How to Measure Bottom Bracket – The Practical Steps

Are you one of those people who are searching to update the cranks on your bike? Or you just wish to replace the bottom bracket? But, do you know how to measure bottom bracket? Well, you need to bear in mind that it is crucial to ensure you get the proper bracket for the work.

Along with a lot of standard sizes available in the market today, this may seem overly complicated, and this is the main reason why this article is here.

What is a Bottom Bracket?

Your bottom bracket is found at the intersection of the seat and the down tubes of your frame. It has two bearings; the first one located at any side through that the pedal hinge is suited, allowing the chainrings and pedals to turn freely. Its assembly might as well includes lock rings and spacers depending on design and type.

Having a high-quality bottom bracket, adequately installed must work for you with long years of hassle-free riding; however, bearings could wear out, or the bottom bracket can become unfastened. This can result in excess movement or annoying noises in the bottom bracket that can ruin your frame, which is the reason why it is why it is best to ensure that the bottom bracket is in decent condition or secured.

How to Know Which Bottom Bracket is Suitable for Your Needs?

Many people are not aware of how to pick the right bottom bracket that suits their needs. To some level, the kind of a bottom bracket you prefer will be identified by the frame type, since some frames – especially carbon models beyond a particular price point – are created to utilize a form of bottom bracket and one kind only.

Along with some bottom bracket types, having perished totally, you will find three crucial designs remaining, including:

  • Press-Fit bottom bracket
  • Outboard bottom bracket or External
  • Cartridge-Type bottom bracket

Cheap, well-sealed and easy-to-fit cartridge bottom brackets are discovered on many road bike frames and mountain bike frames at a more affordable, with external bottom brackets at a point having generally changed them on the higher-end models.

A bicycle Bottom Bracket

No matter what type you pick, or grateful to stick into, you need to ensure you pick the right width to fit the bottom bracket shell. Those usually are 68 or 73 millimeters on mountain bikes even though again, this is not such a consideration with press-fit bottom bracket.

Kinds of Bottom Bracket

1. Press Fit bottom brackets

Did you know that press-fit bottom brackets are seen on the increasing amount of mid to high-end carbon fiber of road bikes and mountain bikes, and a few of aluminum models? With such, the bearings are pressed straight into the frame, either into races or in aluminum cups, which are molded into the structure of its frame.

The primary advantage of this type of bottom bracket is that it enables a broader bottom bracket shells devoid of affecting axle width. Therefore, allowing larger tube sizes to be utilized and growing frame difficulty in the bottom bracket area.

In turn, this enhances the power transfer between frame and rider by decreasing flex at the bottom bracket. Nevertheless, you will find lots of iterations and sizes according to the manufacturer – PF86/92, BB90, PF30, BB30 to name but a few.

2. External bottom brackets

On the other hand, external bottom bracket is where the cartridge bearings lie in aluminum cups that are on the outside of the bottom bracket shell. The concept behind this is that it enables the need of a bigger diameter axle for enhanced rigidity in the bottom bracket area and thus increased transfer.

Moreover, the external bottom bracket setup denotes greater toughness for a lesser weight; however, it could have disadvantages. Do you know that bearings could die faster if they are not properly aligned? It is most of the time suggested to let the bottom bracket shell faced for maximum durability.

Ceramic bearings are famous and smoother running and long lasting compared to the standard steel ones.

3. Cartridge Type bottom brackets

Lastly, cartridge bottom bracket is an older standard that features a small diameter internal and axle bearings sealed in a metal cylinder that screws into the bottom bracket shell as a single unit. While the predecessors of this design obliged precise bearing adjustment with the use of two spanners, cartridge bottom brackets became famous as “fit and forget solution”.

After they wore out, you merely changed them, instead of fiddling around bearings.

How to Measure Bottom Bracket?

Now that you are familiar with the types and which bottom bracket is suitable for your needs. After that, you should be ready to know the fantastic ways on how to measure bottom bracket.

Items Needed

Of course, when we talk about measuring, you need a tool that will help you estimate the bottom bracket precisely and correctly. Some of the objects which are needed throughout the process are the following:

  • Metric rulers or calipers. This is an instrument for measuring internal or external dimensions, having two hinged legs resembling a pair of compasses as well as out-turned or in-turned points.
  • Spindle. Spindle is an axle around that a pedal rotates, strung at one end to screw to crank arms

Steps to Follow

1. Preparation

Keep in mind that the spindle component of the bottom bracket of your bike frequently needs to be changed, in which case you will require a precise measurement of both parts.

Additionally, the bottom bracket is measured in mm, thus you will require a set of metric ruler or calipers.

2. Measuring the shell of bottom bracket

For you to know how to measure bottom brackets shell on your bike frame, flip the bike upside-down and hold your calipers or ruler against the casing. Then, you should make sure to measure the length of your shell from one end to another, not including the length of your spindle located inside the shell.

The majority of bottom bracket shells measure 73, 70 or 68 millimeters long.

Bottom bracket tool

3. Measuring the bottom bracket spindle

Meanwhile, to know how to measure bottom bracket spindle, make sure to get rid of the crank arms. When the crank arms are detached, measure the length of your spindle from one end to another in millimeters.

However, if the cranks on your bike connect with nuts rather than of bolts, do not include the connected parts of the spindle on the measurement.

For more information about bottom brackets, watch this:

Bicycle bottom bracket, headset bearings, bearing cups and spindle

Final Thoughts

To sum up, after reading this guide, you have got some ideas that the process of how to measure bottom brackets are quite a complicated concept. If your concerns are answered here, then it is great! You can now get yourself some new bike parts.

Watch this video to learn how to change and replace the bottom bracket:

Do you still have issues in mind that you want to talk about? Feel free to comment below! Please share this guide if you find this helpful. You will surely help more people who have the same issues like you.

Lauren Anderson
 

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