GXP: External Bottom Bracket. GXP is different — and better. Other systems rely on side-loaded bearings to eliminate play, causing bearing wear. GXP captures the left-side bearing between the spindle and the left crankarm and allows the drive-side bearing to float axially on the spindle.
What is a bb30?
The term PF46 refers to a frame shell bore of 46mm. The term PF30 is an early industry name used to distinguish this standard from the previous BB30 (PF42) standard. The frame shell has a smooth bore with an approximately 46mm inside diameter. The shell widths are 68mm for road bikes and 73mm for mountain bikes.
How do I know which bottom bracket I need?
To find out the size of bottom bracket needed, measure the inside of the bottom bracket shell in your frame, it will be 73mm, 70mm or 68mm. Some older frames may have Italian threaded bottom brackets, instead of the more modern English.