BOTTOM BRACKETS - An Overview

There are only a few parts on a bicycle where bearing friction develops and the parts wear out. They are headsets, bottom brackets, pedal bearings, hubs, chains, and to a lesser degree rear derailleurs. Each time they wear presents an opportunity to upgrade. In general, it's best to get the finest bearing parts you can afford to buy, so you get the longest product life.

Bottom bracket spindles provide the cone races for bottom bracket bearings and are made in three ways; forging only, forging and polishing, and machining from billet. The least expensive way is merely to forge the spindle. A mold is made for the desired spindle and hot molten steel is injected into it. Those that are forged only have a reasonably smooth bearing surface. These have no post-forging grinding and polishing to make certain that the areas where bearings touch are anything but out-of-the-mold tolerances. These forged spindles are generally all black in color.

The forging and polishing type of spindle is, in color, either Black with Silver in the bearing surface areas or all Silver (possibly nickel or chrome plated). The forged and polished spindle is easy to tell at sight, the areas on the spindle where the bearing retainers revolve appear to be microscopically scratched. Polishing is the process of making finer and finer scratches.

Billet machining is the process of taking a single piece of the metal and removing pieces of the metal (machining) until you are left with the shape you want. This billet machining process is generally performed only of aluminum or Titanium for bicycle parts.

It is considered more desirable to have a large number of ball bearings in the bottom bracket. That's why, where these bottom brackets have ball bearings in retainers, the number of "balls" is noted in the descriptions. The more ball bearings there are, the greater the surface, and the number of points, that will bear the load.

Ball bearings are found in bottom brackets in three ways; loose ball, ball inside retainer, and sealed cartridge. Loose ball (loose ball bearing) bottom brackets hardly exist anymore. This isn't to say loose ball bottom brackets aren't good, it is, in fact it's a highly desirable bearing method. It's just inconvenient. The loose ball styled bottom brackets that are still available can be considered among the best. The finish and polish on each bearing surface is done to a high degree. Loose ball bottom brackets exist only in the road racing market.

Most people are familiar with the retainer type. This has the steel ball bearings in a steel "cage" or retainer. It's convenience comes from not dropping or misplacing little balls while overhauling the bottom bracket. All the little bearings are held in place, loosely, by the retainer. Almost anyone would be frank enough to say that the retainer interferes slightly with the bearing movement, but it's not considered significant. As an alternative, some riders fill the retainered bearing cup with loose ball bearings then remove one ball and apply grease to make a loose ball bearing B/B.

The "sealed bearing", short for "precision sealed bearing cartridge," is a ball bearing retainer held in an enclosure that incorporates what would be the cup race and the cone race. The truth is a little different; the races don't really exist, the bearings are held between an outer ring and an inner ring that revolve around one another. The spindle passes through and holds the inner ring, while the outer ring is held by the bottom bracket bearing cup. Grease is packed around the inside of this bearing cartridge and a well fitting plastic seal is pressed into each side. This type of bearing requires little maintenance. In fact, when it goes out because of bearing failure or rust, the cartridge is replaced altogether.

There are two "cups" to most bottom brackets, a fixed cup and an adjustable cup. The fixed cup is located on the right side of the bike known as the "drive-side". It is a considered a fixed cup, because adjusting it would require the removal of the crank/chainring assembly. For sake of ease, when the right cup is installed, it is made snug and left alone.

The adjustable cup is on the left or "non-drive" side of the bike. It is called adjustable because the exact position of the cup for your B/B shell is unknown by the bottom bracket maker, therefore the cup is threaded in and then held by a lockring that fastens the cup in place against the bottom bracket shell.

Five Styles of Bottom Brackets are identified and defined currently being produced that have variations in design and chain line adjustments capability.

"Dual Fixed Cup with a Fixed Spindle", like an Action Tec B/B, (abbreviated in the graph as F.F), or Fixed-Fixed. These are B/B that have two cups which screw into the B/B shell all the way until the machined cup lip is tightened against the B/B shell. In essence these act like twin fixed cups. The B/B spindle lengths is the variable on the Fixed-Fixed.

"Standard" style, like the UN-71 or the Suntour XC Pro G/G (abbreviated in the graph as ST) and used largely by Japanese makers that have a fixed drive cup adjustable non-drive cup and a fixed bearing width. The bearing cone races on the spindle have a particular non-varying width.

"Internal shell - floating cups - fixed spindle", like the GT or World Class B/B (abbreviated in our graph as AI). This B/B has a spindle with bearing cartridges pressed onto it. An aluminum bearing cup threads internally within the B/B shell. Loosening one side, permits you to tighten the other side to adjust the spindle for chain line adjustment.

"Fixed spindle with Dual adjustable cups", like the Syncros B/B (abbreviated in our graph as AF). This style has a spindle with a set bearing placement, the spindle length is the variable. The chain line can be slightly adjusted though the spindle length is fixed because the cups have a separate threaded lockring. Once the cups are properly positioned the lockrings are tightened against the shell to hold the B/B in place.

The final type we call the "Dual Fixed Cup with Adjustable Spindle" like the White Industry B/B (abbreviated in our graph as FA). This design uses two cups with a machined shoulder which screws into the B/B shell until the machined cup lip is tightened against the shell. The outer surface of the spindle is smooth which permits it to slide laterally for positioning. The spindle's position is held in place by aluminum locking collars on each side which are cinched to the spindle using set screws. The advantage of this design is its wide range of adjustability.

There are two ways to fasten a crank arm to a bottom bracket spindle. It can be held by a bolt going through the arm into the spindle; or the spindle can have threads protruding from the ends, so that the arm is fastened by a nut turned down the threads, with the arm placed over the spindle. The spindles using the bolt style are generally hollow from end to end, so they are somewhat lighter than the nut type, which must be solid with threads on the end.

Many of the bottom brackets sold come with a plastic piece that fits over the spindle and between the bearing cups. The part is called a "grease sleeve", or "water sheath". This part originated when bikes were less sophisticated than they are now. At that time many seatposts were nothing more than steel tubes with a seat clamped on. Because they were open ended at the top, dirt and water that flew off the rear wheel, (you've sometimes seen where water off the rear wheel runs up the back of someone's jersey) would frequently splatter under the seat, then drop through the hollow seat post, the seat tube, and lodge in the bottom bracket. This sleeve was devised to prevent that. Many bikes now come with an alloy seatpost that is closed off at the top. Bottom Bracket makers now claim it's to prevent moisture (condensation in the seat tube) from reaching the B/B.

There are two criteria to consider in selecting bottom brackets. The first is the width of the bottom bracket shell. The bottom bracket shell is the short piece of tubing that the B/B mounts in. The shell width is measured from one side of the shell to the other in millimeters, parallel to the spindle, (not the diameter).

As a rule, all Road Racing bikes with English threaded B/B's use a 68mm wide shell, while Italian threaded Road frames use a 70mm wide shell. The 68mm wide shell is used overwhelmingly for Mountain bike frames; however some bicycle makers specifying wide rear tires that need greater chainstay clearance or makers of aluminum frames use a 73mm wide B/B shell. The 73mm width allows use the same cups, with a longer spindle that allows the designer to move the right crank farther from the bike, allowing the chainstays to splay wider to accommodate the wider rear tire. For "floating" type bottom brackets this isn't an important measurement, since the entire B/B moves, but in fixed cup type this can be a consideration. There may be occasions where the B/B shell width measurement would be helpful for the selection of replacement parts.

The length of spindle is the other criteria. It is measured end to end in millimeters, without the bolts or washers, to a few standard sizes.

English or Italian? A few Road Racing framesets come with an Italian threaded bottom bracket. However, Italian mountain bike framesets, come in an English thread. Italian threaded B/B's have a bearing cup diameter of 36mm (measured from top of threads to top of threads on the threaded part of the cup), and are threaded to fit into the bottom bracket shell with 24 threads to the inch. The vastly dominant thread pattern for bottom brackets is English (BSA). Every production Mountain Bike and Road Racing Bike sold in the USA is English thread. This is the standard that American bike interests adopted many years ago. English threaded B/B's have a bearing cup diameter, of 1.370" and are threaded to fit into the bottom bracket shell with 24 threads to the inch. We include the Italian option, when it is available, and where there is possibility it might be needed.

As aftermarket replacement bottom brackets, all those written about here are intended for use with any aluminum alloy, cotterless, crankset. All currently produced alloy cranksets have arms that are broached, (that is machine punched to conform to a particular shape), with an interior that slides onto the spindle, and has four 2 degree tapered sides. All the bottom brackets and replacement spindles we sell have 2 degree tapered ends, and are, again, compatible for use with alloy cotterless cranksets.

Since the 1992 model year (meaning parts that were first introduced in 1991), several makers of bike shift/drive components both in Europe and Japan have introduced "sealed cartridge unit" bottom brackets. This euphemism "sealed cartridge unit" is to lead the buyer into believing they are buying a B/B built with the more expensive "precision sealed bearing cartridges". This is not the case. From what we can tell they use standard grade ball bearings in a retainer, that is fit into a cylindrical steel container with ends closed off the lead one into thinking that it is a precision sealed cartridge bearing at the cylinder or "core" end. These "unitized" B/Bs (which is really what they are) do make installation easier. The rate of wear should not be considered as being much less than standard un-sealed bearings and they provide no means of access for re-greasing. If anything goes wrong with the unit, the entire assembly rather than just the bearing itself must be replaced, which at the least wasteful, at worst environmentally violent. At the rate things are progressing there may not be a modestly priced user serviceable bottom bracket other than Ritchey left on the market in a short time.

The move to Titanium replacement parts is generally accepted now, and many of the bottom brackets reviewed here have Titanium spindles. The use of Titanium crank bolts is not recommended with a Titanium spindle because the metal is un-yielding with no intrinsic lubricating quality. As you turn a Titanium bolt into Titanium threads there is the strong likelihood that the bolt will grip or "gall" the interior threads. When this occurs the bolt stops moving and seizes preventing further insertion or removal. Although Finishline Ti-Prep is made to overcome this problem, with a Titanium spindle, use an 8mm by 1mm thread pitch crank bolt of steel, or chrome plated steel, or even better, aluminum. If you use aluminum crank bolts, first use steel ones to tighten the arms on, then remove the steel bolts and replace them with the aluminum ones to hold the arms on.