How to choose your MTB bottom bracket?

How to choose your MTB bottom bracket?

Visit MTB bottom bracket  The main purpose of the bottom bracket is to ensure the smoothest possible running of your crankset. This part must correspond to the standard of both the frame and the MTB crankset. Between frame and crankset standards, a little help is welcome!

Standards

  • Bearing quality: steel or ceramic
  • Crankset axle types: Hollowtech, GXP, BB30, etc.
  • Types of bottom bracket on frame: BSC, Press-Fit,...

Bottom bracket types

Let's start with the simplest: the bearing quality. Manufacturers generally offer the same housing model in two versions: one with steel bearings; the other with ceramic bearings. Ceramic has an unalterable, harder surface than steel. The advantages are low friction and long, maintenance-free service life. Please note that this only applies to 100% ceramic bearings, i.e. both balls and rings. The cost of the latter, however, reserves it for discerning practitioners.

As for compatibility with crankset axleDepending on the brand, there are different standards. To help you identify what you need, here's a list of the most common:

If the bottom bracket axle is part of the bottom bracket shell :

  • a Octalink 2nd version: cylindrical axle, 8 splines, 9 mm long.
  • b ISO square: 12.5 mm tapered square shaft at shaft end.

If the bottom bracket axle is part of the MTB cranksetalso known as a through axle :

Hollowtech II, X-type, Megaexo
24 mm diameter axle a.		 GXP
22 mm diameter left-hand axle b1,
24 mm right b2.		 BB30
30 mm diameter axle c. 
SRAM Dub
28.99 mm diameter axle c.		 PRAXIS M30
28 mm diameter axle, left e1,
30 mm right e2.

    It is also necessary to check the compatibility of the housing with the frame standard. MTB. Here are some more tips to get you started:

    • BSC (also known as BSA): the internal diameter of the frame is 34.8 mm.
    • Press-Fit: internal frame diameter 41 mm.
    • BB30: internal frame diameter 42 mm.
    • Press-Fit30: internal frame diameter 46 mm.

    REMINDER : Some BSC mountain bike frames use a bottom bracket extended to 83 mm (instead of 73 mm) and therefore require a specific bottom bracket axle.

    At Fat Bikesthere are 2 standard bottom bracket lengths: 100 mm (for 170 mm axle) and 120 mm (for 190 mm axle).

    Which bottom bracket should I choose?

    When it comes to replacing a bottom bracket, you won't necessarily have a choice apart from bearing quality. Your choice will depend on the standard of your frame and the axle of your bottom bracket.

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