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How do I know what size bottom bracket I need?

How do I know what size 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.

What do bottom bracket sizes mean?

The 68mm and 73mm dimension measure the width of the bottom bracket on the frame of the bike with no BB installed, simply the width of the shell. Most road bikes that use a threaded bottom bracket measure 68mm wide and most cross country/trail mountain bikes measure 73mm.

What does BSA bottom bracket mean?

In terms of the BSA we often see associated with bicycles, specifically bottom brackets, it originates from the Birmingham Small Arms company. These days, BSA, ISO, and English are used interchangeably to refer to what is now considered to be a standard threaded bottom bracket shell or bottom bracket.

Are all bottom brackets 68mm?

There are 4 widths available with BSA bottom brackets; 68mm, 73mm, 83mm or 100mm. For road bikes, a BSA bottom bracket is always 68 mm wide. Other sizes, and particularly the 73 mm width, is commonplace with mountain bikes. The 83 mm and 100 mm dimensions have become rare these days.

Are bottom brackets all the same size?

Is BSA same as ISO?

This standard also goes by other names, but they all mean the same thing. These are: BSA, BSC, BC, ISO, British, and Euro, the name used in BMX bike circles. The term BSA stands for Birmingham Small Arms, a British company that produced bicycles, cars and other durable goods.

What is BSA and BB30?

BB30 specifically refers to a standard that used 68 or 73mm shells with a 42mm inner diameter meant to press 6806 bearings directly into the frame which had a 30mm internal diameter. Most outboard bottom brackets for BSA threaded frames originally were designed around cranks with a 24mm spindle.

Are all bottom bracket shells the same diameter?

Threaded bottom brackets shells have been made over time in various thread standards that are not interchangeable. The common threaded bottom bracket uses cups or adaptors with the thread specification of 1.37″ x 24 threads per inch (approximately 34.8mm diameter).

What are the different sizes of bottom brackets?

The two major dimensions that differentiate bottom brackets of similar types are the shell width and spindle diameter. Hopefully, we can help clarify some of the more common bottom bracket sizes so that upgrading your cranks can be a simpler process.

How do I determine the bottom bracket standard in my frame?

To accurately determine the bottom bracket standard in your frame, it is best that you remove your crankset, and any installed bottom bracket cups or bearings. Then measure both the inner diameter and width of your frame’s bottom bracket shell. The chart below lists most of the current bottom bracket standards found on today’s frames.

What size spindles do I need for my brackets?

“3” series spindles normally fit 68 mm ISO/British/French bottom brackets. “5” series spindles normally fit 70 mm Italian bottom brackets, also 68 mm French with thin cups.

What is the difference between 68/73 and 83mm bottom brackets?

The 83mm English threaded bottom bracket uses the same design as the 68/73mm system but measures 83mm wide. This is most usually seen on downhill mountain bikes in order to maintain the most efficient chainline. BB92 is a shell type that is quite common on high end mountain bikes of many brands.

Posted in Advice