The Bottom Bracket (Un) Standard

PressFit30 on the Foundry Auger w/ Sram Force Crank Bottom brackets are a part that many cyclists tend to either overlook or are completely unaware of – much less what style, shape, or size it is. The Bottom Bracket (often abbreviated to bb) is the bearing assembly that the crank arms rotate on. In recent years the choices in bottom bracket type have expanded greatly and it seems every year some new form or standard is set. It’s also a part that isn’t much thought about when it works, but when things go wrong it can ruin a day on the road or trail. If you’re building a new bike or repairing an old one, here’s a list of all the info you’ll need to determine what kind of bottom bracket you have.

The Basics

The Bottom Bracket Shell is the part of the frame where the bottom bracket is either pressed or threaded into. Most frames use the following standards:

  • Euro Bottom Bracket English: English threading (called euro in BMX) is the most common style of bottom bracket shell on bikes sold in the United States. The Shell width is commonly 68 or 73mm but may also be 83mm or 100mm on some free-ride, downhill and snow bikes. The threading on an English frame threads in the same direction on both sides so that the left side (non-drive) of the bike tightens to the right and the right side (drive side) tightens to the left. English frames are threaded to 1.37in X 24TPI
  • Italian: Italian threaded bikes are common to, well, Italian frames. Italian bottom brackets are larger in diameter at 34.6-34.9mm compared with 33.6-33.9 for English and fall in between English widths at 70mm wide. While most of the current offerings by Cinelli, Colnago and Bianchi are now equipped with either English or press fit bottom brackets, some of the classic models are still made with Italian shells. There are some custom frame builders that also like to use an Italian shell because the wider, larger diameter shell is stiffer than the English counterpart. This is beginning to change, however, as larger and more stiff designs such as BB30 have taken a foothold in the market. [Truvativ/Sram GXP BB for Italian threading]
  • American Bottom Bracket American: American bottom brackets are generally found on older bikes, low-end BMX, kids bikes, and department store bikes. They almost always utilize a 1 piece crank known as an Ashtabula crank. American bottom brackets use press in cups and have an inner shell diameter of 51.3mm. TruVativ makes a set of adapter cups to enable an American frame to accept threaded English cups. [Truvativ American to Euro bottom bracket adapter]
  • BB30: BB30 set its roots back in 1993 when Cannondale decided to think outside the shell, so to speak. Introduced in 2000 as the Cannondale SI bb/crank system, it wasn’t till 2008 that it took it’s current and official title of BB30. The BB30’s larger shell allows larger and thinner tubing to achieve greater stiffness and lighter weight. BB30 also uses a 30mm spindle to maximize power transfer that could otherwise be lost to flex. In 2008 Cannondale decided that the BB30 standard was of such significance to the cycling world that they opened the standard for all to use. Currently the largest frame manufacturers of BB30 models are Cannondale and Specialized, with Look and Niner offering it on carbon MTB models – many other brands use the standard on select models as well. FSA and SRAM/TruVativ produce BB30 crank and bottom brackets. Campagnolo also offers Ultra-Torque cups that press into BB30 frames. BB30 shells require that compatible cranks be used with the system, though with BB30′s popularity on the rise companies such as Problem Solvers & Wheels MFG have introduced adapters for use with various cranks. [Wheels Mfg BB30 to 24mm spindle adapter]
  • PressFit30 on the Foundry Auger w/ Sram Force Crank PressFit30: PressFit 30 is a new design led by Sram with the idea of improving on the BB30 system. It uses the same 30mm spindle size, but rather than pressing the bearings directly into the frame, they are contained in a nylon sleeve that is pressed into the frame. The advantage of this design is that it uses preassembled bearing/cups with integrated seals, resulting in longer bearing life. The frame design varies from BB30 in that it requires a 46mm bb shell. Like BB30 it’s based on a 68mm shell size for road and 73mm for mountain bikes. Overall the design allows for lightweight construction, narrow Q-factor, better bearing durability, simple installation and stiffer cranks.
  • BB86/BB92: This standard uses a bb shell with an inner diameter of 41mm; the road shells are 86.5mm wide and mountain shells are 91.5mm wide. The bearings are housed in a nylon sleeve that has a 41mm outer diameter. Shimano, SRAM, and FSA all make bottom brackets to fit this standard and Campagnolo offers Ultra-Torque cups that press into these frames. The big advantage of BB86/BB92 is that any standard outboard bearing crank will fit provided that the right bottom bracket is used. [Truvativ/Sram GXP BB86 Road Bottom Bracket]
  • BB90/BB95: BB90 is a Trek standard that first appeared on the 2008 Madone. It uses the same 37mm outer diameter bearings as a standard outboard bottom bracket. Like BB86 it can be used with any standard outboard crank.
  • Eccentric Bottom Bracket Eccentric Bottom Bracket: Eccentric bottom brackets (EBB) have most commonly been found on tandams to allow chain tensioning, but are becoming more common on dedicated single speed frames. The EBB system places the spindle off center allowing the it to move up, down, in and out as the EBB system is rotated, which allows for proper chain tension in a frame with vertical rear dropouts. With the widening selection of crank bottom bracket styles, more options are becoming available for EBB setups. [Problem Solvers Eccentric 46 BB for PressFit 30]
  • Mid Bottom Bracket Mid: Mid bottom brackets are quickly becoming the new standard on higher end BMX bikes. They are called Mid because at an inner diameter of 41mm they are between the 51mm American and the 31mm Euro. Mid bottom brackets use the same bearings as an American bottom bracket but unlike the American bottom bracket, which uses an aluminum or steel cup that sits between the bearing and frame, the bearings on the Mid press directly into the frame. Mid bottom brackets come in 19mm, 20mm and 22mm designs to fit most cranks out there and are the best choice if you are looking for a bottom bracket to handle a 22mm spindle and still save some weight. [Odyssey 22mm Mid BB Set]
  • Spanish: The Spanish bb system uses a similar design to mid bottom brackets but with a smaller 37mm outer diameter bearing to reduce weight. The smaller bearing isn’t as robust as those offered in mid or American options but is stronger than the threaded Euro. Spanish bottom brackets come in 19mm, 20mm and 22mm designs to fit most BMX cranks out there. [Demolition 19mm Spanish BB Kit]

Spindle Length

Spindle length is going to be determined by your choice of cranks and will affect where the crank arm is in relation to the frame.

Modern outboard systems are very easy to install, maintain and set up – however, they require that the bottom bracket be properly faced and the frame be built straight as there are no additional adjustments that can be made to deal with potential chain line issues. In most cases, it either works or it doesn’t.

With cartridge or cup and spindle bottom brackets you are able to choose bottom brackets with varying spindle lengths to achieve a proper chain line. The following spindle lengths generally work with most appropriate cranks for a given application (though this can vary depending on the crank):

  • 103mm: Track or Singlespeed
  • 108mm: Road Double
  • 109mm: Some Sugino Track and Road Double
  • 109.5mm: Shimano Road Double
  • 111mm: Campagnolo Track and Road Double
  • 113mm: Mountain Triple
  • 115.5mm Campagnolo Road Triple
  • 118mm: Road Triple
  • 118.5mm: Shimano Road Triple

The sizes listed above are only the tip of the iceberg when it comes to spindle length. Companies like Shimano make up to 15 different lengths and Phil Wood makes spindles in 1mm increments from 102mm to well over 155mm, which may be necessary to get the chain line just right on a singlespeed or track setup or because that is the spindle width that the crank manufacturer intended intended for use with a specific crank.

Bottom Bracket/Crank Interface

Not all cranks interface with the bottom bracket in the same way. The following are the most common types:

  • blogtechbb_un54 JIS (Shimano Taper) is the most common type of square taper on the market. Lower end models will have externally threaded ends that nuts will thread onto and higher end versions will have internally threaded ends and use crank bolts.
  • ISO (Campagnolo Taper) is the European standard for square taper cranks. There is about a 0.3mm difference between this and the more common JIS, resulting in poor fitment and possible damage if you try to mix them together. Campagnolo started using ISO in ’94; pre-94 Campagnolo cranks use the Japanese JIS standard.
  • JIS Low Profile is used in some older Shimano Dura Ace cranks, and is very uncommon unless dealing with the older Dura Ace cranks. Phil Wood is about the only source for a compatible spindle without finding a new old stock Shimano model.
  • tf-isis ISIS (short for International Splined Interface Standard) is a public domain standard that was created by Chris King, TruVativ and Race Face. Unlike the 8-Spline Octalink by Shimano standard which requires a licensing fee to be paid by manufactures wishing to use the design, ISIS is a 10 spline design that is open for anyone to use. Octalink and ISIS both use a larger spindle than square taper and therefore more stiff, but results in a shorter life which ultimately led to the development of outboard bearing and press in bearing cranks.
  • Howitzer is a Truvativ designed BB system based off the ISIS spline interface, though that’s where the similarities end. The Howitzer system uses outboard bearings but a 3-piece style spindle. The cranks are only compatibale with the Howitzer system because of the way they “wrap” around the outboard cup. If you tried to use this on a standard internal ISIS bb, the crank would contact the frame. This style is used primarily for more aggressive riding such as All-Mountain, DH and Freeride but has gained some popularity with the snow bike crowd due to the availability of 100mm wide bottom brackets.
  • tf-octalink1 Octalink V1 was Shimano’s first attempt at getting away from the square taper design. It uses an 8 spline design that is 5mm long and 2.2mm wide. For mountain it was only used on the Shimano XTR M952 cranks, and is no longer produced. For road it was used on Dura Ace (BB-7700), Ultegra (BB-6500) and 105 (BB-5500) with a 109.5mm version for doubles and 118.5mm for triples. Currently Shimano offers only the BB-5500 (105) as a replacement for all three levels.
  • Octalink V2 was an improvement over V1 because it uses a deeper and wider spline at 9mm (L) x 2.8mm (W) as opposed to 5mm (L) x 2.2mm (W). The two versions are NOT compatible with each other and could result in a damaged crank arm if you try to force a V1 crank onto a V2 bottom bracket. It has been offered on Tiagra, Sora, Deore XT, Deore LX, Deore and Alivio cranks and is still offered on some lower end Shimano mountain cranks.
  • tf-ck7702-4 Hollowtech II/X-Type/MegaExo: This is the most common style of outboard bearing bottom bracket the market. Unlike cartridge style bottom brackets, the Hollowtech II uses larger bearings that sit outside of the frame. The spindle is integrated into the crank arm and is 24mm in diameter. The larger bearings and spindle create a much stiffer crank. Some companies such as Shimano use two different widths for road (86.5mm) and mountain (91.5mm) cranks while others will just use the wider 91.5mm mountain bottom bracket spec for both – so it is always a good idea to check which width your cranks use if you plan on using a bottom bracket from a different brand. Shimano (Hollowtech II), Race Face (X-Type), and FSA (MegaExo) are the main producers of cranks that use this standard. Phil Wood, Chris King, Wheels Manufacturing, and ABI Enduro make some great aftermarket options.
  • GXP (Short for Giga X Pipe)  is the SRAM/TruVativ version of the outboard bearing style bottom bracket. While the outside of the cup looks identical to the Shimano, FSA or Race Face cups (and uses the same tool for installation and removal), the SRAM/TruVativ system uses a tapered spindle that goes from 24mm on the drive side to 22mm on the non-drive side. This taper eliminates the need to pre-load the bearings and allows for a one bolt setup. If you were to run a GXP crank in a Hollowtech II bottom bracket at the very minimum you would have a lot of play or binding in the crankset, and riding it could cause damage to both the crankset and the bottom bracket.
  • BB30 requires a crankset with an integrated spindle that is 30mm in diameter. The bottom bracket itself is a pair of bearings that are pressed into the frame with a series of spacers that will make sure that the crank and frame are aligned properly.
  • Ultra-Torque is Campagnolo’s answer to the outboard bearing design. Unlike other designs on the market, the Ultra-Torque has cups that thread into the frame that contain no bearings. The bearings are incorporated onto the semi axles that are attached to each crank arm, and the semi axles are joined with a Hirth Joint (a series of radial grooves that mesh together) in the center. This allows for a little adjustment in pre-load without sacrificing strength, though the downside is that precise machining is required and as a result is expensive to produce.
  • Power Spline: Power spline is TruVativ’s proprietary 12 spline bottom bracket design used on their lower end cranks. The splines make the interface between the crank arm and stronger than a traditional square taper. TruVativ is the only source for these bottom brackets.

Older Styles and Shell Types

Although some of the bottom brackets and cranks listed below may no longer be made, it’s still nice to know what is on that old Fuji or Schwinn that you bought back in college or just scored a deal on for $20 at the garage sale.

  • Loose Bearing Square Taper: Loose bearing square taper bottom brackets use the same ISO or JIS taper as the cartridge versions. However, instead of a sealed unit, the loose bearing version consists of a left and right cup, cage bearings, solid spindle and lock ring. Loose bearing bottom brackets take some skill to just but have the advantage that different weights of oil or grease can be run depending on the conditions it’ll see, allowing performance to be fine-tuned. With the open design this style does require more maintenance than sealed cartridge style bottom brackets in order to make sure they last long and spin smoothly.
  • One Piece (Ashtabula): One piece bottom brackets use crank arms that are “S” shaped and almost always fit in an American bottom bracket. The crank arms hold the bearing cones in toward the center of the bottom bracket and are adjusted by a threaded portion on the non-drive side of the bike. While still offered on bikes today they are typically limited to low-end adult bikes, kid’s bikes and some entry level bmx models. One piece cranks also almost always have 1/2” thread pedals instead of the more common 9/16” found on most cranks.
  • Cottered: Cottered cranks are no longer used in the United States but can be found on some older bikes. They use a cotter pin or sometimes a bolt to hold the crank arm onto the spindle.
  • French Thread: French thread uses a 68mm bottom bracket and the same inside diameter as an English bottom brackets, but with 35mm x 1mm and is threaded to the right-hand on both sides. These are generally found (you guessed it!) on older bikes from French manufacturers.
  • Swiss Thread: Swiss thread is the same as French thread but with left-hand on the drive side.
  • Raleigh: Used on older English made Raleighs – the inner diameter is the same 33.6 as English threaded bikes but is threaded at 1-3/8” x 26TPI instead of 1.37” X 24TPI.

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