Bottom bracket

[2] American bicycle mechanic and author Sheldon Brown uses axle once and spindle four times in his bottom bracket glossary entry.

Many bicycle brands have introduced their own dimensions for bottom bracket bearings,[5] and the different use of terminology by the various manufacturers has been described as confusing.

Sealed cartridge bottom brackets are normally two pieces, a unit holding the spindle and bearings that screws into the bottom bracket shell from the drive side and a screw-in support cup (often made of light alloy or plastic) that supports the spindle and bearing assembly on the non-drive side.

The design is similar to a typical hub bearing and theoretically supports the load better but is hard to seal effectively against dirt and water.

The sales pitch of these systems have been to enable reduced weight and increased stiffness compared to internal bottom brackets.

They also offer more distance between the two bearing surfaces, which contributes to stiffness while allowing lighter components (but also may increase the Q factor).

The terms 'X-Type' and 'Hollowtech II' are both used to refer to any design of this type, but are in fact trademarks of the corporations marketing the systems.

With this new standard have come several cranksets designed to use the external bearings of other manufacturers, such as DMR's "Ex type" and Charge Bikes "Regular" cranks.

In the early 1990s at Magic Motorcycle, a small USA component manufacturer later purchased by Cannondale, and re-formed into Cannondale's CODA brand (Coda Magic 900 cranks), made a proprietary external bearing bottom bracket, oversized spindle and crank system.

However, Cannondale moved on from that system and developed the SI cranks and the new BB30 unthreaded press-fit bottom bracket standard.

BB30 requires special frames which have a 42 mm diameter unthreaded bottom bracket shell (which is larger than the 34.9 mm threaded ISO standard threads) allowing use of internal sealed bearings while their top level SI crankarms are still two machined aluminum halves glued together.

Another precursor of the current external bearings/through spindle design was developed by Sweet Parts, a micro-manufacturer of high end cranks and stems.

[11] Bicycle frames utilizing pressed bearing standards do not have any threads inside the bottom bracket shell.

A disadvantage is that assembly and disassembly of press-fit bottom bracket bearings require expensive special equipment.

A third disadvantage is that there has become a wealth of competing and incompatible press-fit bottom bracket standards introduced by various bicycle manufacturers.

For PF30 (SRAM), BB86 and BB92 (Shimano), BB79 (Cervelo), and BB386EVO (FSA) the bearing is housed in a nylon plastic cup that is pressed into the frame’s bottom bracket shell.

Lightning Cycle Dynamics, Inc. offers a carbon crank bottom bracket assembly[15] with semi-axles that connect in the middle via a hirth-like joint to form the spindle.

The problem is that normally the interface cannot be tightened enough without a cotter pin press, a highly specialized type of clamping tool,[19] though still produced and for sale.

Cotters can also be installed with an improvised tool designed for another purpose, such as a ball joint splitter or hammer, with mixed results.

The ISO size is primarily used by Campagnolo and other European manufacturers, in addition to cranks that adhere to the Nihon Jitensha Shinkokai (NJS) keirin standards (Sugino 75).

Several manufacturers have built bottom brackets with titanium spindles and alloy cups but their durability was lower than that of steel.

In recent years Shimano has migrated much of their product line away from square taper to a spline attachment called Octalink and to external bearing types.

Shimano 105, Ultegra 6500 and Dura Ace 7700 cranksets mate to v1 spindles, while later mountain bike designs use the deeper-grooved v2.

Spindles come in a wider range of lengths (102–140 mm [4.0–5.5 in]), and are sized to match not only the shell width but also the type of crankset it will support (longer for triple, shorter for single, etc.).

Some manufacturers (like Trek) are starting to implement this into their bicycles, while it is also possible to have threading cut into an existing 46 mm pressfit and have T47 cups fit in there.

In a fixed-gear bicycle, the bottom bracket should be high enough to prevent the pedals from coming in contact with the ground while cornering but is not always achieved.

This caused aftermarket brands to struggle in creating a bottom bracket that would fit into bikes that came with OEM Shimano parts.

Companies such as RaceFace, Chris King, and Truvativ (SRAM Corporation) sat down in 1998 and collaborated on a standard bottom bracket specification.

In August 2001, the ISIS Drive Standard was published and made into open source for anyone to create products using the designated specifications.

This success would prove to be short-lived due to failures and need for the industry to continue progressing and creating better specifications.