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What is a bottom bracket?

Where is it located?

Your bottom bracket is housed within the bottom bracket shell of your frame, in between your

crankset. However, depending on the bottom bracket system you have installed the bearings

themselves will either sit inside your frame or externally.

There are several bottom bracket options on the market, so lets take a look at the 3 most

common variants.


External


These bearings are housed within cups which are either threaded or pressed into the

bottom bracket shell.

In this example we are looking at threaded bearing cups.


This is how these bearings look outside the frame . Often the cups are separated  by a plastic

sleeve which helps to prevent water ingress.

We advice to replace this system every 3000 miles and to have them inspected and cleaned

every 6 months to reduce clicking noise. If there is any freeplay or grinding, we suggest they’re

replaced as soon as possible.



BB30


BB30 is a very common choice for frame manufacturers, as the bearings

sit directly within the frame providing great lateral stiffness.

The bearings are pressed into the bottom bracket shell and are butted against

steel circlips on their inside face. This metal against metal setup however is often the cause

of the common BB30 bottom bracket clicking sound.

“Don’t worry folks it’s usually not your expensive carbon frame breaking apart.” :)



This is how your BB30 bearings look outside of your frame accompanied by their circlips.

This bearing system requires a little more care and maintenance. As such, we advise

them to be replaced every 3000 miles and to be inspected and re-greased every 6 months.

However, should any clicking sounds appear we recommend you have them inspected

as  soon as possible.


Square taper


This bottom bracket can be considered the ‘classic’  system. While not

viewed to be high performance it is often more durable than other

bottom brackets. Square taper offers several axle length options

which is very useful when undertaking customisation projects.

The bearings are housed in a unit which is threaded into the BB shell.


This is how the square taper unit appears outside of your frame. We recommend replacing

this bottom bracket every 6000 miles and to be inspected and cleaned every 12 months.

As with the other systems, if you notice any freeplay or grinding we recommend you replace

the unit as soon as possible.

These guidelines are based on the high quality shimano sealed units, unit integrity may

differ  by brand.


A bottom bracket is quite simply a housing system for

bearings to facilitate rotational drive.