Types of MTB Bottom Brackets & How to Choose One

Your bottom bracket takes a huge amount of punishment on every ride, connecting the frame and crankset while handling the constant pressure of pedalling. When the bearings become worn or the bottom bracket is poorly matched to your setup, you may notice creaking, grinding, stiffness or unwanted movement. Choosing the right replacement starts with understanding your frame and crankset.

Threaded Bottom Brackets

Threaded bottom brackets screw directly into a threaded bottom bracket shell in the frame. BSA is one of the most common standards found on mountain bikes, and this type of bottom bracket is generally straightforward to remove and replace.

For riders using a 24mm axle crankset, a compatible threaded bottom bracket provides a reliable option for maintaining smooth crank rotation. It's important to check both your frame's shell and crankset specifications before ordering a replacement.

Press-Fit Bottom Brackets

Press-fit bottom brackets are installed directly into the frame rather than being screwed into place. BB30 is one example of a press-fit standard and is designed around a 30mm axle crankset. Because different press-fit systems can have different dimensions, always check your frame's specific bottom bracket standard before purchasing replacement bearings or a complete bottom bracket.

Square Taper Bottom Brackets

Square taper bottom brackets are an older but still widely used standard, and Middleburn manufactures cranks specifically designed for this type. The RO1 SQ and RS7 SQ models are both square taper compatible and fit in the same frame shells as HT2 type bottom brackets. Unlike outboard systems, square taper bottom brackets come with a given axle length, typically ranging from 107mm up to 130mm, with adjustable axle designs also available. When fitting cranks to a square taper bottom bracket, always follow the bottom bracket manufacturer's recommended settings for tightening torque and positioning.

How Do You Choose the Right Bottom Bracket?

The most important factors are your frame's bottom bracket standard and crankset axle diameter. For example, a 24mm axle crankset requires a compatible 24mm bottom bracket, while BB30 systems require the appropriate BB30 components, and square taper cranks require a correctly sized square taper bottom bracket with the right axle length for your frame. You should also consider bearing quality, particularly if you regularly ride in wet or muddy conditions. Worn bearings can affect drivetrain efficiency and create unwanted noise, so replacing them when necessary keeps your bike running smoothly.

If you're upgrading rather than simply replacing a worn component, ceramic bearings can also be an option. Ceramic bearing kits can reduce friction and offer longer bearing life compared with standard steel bearings.

Bottom Brackets from BETD

At BETD, our bottom bracket range covers key setups for road, mountain bike and gravel builds. Our Middleburn HT2 X-Type Bottom Bracket is compatible with any 24mm axle crankset, as well as Enduro ceramic bearing kits for HT2 and BB30 applications. Shop the full range online today to find the right replacement for your drivetrain, or speak to our experts for help and advice.