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The bottom bracket on an XC mountain bike performs several essential functions. Here are its main characteristics and standards:

Function :

1. Bottom bracket support:

The bottom bracket houses the bottom bracket spindle on which the cranks are mounted. It ensures the proper alignment and smooth operation of the bike's drivetrain assembly.

2. Transmission of pedaling power:

The bottom bracket allows for the efficient transmission of the rider's pedaling power from the cranks to the chain, helping to propel the bike forward.

3. Protection from the elements:

It protects the bearings and internal components of the bottom bracket system from water, dirt, dust and other debris that could negatively affect their performance and durability.

Features :

1. Housing type:

There are several types of bottom brackets, each with different fitment and compatibility specifications. The most common types are press-fit housings, threaded housings (English or Italian), and press-fit housings.

2. Width:

Bottom bracket width may vary depending on bike type and frame design. The most common width standards for XC mountain bikes are 68mm to 73mm wide housings for threaded housings and press-fit housings.

3. Threading or fitting:

The threaded housings are screwed into the frame and held in place by a corresponding thread in the frame. Press-fit housings are pressed into the frame without threads and held in place by pressure. Press-fit housings use a similar method, but are designed for precise press-fit into the frame without additional pressure.

4. Type of bearings:

Bottom brackets can use different types of bearings, such as external bearings, internal bearings, or sealed cartridge bearings. These choices affect the durability, ease of maintenance and performance of the bottom bracket system.

5. Construction material:

Bottom brackets are typically made from aluminum, steel, or reinforced plastic for the optimal combination of lightness, strength, and durability.

In summary, the bottom bracket on an XC mountain bike is an essential component that ensures the proper functioning of the bike's transmission and pedaling system. With different features and standards available, it is important to choose a bottom bracket that matches the frame design, crank type and specific needs of the XC mountain bike.