MTB Bottom Brackets

What is an MTB bottom bracket and what is its main purpose?

The bottom bracket sits in the frame shell and supports the crank spindle. It must absorb enormous axial and radial forces, especially during landings. A good bearing runs silky smooth and is sealed against dirt and water.

What frame standards are there?

BSA / Euro BB (Threaded)

The absolute standard for Dirt Jump frames (e.g., NS Bikes, Canyon, Rose). The bearing cups are screwed into the frame.
Important: The drive side has a left-hand thread (tightens counter-clockwise)!

Pressfit (BB86 / BB92 / BB30)

The bearing cups are pressed directly into the frame. More common on carbon frames or in racing. Requires a press tool.

Which bearing do I need for my crank?

The inner diameter of the bearing must exactly match your crank axle:

How do I install a BSA bottom bracket?

1. Clean the threads in the frame and grease them generously.
2. Check the spacer instructions for the crank (usually depends on shell width 68mm or 73mm).
3. Screw the cup marked "R" (Drive Side) into the drive side (Left-hand thread! Turn left to tighten).
4. Screw the cup "L" (Non-Drive Side) into the other side (Right-hand thread).
5. Tighten both sides with the appropriate bottom bracket tool.

How do I detect wear?

• Creaking: Often a sign of dry threads or defective bearings. Removing, cleaning, and regreasing often helps.
• Play: If you can wiggle the crank arms sideways, the bearings are worn out and must be replaced.
• Rough feeling: If the crank turns "gritty", dirt has entered inside.

What do the specifications mean?