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How do I determine bottom bracket size

5 min read

Asked by: Stacey Thomsen

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 is the most common bottom bracket size?

The common threaded bottom bracket uses cups or adapters with the thread specification of 1.37″ x 24 threads per inch (approximately 34.8mm diameter). The most commonly used term for this standard is “English” threading, sometimes abbreviated as ENG.

Are there different sizes of bottom brackets?

There are 4 widths available with BSA bottom brackets; 68mm, 73mm, 83mm or 100mm. This bottom bracket clearly shows you on the outside what bearings have been fitted to the bike. 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.

Will any bottom bracket fit my bike?

To know the size of Bottom Bracket that you require, simply measure the length of the inside of your Bottom Bracket shell. It’s usually 73mm or 68mm on all modern bicycles. Older bicycles may have the less conventional Italian threaded Bottom Brackets, unlike the more modern English Threaded Bottom Brackets.

What do numbers on bottom bracket mean?

The numbers ranging from 86 to 132 refer to the nominal width of the shell in millimeters, which is not related to the press fit of the bearings. These bottom brackets will vary in the width of the dust sleeve used for that different widths.

Is BB92 the same as PF92?

The frame’s bottom bracket shell inner diameter is 37mm. A bearing with an OD of 37mm is pressed directly into the frame. Trek is moving away from the BB90/95 system to what they call PF92, which is the same as a BB92 (41mm ID shell and 92mm width).

What is a 68 73 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.

Do I need to grease the bottom bracket?

In the case of the bottom bracket, you will use the grease when you install it, whether it is threaded, press fit or similar, and in the same way when you install or clean the cranks. The point of contact of the cranks with the bottom bracket should be greased too.

How many types of bottom brackets are there?

two main

There are two main types of bottom bracket design, one with a threaded shell which the bearings screw into, or a press-fit design which the bearings press into the shell. Bottom brackets are largely distinguished by the shell and axle width and the diameter of the shell and axle.

Does changing bottom bracket make a difference?

(Click here to read BikeRadar’s complete guide to bottom brackets.) According to Friction Facts’ latest report: “No statistically significant difference exists showing a general advantage or disadvantage of a standard type under similar loading conditions.

Do all cranks fit all bottom brackets?

In general terms, most cranksets can be fitted to a variety of bottom bracket shells, though much of this compatibility depends upon the availability of suitable hardware (see next section). Any incompatibilities that do arise are often related to the length and/or diameter of the crank axle.

What is the difference between BB92 and BB86?

BB86 vs BB92? No difference. They are one and the same bottom bracket. Well, BB86 refers to road bikes with their 68mm BB shell; BB92 refers to mountain bikes with their 73mm BB shells.

What spindle length do I need?

How to measure a bike bottom bracket

Are all bottom brackets the same?

However there are many different sizes and iterations according to manufacturer – BB30, PF30, BB90 ,PF86/92 to name but a few – and not all are interchangeable.

What are the different types of bottom bracket?

There are two main types of bottom bracket design, one with a threaded shell which the bearings screw into, or a press-fit design which the bearings press into the shell.

How do you measure a bottom bracket on a bike?


Quote from video: In there so frame to frame. And you just want to measure that you're going for the metric. So you can see this is 73. That is 73 millimeters. So usually you're gonna have a 68.

Do bottom brackets make a difference?

(Click here to read BikeRadar’s complete guide to bottom brackets.) According to Friction Facts’ latest report: “No statistically significant difference exists showing a general advantage or disadvantage of a standard type under similar loading conditions.

Do I need to grease the bottom bracket?

In the case of the bottom bracket, you will use the grease when you install it, whether it is threaded, press fit or similar, and in the same way when you install or clean the cranks. The point of contact of the cranks with the bottom bracket should be greased too.

How do I know what size crankset to buy?

How to measure crank length? Crank length is measured from the centre of the bottom bracket axle to the centre of the pedal axle. If you’re not sure what length the cranks on your bike are, the quickest way of finding out is typically to just look at the backside of your cranks, just below the pedal axle.