Drivetrain
What is a Bottom Bracket?
The bearing set the cranks spin on, hidden inside the frame.
Simplified schematic — not to scale.
In plain English
The bottom bracket is a sealed bearing unit that sits inside the frame's shell, letting the crankset spin freely while carrying your full pedalling force.
A simple analogy
“It's the hidden hinge that lets a very stiff frame and a spinning crank get along.”
How it works
Bearings inside the unit let the crank axle rotate with minimal friction, while sealed covers keep water and grit out of the moving parts.
Signs of trouble
- ⚠Creaking noise when pedalling hard, especially out of the saddle
- ⚠Play when you rock the crank arm side to side
- ⚠Gritty feeling when spinning the cranks by hand
Rough UK cost
£20 – £90 for the part, plus fitting
Always get a written quote. Prices vary by bike, region and parts brand.
Heads up: Bikeautonomy is for general guidance only. If your bike is behaving oddly or you're not confident, get it looked at by a qualified bike mechanic.