Bottom Bracket Types
In the bicycle industry's relatively recent past, we've seen many different types of bottom brackets become available. As with many advances in the industry, there are as many reasons for these changes as there are new standards. Frame builders want to make lighter, stiffer frames. Some component manufacturers want to create an ideal, universal design. Others want to protect their own proprietary designs. Here's our rundown...
Threaded Bottom Brackets
Almost every bike frame made before 2008 used a threaded bottom bracket. Threaded systems can use internal bottom brackets (ISIS, square-taper, or Octalink) or external bottom brackets (Shimano Hollowtech, SRAM GXP, Campagnolo Ultra-Torque). English (BSA) and Italian thread configurations are available, and are not cross-compatible. Very few frames have been made with Italian threading since the early 2000's or so.
These various innovations were more or less efforts to make a larger spindle and adequately-sized bearings work together for stiffness, strength, and more efficient power transfer. Eventually, manufacturers began experimenting with bigger changes.
BB30 / PF30
Cannondale introduced BB30 in 2000, and it's since been adopted by many manufacturers. This standard is built around a 30mm crank axle-hence BB30. Originally, BB30 referred to a threaded system, but these days it's somewhat-confusingly used interchangeably with PF30, which refers to a press-fit system with similar dimensions.
In any case, the innovation involved here was giving the BB shell itself a wider diameter, making more room for the spindle and bearings. BB30 is an open standard, meaning it's free for any manufacturer to use—and as a result, it's taken off. Actually, PF30 has pretty much taken over from BB30 at this point.
Trek's innovation with the BB90 standard was to build the frame out over the bearings rather than keep them outside of the BB shell. They made bike frames with down tubes that extended out to a bottom bracket shell 22mm wider (11mm on each side) than the previous 68mm standard. The result was an incredibly strong frame in the bottom bracket area, plus fewer pieces to worry about. BB90 is a press-in system, with a pair of bearings that are pressed into the frame, and that's it. "90" refers to the width of the BB shell (68+11+11), in millimeters. The spindle diameter and bearing size is the same as in traditional threaded systems.
The PF92 standard, used by Scott, Giant, Pivot, and other companies, is very similar to BB90 except that it uses PressFit technology, in which the bearings are pressed into composite cups which are then pressed into the BB shell. This allows for slightly less stringent manufacturing tolerances, making this system popular for use with aluminum frames.
BBright is Cervelo's standard. They picked their favorite parts of BB30 and BB90, and used PressFit technology to boot. BBright has the larger-diameter spindle and BB shell of BB30, plus a wider shell width like BB90-but only on the non-drive side (so, 68+11=79mm wide). This allowed Cervelo to use a wider and stronger down tube on their frames, without any effect on their bikes' chainlines.
FSA's BB386 standard is similar to BBright in that it uses a wider 30mm spindle and a wider BB shell—but in this case, the shell is a symmetric 86.5mm wide. In theory, this allows for the stiffest and strongest frame of any other option, and as a bonus, this standard uses the same bearings and cups as PF30 and BBright.
The BB type that your bike uses will affect what kind of crank you can install, though many options are generally available for any given BB, and some manufacturers make adapters to make otherwise incompatible sets work together.
Bottom bracket overhauls and replacement should only be attempted by an experienced mechanic. Improperly installing a bottom bracket can easily ruin a frame. New frames often need to be "faced" before bottom bracket installation; this should only be done by an experienced mechanic with the proper tools. As always, if you have any questions about compatibility or anything else pertaining to your bottom bracket, please contact us at [email protected] or 1-800-682-0570.
Oh, and - Ceramic Bearings
Research has found that ceramic bearings are more efficient and more durable than their steel counterparts. Ceramic bearings have 5-10 times the durability of steel bearings, are 10 times rounder, 20% stiffer and weigh 40% less than steel. Their hardness is much greater than steel's—they literally pulverize contaminants. Choosing a BB with ceramic bearings, or upgrading your current system, can make a big difference in your bike's performance. For more information, check out our article on ceramic bearings.