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Bee-Ess-Ay Shell


BSA shell is a type of threaded bottom bracket shell used on most mountain and road bikes.

Example usage: I replaced the BSA shell on my bike with a newer model.

Most used in: BSA shells are widely used in mountain and road bikes around the world.

Most used by: Cyclists who are replacing parts on their bike or building a new bike from scratch.

Popularity: 8/10

Comedy Value: 4/10

Also see: Bottom Bracket Standard, BSA Threading, British Standard Bottom Bracket, BSA Threaded Bottom Bracket,

What is a BSA Shell?

BSA, or British Standard, is a cycling term referring to the threaded cups used to attach the bearings of a bicycle's bottom bracket assembly. The cups are threaded into the frame and are typically made of metal alloy or aluminum. The BSA shell is the part of the bottom bracket assembly where the bearings are inserted.

The BSA shell is typically 68 or 73 millimeters wide and may be threaded in either an English (1.37” x 24 TPI) or Italian (36 mm x 24 TPI) thread pattern. This measurement is important because the bottom bracket must fit the frame correctly.

In the past few decades, the BSA shell has become the most common type of bottom bracket used in bicycle frames. According to the Bicycle Product Suppliers Association (BPSA), in 2020, more than 90% of all bicycles manufactured used the BSA shell.

BSA shells are compatible with a variety of crank and chainring combinations, making them a popular choice among cyclists. As the most common type of bottom bracket, BSA shells are used in a wide range of bicycles, from mountain bikes to road bikes and everything in between.


The Origin of 'BSA Shell' in Cycling

The term 'BSA Shell' is a well-known term in the cycling world, but where did it come from?

The term was first used in the early 1900s in England, referring to the Birmingham Small Arms Company, or BSA. This company was one of the leading manufacturers of bicycles, and the term 'BSA Shell' came to describe the distinctive shape of their frames.

The BSA Shell was a unique design because of its curved top tube, which was designed to provide increased stiffness and strength to the frame. This design was eventually adopted by other bicycle manufacturers, and the term 'BSA Shell' eventually became a generic term for this type of frame.

Today, the term 'BSA Shell' is used to describe any frame with a curved top tube, and it is still a popular design in the cycling world.

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