What is a 73mm bottom bracket?

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.

Can I use a 68mm bottom bracket in a 73mm shell?

You could install it, but it will shift your chainline, shift the centerline of your feet, clearance issues might arise on the non-drive side, and you might be leaving some BB shell threads exposed on the non-drive side as well.

How many spacers does a 73mm bottom bracket have?

one 2.5mm spacer
If your bottom bracket shell is 73mm wide, you only need one 2.5mm spacer fitted to the drive side.

What is an English thread bottom bracket?

The common threading for bottom bracket shells is called “English.” The left-side cup is a right-hand thread direction, which tightens clockwise and removes counterclockwise. The right-side (drive-side) thread is a left-hand thread, which tightens counterclockwise and loosen clockwise.

Are all bottom brackets 68mm?

On road bikes, it’s always 68mm. With mountain bikes, 68mm is most common too, but sometimes the wider version with 73mm width can be found. The diameter of the bottom bracket is 41.96mm, and the bottom bracket bearings are always pressed into the frame separately.

How do I know my bottom bracket size?

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.

How do I know what size bottom bracket I need?

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).

How do I know what size bottom bracket to buy?

How do I know if my bottom bracket is English or Italian?

The key difference is in how the two thread into the bottom bracket shell. Like pedals, one side of a BSA standard bottom bracket shell is reverse (left) threaded, while both sides of an Italian standard bottom bracket shell are regularly (right) threaded.

When a bottom bracket size is listed as 1.37 x24 What does the 1.37 measurement refer to?

The bearings denote: 1.37 * 24. This means that the diameter of the thread is 1.37 inch and that it turns 24 times per inch. The diameter of a BSA bracket is between 33.6 and 33.9 mm.