo ?
    3.Which crank can get slip inside shimano BB Hollowtech 2 other than shimano crank ?

  28. Diego on

    The beauty of the bicycle – and what gave it acceptance and popularity – was simplicity and serviceability. Not as an experiment, but in the course of overhauling a Raleigh-built 531 road bike, I replaced the bearings (yes, loose) of Dura-Ace BB, hubset, and headset with precision chrome-moly ball bearings (yes, loose) of the correct sizes and packed them with high-load silicone bearing grease. After adjustment, the bike was put back on the road. Two years later, after about 1500 miles of New England riding including hot, cold, and wet days, it seemed time to take a look at the bearings again.

    Surprise! In all instances, the bearings and races were immaculate. There was no discernible evidence of metallic shedding (usually noted as a blackening in the grease) nor breakdown from moisture. Again, these were road miles and not particularly aggressive. But the demonstration was that good fundamental design and material quality provided trouble-free cycling at a small fraction of the cost of endless re-engineering.

    Today’s cyclists are faced with costly and ever-changing componentry in pursuit of the ultimate in light weight and an intractable proliferation of “standards.” We cyclists and cyclist-mechanics have lost something very special to the sport of recreational cycling. While new designs may, in fact (in engineering and advanced power transmission testing), be improvements for extreme users the benefit to most cyclists is fanciful. Keeping a comfortable cycle operating efficiently and economically has been traded for “the latest” output of a profit-minded manufacturing sector. A shame, really.

  29. Dave on

    Great overview of the bottom bracket quagmire for novice mechanics like myself.

    This piece has cleared up a lot of the more confusing aspects of all of the different technologies for me and the historical frame this round-up is built on put everything in an easily graspable context.

    Thanks for this, I will now be able to buy myself parts for my bike re-build with a bit less uncertainty.


  30. Pieter on

    I have a Giant XTC 27.5 (2014) and now I’m looking to replace the crank. At the moment I have Shimano Deore Hollowtech II. The problem I have is I don’t know how to find out if I have 68/73 or 83 shell width and I can’t find a answer anywhere how to find out what I have. The only information I have been finding is that it exist. The Giant website only say that it is press fit and when I find information about Hollowtech, they only talk about threated brackets and not press fit. How can I, without disassemble the bike, know which shell width I have? Or doesn’t this matter looking at the crank and does this only matter when changing the bracket?

  31. Richard Holroyd on

    The problem I have with square-taper fitting is getting the cranks off because the aluminium cranks stick to the steel axle. If I try the standard removal tool which screws into the boss of the crank, all that happens is that the soft aluminium threads in the crank are stripped off. Using a couple of hefty bolts and some bits of old 1/4″ steel I have improvised an extractor, but crank removal is still a major job. I’m going to try an ISIS splined system which I hope will avoid the removal problem.


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