Jack Dreyer | Thursday 13th July 2023 12:00pm
If you’ve made the leap to foot-powered transport and are getting stuck in with bike maintenance, you’ll likely have heard of a bicycle’s ‘bottom bracket’ – but what exactly is it, what does it do, and how can you keep it in top condition?
Let’s find out.
The bottom bracket is for pedals
While the name might indicate that it has something to do with where you sit, the bottom bracket is actually the bearing system that keeps your bike’s foot pedals locked in and turning in a regular, dependable way.
The frame on most modern bikes will usually be a welded central body that’s in a vaguely diamond shape. This is the solid bit that everything else gets attached to. This solidness helps to maintain and distribute all the stresses of the bike so that your wheels turn properly, you can steer your handlebars easily, and you can pedal effectively.
And here’s the most important thing: because the bike is entirely powered by the force of your pedalling, if there’s play in the pedals then you get a significantly reduced amount of force being transferred to the wheels, the potential to damage parts of your bike like the gears, or even to get injuries in your feet or ankles. If you’ve ever ridden a bike with front suspension, you’ll know how much more effort it takes to accelerate quickly – because the suspension cushions your forward force.
A bottom bracket helps stop this from happening through wiggle in the pedals.
How a bottom bracket works
The frame of the bike is usually made with a hole through it for the bottom bracket to sit in. They’re usually held in place either with a threaded connection or through a pressure-fit mechanism and they then let the pedal (or ‘crank’) spindle pass through and lock in.
In this way, the spindle is able to turn freely within the bearings while the bearings are held sturdily to the bike. Importantly, the thread is usually the opposite direction of the pedal force – so that as you’re pedalling the bike you never accidentally unthread the pedals.
How to tell which bottom bracket your bike has
This seems like it’d be an easy answer but there’s no real standardised design for bottom brackets – they’re one of the components where essentially every bike manufacturer has a different design. They all work in much the same ways, and some are compatible with certain standardised tools, but often you’ll have to consult your bike manufacturer’s guidance on what your bottom bracket is and how to get the tools to remove it.
When do you need to replace a bottom bracket?
Like with any components that have to withstand a lot of force, the ball bearings in the bottom bracket mechanism eventually wear down and don’t turn as efficiently. As they wear down, they don’t maintain a good connection between the inner and outer rings of the bearing – so they end up slipping. This is actually what makes older washing machines so loud; the broken bearings cause the drum to keep banging against the case while it’s spinning.
You usually need to remove bottom brackets if you need to replace them or, in some cases, in order to top up the grease within the spindle casing.
Need an expert?
A big issue with lots of bike maintenance is that the lack of standardisation means you often need to get specific tools for specific bikes. If looking after your bottom bracket feels daunting – we’ve partnered with bike specialists, Fettle, to deliver bike maintenance services at your local Kwik Fit centre.
Any facts, figures and prices shown in our blog articles are correct at time of publication.
Wednesday 22nd November 2023
It can be hard to tell if your puncture can be repaired or not. Read our handy guide to understand if your tyre can be saved or if you need a replacement.
Wednesday 18th October 2023
Driving on old or worn tyres can be dangerous so you need to maintain them properly. Read about how long tyres should last and how to know if your tyres are old.
Thursday 27th October 2022
Driving in the rain isn’t only a pain but can be surprisingly hazardous – here are our top tips for staying safe in wet & icy weather this winter.