Bottom bracket

With internal storage, also called the bottom bracket, the bearings are collectively referred to on the bike, where the bottom bracket is mounted on the turn are attached the cranks. The bottom bracket is the most heavily loaded bearings on a bike. The forces acting on the wave forces exceed even the loads comparable with a crankshaft of the internal combustion engine of an average vehicle. The term "internal storage " was established by the former bicycle mail order company Brügelmann. Usually, an inner bearing from at least two bearings which support the bottom bracket to the left and right end of the bottom bracket shell.

Like other bearings, the bottom bracket of a bicycle used to contain so-called cones bearing, in which the balls between a fixed and an adjustable tread ( the cone ) rolled. Today, this kind of bearing is increasingly being replaced by so-called industrial bearings. It is rolling bearing in which balls ( rarely also rolls or needles ) form and their treads an inseparable unit.

• 3.1 wedge mount
• 3.2 square cone
• 3.3 hexagonal cone
• 3.4 multitooth
• 3.5 Fixed connection to a crank arm
• 3.6 Fauberlager
• 3.7 Other

Fixing the bicycle frame

Inner bearings are pressed or screwed into the bottom bracket shell of the bicycle frame. The following table gives an overview of the major dimensions of the fittings or threads and the width of the bottom bracket shell.

Rare 83 or 100 mm

• The types of attachment in the first half of the table up to and including Fauber - camp were originally in classical cones bearings ( see below). Today, the bottom bracket shell of this kind are but mostly equipped with cartridge bearings. The attachment types in the second half of the table are not intended for use with cones camps, they are generally fitted with sealed bearings.
• ENG and FRA are to be distinguished sometimes ambiguous. Here, the only careful experimentation.
• Bells stock had a square (or hexagon ) Recording for the cranks and the typical striking curved, usually chrome dust caps. They have been replaced by Thompson Bearings with first wedge attachment and later also square mount the cranks and square dust caps. Balls are used with 1/ 4 inch (6.35 mm) in diameter.
• Right bearing with right-hand thread should be medium strength with thread lock or a lock nut back up.
• Wavelengths at bottom brackets with integrated shaft ( cartridge bearings): 103 - 107-110 - 113-116 - 119-122 - 132; Intermediate sizes possible
• Housing according to BB30 and PF30 are provided for BB30 cranks, but can be reduced for other systems.
• OS -BB- BB shell are not compatible with BB30 cranks, but can also be reduced.

Bearing types

All interior bearing types are roller bearings in principle and consist of two camps, one located on the right and the other at the left end of the bottom bracket. The technical development of the bottom bracket proceeded in three steps from the cone bearings to roller bearings ( bearings) and the chamber. There are also other, less common solutions such as the camp.

Classic conical mounts

The bottom bracket spindle, and the two cones form a unit. The bottom bracket cups are screwed into the bottom bracket shell. The balls are positioned by a sheet metal cage ( bearing cage ) and run directly between the cone and the bearing shell. Bottom bracket in this design are maintenance- consuming. However, since they are adjustable, they can theoretically achieve a higher mileage than cartridge bearing with deep groove ball bearings with good care and quality materials. Bearings of this type require a precisely machined bottom bracket shell with parallel outer surfaces and a manual adjustment of the bearing clearance. Therefore, these bearings are no longer used in the mass production. A further disadvantage is that these bearings are not sealed to the frame interior. Thus, water can, which has come into the frame, run in the bottom bracket and there in the course of time, wash out the bearing grease and cause corrosion. The dreaded by cyclists cracking bottom bracket is a clear indication for an urgent maintenance or malfunction of the bearing.

The bearing clearance is usually set by the extent this is screwed into the shell until the axis only has a minimum clearance at the bearing cone on the left bearing cup. By tightening the lock ring must then vanish this small game without that by too strict settings when turning the cranks could already notice a resistance. The other, non-adjustable bearing shell, has a collar, until its concern at the bottom bracket shell, the shell is screwed in firmly.

In many camps, the right-hand cup has a left-hand thread. Due to the changing load of the bearing shells while pedaling torque could arise namely in conjunction with the radial play in the bottom bracket shell, whose direction is opposite to the rotational direction of the cranks is. This would therefore provide in this arrangement that the bearing shells are not detached. However, this effect is less than for example with the pedals which need to be absolutely screwed on the left side by means of a left-hand thread in the crank. In addition, the fine thread of the large bearing shells affects such a large friction so that it happens more frequently that a poorly lubricated bearing shell after removing the lock nut no longer be solved, as that about a right-hand cup with right-hand thread through the flexing movement of the bearing would solve. For the same reason, it is in practice hardly that a left-hand thread on the right side or a right-hand thread screw on the left would automatically due to the high friction of a seized bearing.

Maintenance of the bearing should ideally take place before it comes to noises or binding. This includes at least one cleansing of cones and spheres, the renewal of the bearing grease as well as visible damage to the surface of spheres or treads also a change of the balls, individual cups or the bottom bracket.

Bearing shells and their retaining rings often have narrow faces with flats or grooves where tools can be used in order to solve them. The threads during assembly were not sufficiently greased, then sit shells and rings after a few years often so tight that they can be solved only with special tools or special aids.

Classic conical mounts, variant with folded- bearing cup and cone screwed

The cone bearings also include the bell bearings and its successor, the Thompson bottom bracket, in which the bearing shells are first driven into the bottom bracket shell before using shaft and ball bearings. The right cone has either a right-hand thread or is it fixed to the shaft. The left cone is screwed onto the shaft, on which there is a left-hand thread. Then follow dust cap, an intermediate ring, which is secured by an internal gear against rotation, and a lock nut.

Evident are the older stock of this kind in the great eponymous " bell " which grips from the outside through the bottom bracket shell and rotates with the shaft. With the newer Thompsonlagern these " dust cap " is much less conspicuous as it is small and flat. Also visible locknut is significantly smaller, as it is positioned on the shaft and not on the bearing shell as in the conventional conical bearings.

Typical deformation of the left side in the wrong direction chosen cotter

Deformation of the right bottom bracket bearing a Thompson

Thompson Bearings with wedge axis and impact shells

Industrial ball bearings

On the shaft are two cones instead of two fits, where deep groove ball bearings are mounted. This unit is fixed by two bearings in the bicycle frame. Compared with the classic cone bearing this design has the advantage that a go too tight inside the bottom bracket can be built by using both sides sealed industrial ball bearings ( roller bearings, deep groove ball bearings). Also for this type of bearing a precise machining of the bottom bracket is required. If no rigid spacer is mounted between the outer rings of the two industrial ball bearings, care must be taken that the bearing is not twisted when screwing the outer bearing cups into the frame. The bearing shells may only be turned so far in this case that a smooth running of the bearings is achieved without axial play. Then secure with lock ring.

Cartridge bearing

This is the type of bearing today the most widely used in bicycles. The two bearings are used by the manufacturer, together with the bottom bracket spindle into a cylinder ( cartridge ), adjusted and pressed. Result, the bearings are well protected from dust and dirt; During assembly, the bearing does not have to be adjusted. Lock rings like the bearings no longer exists. Adjustments do not fall, because cartridge bearings require no maintenance. But since they can not be adjusted, they must be replaced if a corresponding bearing clearance.

The cartridge is usually screwed with two threaded shells and a torque of 35 to 45 Nm in the bottom bracket shell, with the right screw shell is often integral with the cartridge. The cartridge chamber can be obtained with different lengths of the shaft, so that depending on the intention of the driver can vary the distance of the crank to the bicycle frame. A variant of the outer holding shells instead of an external thread having an internal thread or simply taken to be or - pressed, is used to exchange bell or Thompson bottom brackets.

The barrel chamber is the logical evolution of the bottom bracket with industrial ball bearings and spacer sleeve. Since the cartridge bearing spacer sleeve is not a loose part, but encloses the ball bearing industry, the accuracy of the bottom bracket shell is not relevant. The correct alignment of the ball bearing and the shaft to each other is guaranteed by the cartridge. Therefore, this type of bearing is used in mass production the most.

Cartridge bearings are often mounted with threaded shells made ​​of plastic in the frame. To this unscrew special tools are needed. In order to prevent a tight shell the canting, the tool should be held firmly in place, is by example, put the crank and slightly screwed. If the shaft is hollow, and a quick release can be used instead.

Outboard bearings screwed

In this, introduced in 2004 by Shimano Type the bearings outside the bottom bracket shell. The large distance between the two bearings each other to improve the ratio of stability to the weight of the structure. Such bearing are available for different housing thread, including BSA and ITA.

Unlike other systems, the bottom bracket is no unit with the inner bearing; rather, the bottom bracket is inserted through the two bearings. That is why you must be careful when installing saying that the two bearings are exactly parallel. Otherwise, the life of the bearings is significantly reduced. It is therefore essential that the bottom bracket shell face milling at both ends.

Shimano has this bearing type introduced by the term Hollowtech II or " HTII " to make it clear that both the cranks and the bottom bracket are hollow (English Hollow ). In the lower-priced groups the cranks are not hollow, so that these sets are not numbered Hollowtech II, although the same storage technology is applied. Colloquially the storage type is referred to as yet Hollowtech II. Truvativ GXP calls this type of bearing, as an abbreviation for Giga X-Pipe. In FSA Mega Exo system, this.

Constructions with external bearings generally use a certain type of connection between bottom bracket and cranks. Details can be connected to a crank arm in the section festivities.

Outboard bearings pressed in,

In this case, the bottom bracket shell has no thread, nor the camp. These are pressed into the bottom bracket shell. In the press-fit versions, the bearing is in a shell that is pressed.

Bearing BB30

Case diameter 42 mm Case Width 85/83/73/68 mm. Originally designed for indoor storage shafts with a diameter of 30 mm. The camp itself is pressed.

Pressfit30 ( PF30 )

Case diameter 46 mm Case Width 83/73/68 mm. The bearing shell ( with lying in stock) is pressed. Bottom bracket shaft diameter 30 mm.

Pressfit BB86

For road. Case diameter 41 mm Case Width 86.5 mm. The bearing shell and bearing are pressed.

Bearing BB90

Case diameter 37 mm Case Width 90.0 mm. The bearing is pressed directly. Bottom bracket shaft diameter 24 mm.

Pressfit BB92

Case diameter 41 mm Case Width 92 or 89.5 mm. The bearing shell and bearing are pressed. Bottom bracket shaft diameter originally 24 mm.

Combination of bottom bracket and cranks

The connection of the inner bearing shaft with the cranks need high torque in the rotational direction of the shaft can transmit, but also forces laterally to the bottom bracket. There are numerous systems, shaft and cranks connect to. All systems have in common that the cranks are put on the shaft of the bottom bracket, so that the lateral forces can best be transmitted.

To disconnect a puller is required in most systems, the - after loosening the screw - pulls the crank from the shaft. Some cranks have an integrated puller; in this case draws the central retaining screw of the crank when loosening the crank from the shaft.

Wedge mount

A conical wedge, which is mounted in a transversely mounted to the bottom bracket spindle bore of the crank and pressed against a surface to the inner bearing shaft. A mother secures the wedge. This method was until the 1980s, very common, but is now obsolete and is rarely used.

To remove the wedges the crank as possible from the bottom support ( or a hammer including hold), loosen the nut just enough so that its outer surface with the thread of the wedge closes and controlled with few but sharp blows, drive out the wedge.

The wedges are used: If the pedal crank in the direction of the front wheel, the mother is below. This applies to both sides. In this arrangement, the larger area of the wedge while pedaling is down, so there is where most of the force acts, the largest area.

The wedges are driven as far as is possible with moderate hammer blows. Then tighten the nut carefully. Since the wedges are made of fairly soft steel, the thread can otherwise easily be turned off. After 50 km, route the wedges again drive in with a hammer and tighten the nut.

Square cone

The ends of the shaft are four edges that taper towards the end. In the crank a matching counterpart is milled. An axial screw pulls the crank onto the shaft and keeps them there. There are two types, which differ both in the slope of the wedge and in the shape of the edges and facets, namely the ISO and JIS square. The ISO - square is found primarily among European manufacturers like Campagnolo, Miche, Mavic and partly Stronglight. According to the JIS standard, however, especially finished Japanese manufacturers such as Shimano and Suntour. Other manufacturers, such as Sugino, FSA and Phil Wood bottom bracket and cranks build both according to JIS and ISO standards.

ISO cranks do not slide far enough to JIS bottom bracket, so the risk of breakage of the crank increases ( for moderate loads, such a solution but should be sufficient ). Conversely, JIS cranks can be about 4.5 mm further on bottom bracket with ISO square plug, so it is no longer possible under certain circumstances to fix the cranks. The chain line changes in both cases.

The area between cranks and square must not be greased with Shimano and many other manufacturers in order to avoid breakage of the crank, which can occur when it is pulled too far when it is screwed onto the square. The high strength bolts with which the cranks are mounted on the shaft, but should be greased before installation on the threads and under the head and attracted strong ( as strong as it is possible, for example, with a 200 mm long allen wrench ).

The square cone was by far the most common method of attachment, but is gradually replaced by the multi-point connections, which arose in connection with the external bearings. Especially at very high quality and at sporting wheels of the square cone is now hardly used.

Hexagonal cone

For very old bicycles from the 1950s along with a bell bearing a hexagonal cone is possible.

Multitooth

The shaft end is executed vielzahnig, sometimes in addition conical. Are widespread in particular eight ( Octalink, originally from Shimano) and ten teeth (International Spline Interface Standard, short ISIS). Much less common are Power Spline with twelve and Howitzer with ten teeth and external bearings (both from Truvativ ). This type of connection is not new, but was introduced to the mass market only since 2003. At Octalink there are two different versions, which are incompatible with each other. Each other are compatible in terms of the combination of crank and bottom bracket shaft, with each Octalink cranks and Octalink bottom bracket of the groups Dura Ace, Ultegra, 105SC and XTR (all Shimano ) and cranks Ritchey and Alpina by Sugino one hand ( Octalink V.1) and Deore XT, Deore LX, Deore, Tiagra and Sora on the other hand ( Octalink V.2). The wavelengths are different; so there is indoor storage for Dura Ace, Ultegra and 105 with 109.5 mm and 118.5 mm wavelength; XTR is available in lengths of 112.5 and 116 mm.

Fixed connection to a crank arm

A crank arm and the bottom bracket is fixed to the manufacturer. The bottom bracket is inserted through the two bearings. On the other side of the second crank arm is screwed onto the end of the shaft vielzahnige.

This technique has been around since the 1980s by American small manufacturers, especially Bullseye. They were originally developed for use on BMX bikes. Shimano introduced this technique in 2004, together with external bearings.

FSA, Race Face, in 2007, Campagnolo followed this trend and the technology establishes itself in the lower-priced groups. While Shimano, FSA and SRAM / Truvativ the drive side crank arm is connected to the shaft, forming at Race Face iA the left crank arm integral with the shaft. Campagnolo divides the shaft in the middle, so both crank arms have a fixed shaft stub. In BB30 cranks with one side fixed connection between the shaft and crank it resides on the left side.

Fauberlager

For BMX bikes, there are cranks with Fauberlager. In this case, both cranks and the bottom bracket shaft are formed by a single bent piece. For such storage units requires special bicycle frame with very large bottom bracket shells, because the unit must be " threaded " for mounting through the bottom bracket shell. Subsequently, the bearing cone to be pushed from the outside by the cranks and is screwed on a thread present on the shaft. The advantage of such bearings is the extreme stability because shaft and cranks are made of one piece.

Other

Some manufacturers produce their own systems. For example builds SRAM under the brand name Truvativ Bottom Bracket - and matching cranks - called Howitzer. The manufacturer e * thirteen manufactures cranks and bottom bracket with a rounded triangular shape (polygon according to DIN 32711 - P3).

Eccentric bottom bracket

The front bottom bracket shell of tandems as well as the bottom bracket shell of a few manufacturers of durable bikes are so large that the bottom bracket can be mounted eccentrically in a cylindrical housing. This cylindrical housing can be rotated by loosening the clamping screw (s ) to set on bikes without derailleur, the chain tension. In a particular embodiment, the bearing and shaft are mounted directly in the eccentric insert ( Idworx ).

The rotation of the eccentric is less expensive than to move the rear wheel to adjust the chain tension. This is especially true in bicycles with rim brakes, because they must be subsequently adjusted.

In a tandem, the distance of the front to the rear bottom bracket can usually only be changed via an eccentric. As an alternative, therefore, would only be an idler tensioning wheel in question.

Eccentric bottom bracket are abbreviated occasionally as EBB ( eccentric bottom bracket ).

Gallery

Shimano bottom bracket Available from Shimano with BSA thread and square for the crank attachment

Shimano Octalink Available from Shimano with BSA thread and Octalink V.1 for crank attachment

Mavic repair facility Repair bearing Mavic; very expensive, but sometimes the last resort option for heavily damaged BSA thread

Inexpensive repair facility Repair bearing of Point; significantly cheaper than Mavic, same function

FAG bearing shock Bells bearing with square drive for the crank attachment

Thun JIS square taper bottom bearing, plastic adapters with BSA thread and roller burnished steel sleeve

Coreless tuna JIS square taper bottom bearings with plastic adapters and BSA thread