How to Measure a Bottom Bracket

Last Updated on November 24, 2020
written by Cycle expert Alex Bristol
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The bottom bracket is usually located where the down tubes of the frame joins with the seat. It contains two bearings which are placed in such a way that they allow the pedals and the chain rings to rotate freely. The good thing about bottom brackets is that most of them are made of top quality materials which allows them to last for many years.  However, they come with different design which are suitable for different types of bikes. In this article, we shall guide you on the steps you should follow when measuring the bottom bracket.

Required items

  • Metric ruler – You can use either a metric ruler or a caliper to measure the external and internal dimensions.
  • Spindle – This one is an axle where the pedal rotates.

Procedure

  1. Preparation

You need to check the spindle component of your bottom bracket frequently. When doing this, you need to know the exact measurements of the two parts.  You should take the measurements of the bottom bracket in mm. This means that you will need a caliper or a set of metric ruler.

  1. Taking the measurements of the shell

If you want to take accurate measurements of the bottom bracket shell, you should flip the bike upside down then hold the ruler or calipers against the casing. When measuring, you should determine the length of the shell from one end of the shell to the other. Don’t include the length of the spindle located in the shell. Most of the bottom bracket shells have a length of 68, 70 and 73 millimeters.

  • Measure the bottom bracket spindle

To know how you can take the measurements of the bottom bracket spindle, you need to first get rid of the cranks arms. Once you have removed them, you can now determine the length of the spindle from one end to the other. Remember to also take the measurements in millimeters. However, in case the cranks of your bike are connected by nuts instead of bolts, you should not consider the connected parts of your spindle when taking the measurements.

In case you are not sure the best bottom bracket you should purchase, you need to be conversant with following terms;

  • Spindle diameter– Most of the bottom brackets have a spindle diameter of 19mm, 24mm and 22mm.
  • Bottom bracket shell – These ones are the most common types; MID, USA, Euro and SPANISH. Each name represents the size of the bearings which are only compatible with specific frame sizes.
  • Bearing version– SB represents sealed bearings while BB represents ball bearings.

Conclusion

When taking the measurements of the bottom bracket, you need to be aware that it has two parts. The first part contains the frame and is usually known as the bottom bracket shell. The other part goes inside of the shell and is usually referred to as the bottom bracket or the spindle. During installation, you need to take the correct measurements of the bottom bracket because it will help you to determine whether you are installing the correct size.  Remember the size of the bottom bracket may also vary depending on the type of your bike.

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