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How to choose your bottom bracket?


Your bike creaks when you push hard on the pedals, the movement of the pedals has lost its fluidity or has become loose? The symptoms are clear: it is time to change your bottom bracket. Like all the parts that make up your bike, the bottom bracket and especially its bearings are subject to wear and tear.

Replacing it is a simple operation if it is well prepared, even if the multiplication of standards for bearings, cranksets and frames may discourage some people. Not to worry though as we will guide you through this jungle of standards. The bottom bracket is the interface between your crankset and your frame, so the first thing to do is to identify which crankset you want to fit into which frame ?

Tools required to change the bottom bracket housing

Crank handle puller

Bucket flusher

Bowl press

Removal of the case

Circlip pliers

Caliper

Clamp or pin wrench

Bottom bracket clamping ring

Identify its components

Hollow shafts such as "external bearings"

Hollowtech II
Hollowtech II 83 mm
Campagnolo
Not Italian
Sram/Truvativ GXP

Solid axes

Case type "Bottom bracket"

After extraction of the cranks by means of the extractor, this type of housing is identified by the lock nut ring on the left side.

This bottom bracket is disassembled and adjusted using a special locknut and ergos pliers.

Now obsolete, this box can be replaced by an integrated cartridge box.

Make sure here to take the same axis length that you can easily measure with a caliper.

Case type "Integrated cartridge"

After extraction of the cranks by means of the extractor, this type of housing is identifiable by the grooves of the cups.

You will need a specific tray disassembler to remove the cartridge.

There are several types of press-fitting for this type of box: Square, Isis or Octalink.

After measuring the length of the axis (square only) you have all the necessary information to find the compatible box.

Isolated case: the "Howitzer" type box

Recently released, this box is only compatible with Truvativ Ruktion, Hussefelt and Holzfeller crankset.

Hollow shafts such as "external bearings" type

This type of housing is easily identifiable because the bearings are located outside the frame.

99% of the frames that have this type of case have an English thread 34.7 mm x24 TPI (also called BSA, BSC or Euro BB in the BMX world) the right bowl is screwed counterclockwise and the left bowl clockwise.

You will need a specific tool to remove the bottom bracket clamping screw and a housing disassembly with external bearings..

There are 4 main families of external bearing housings and it is here that the characteristics of the frame and pedal unit that we wish to associate with it must be clearly identified.

Tuto: How to change your external bottom bracket bearings?

Hollowtech II

This is the most common standard, the crankset has a 24 mm hollow axle attached to the right crank handle. The RaceFace x-type, FSA Mega-Exo and 24mm Rotor crankset have the same characteristics and will therefore be compatible.

On the road frames the bottom bracket is 68 mm wide and on the mountain bike frames there are 68 and 73 mm boxes.

Warning: the boxes given for 68mm (road) are only compatible with 68mm frames.

Hollowtech II 83 mm

The radicalization of certain "Gravity" practices has pushed manufacturers to widen their bottom bracket housings to increase lateral rigidity.

There are now specific boxes for 83 mm wide frames (e. g. shimano saint 83 mm).

Campagnolo

Campagnolo has developed 2 axes with specific characteristics: Ultra torque and Power Torque, the axis is 25mm in diameter and each standard has its own specific housing: the Ultra Torque crankset only fits on Ultra Torque housings, the same goes for the Power Torque.

Not Italian

Unlike the English step, the bowls are screwed counter-clockwise on the left side and clockwise on the right side. The thread measures 36 mm 24 TPI. This type of threading is no longer very widespread, it is still found at Pinarello in some artisanal manufacturers.

We will also note the existence of French and Swiss threads (35 mm) but not being used for a long time, we will not dwell on them.

Sram/Truvativ GXP

Developed by the manufacturer Sram/Truvativ, this standard has the particularity of having a 24mm axis on the right side reduced to 22mm on the left. The thread is in accordance with the English standard BSA/BSC.

Hollow shafts such as "internal bearings" type

There is a lot of confusion around the BB30 standard and internal bearing housings, indeed manufacturers tend to use this term to characterize the bottom bracket axis only: BB30 = 30 mm axis with star socket. Since the launch of this standard by Cannondale in 2009, all frame manufacturers have continued to develop this standard, adding PF30, BBright, UBB30, 386 evo... It is therefore also necessary to pay attention to the length of the axle and the internal diameter of the bottom bracket, which vary according to the standards. The assembly and removal of the bearings requires the use of a specific bowl flusher and bowl press.

The standard BB30

Also called "true BB30" or "BB30 short axis" the BB30 type housing is easily identifiable by the absence of cups.

The left crank can be removed with a suitable hexagon wrench and the axle is attached to the right crank.

The bearings are mounted directly in the frame box and held by means of circlips. A circlip pliers will therefore be necessary for disassembly.

The standard PressFit 30

Very close to the BB30 standard, the PF30 housing has the same bearings, the same gearbox widths and the only difference is that the bearings are mounted in troughs before being mounted in the frame. This increases the internal diameter of the bottom bracket to 46mm. Developed by Sram, this standard has been designed to facilitate the assembly and simplify the very demanding frame machining of the BB30.

The standard BBright Direct Fit

Nowadays used exclusively on frames Cervelo, this standard uses the same bearings and circlips as the BB30 but has a wider asymmetrical bottom bracket (11 mm offset on the opposite side of the bottom bracket). The BB30 bearings are therefore compatible, but care must be taken to use a long axle crankset.

The standard BBright Press Fit

Le BBright Pressfit est également utilisé par Cervelo uniquement à ce jour. Il exploite les mêmes roulements et cuvettes que le PF30 et présente aussi une boite de pédalier asymétrique plus large (11 mm de déport côté opposé pédalier).

The BB30 bearings are therefore compatible, but care must be taken to use a long axle crankset.

Note here the possibility of using adapters to mount pedals on a 24 mm axle.

The standard 386EVO

Developed by FSA, the 386EVO standard is a variant of the PressFit 30, it uses the same bearings and cups but is mounted on 86.5 mm wide boxes. It will therefore be necessary to use a crankset in the long axis. The advantage of this system is that it provides maximum rigidity. As for the PF30 and BBright Pressfit, it is possible to use adapters here to mount Shimano 24 mm or Sram GXP standard crankset.

The standard Pressfit Shimano

Shimano has not yet developed a 30 mm shaft to date but also offers a standard internal rolling housing. Also called BB86 or BB92, you have to be careful of these designations because there is a confusion between case width and shimano quality level. Indeed, this standard will adapt to all frames in 86.5 or 91.5 box width but we will find references such as bb71 or bb94 which correspond to quality levels (ultegra, xt, dura ace,...)

The standard Trek

Trek to launched its own standard in 2007. The BB90 and BB95 housings allow Shimano 24 mm or SRAM GXP standard pedals to be mounted. As for the BB30, the bearings are mounted directly in the frame (without cups) however they are not held by circlips but by shoulders in the frame box.


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