What size of bottom bracket do I need for my bike?

Last Updated on July 27, 2020

This guide has been written by cycling review expert Alex Bristol

Last Updated on July 27, 2020

If you have been planning to upgrade the cranks on your road bike or mountain bike, you need to look for a compatible bottom bracket that matches the type of your bike. This means that you have to think of the size since bottom brackets are available in different sizes. The common dimensions that differentiate these units are the spindle diameter and the shell width. Below are some of the common bottom bracket variations.

English Threaded

English threaded BB are the oldest or the longest standing bottom brackets. They were replaced by carbon-threaded brackets but they are still relevant even today. The bearing threads are attached directly on the frame  but the bearings remains outside. One of the major advantages of these units is that they provide a secure fit as compared to the pressftit bottom brackets. Again, they are very easy to install because you will only need to use a special wrench when removing.

English Threaded 83 mm

 These ones have a similar design as the 68/73mm but they have a width of 83mm. They are very common in downhill mountain bike and they are very effective in maintenance of an efficient chain line.

BB92

BB92 are usually used in high-end mountain bikes. Sometimes they are referred to as Shimano press fit GXP. Unlike other types, these ones comes with a metal or a nylon shell  and they have a width of 92mm. They are very reliable but are not the best for muddy areas.

PF30 and BB30

These ones work well with cranks that have a 30 mm spindle. However, they are also compatible with 24 mm spindles though you will need to use an adapter. The bearings of BB30 press directly onto the frame. You can use a removable clip to keep them in place. They are very common in most road bikes and the good thing about them is that they are very light.

On the other hand, PF30 bottom brackets secure the bearings in the metal or nylon shell which is then pressed onto the frame. You can easily find them in mountain bikes though they are not as popular as the BB92.

Specialty

Many fat bikes and road bikes only works with specialty sizes. For example, you will find that some fat bikes normally use a shell that has a width of 121mm or 131mm.

How to determine the correct crank set

 The crank length is determined by measuring the centre of your BB axle to the centre of the axle pedal. Most of the bikes use a crank size of 170mm or 175mm. The shortest ones have a crank length of 140mm while the longest have a measurement of 190mm.  You should select crank arms that matches the measurements of the inside leg if you want to be comfortable.

Conclusion

Unlike other parts of the bike, bottom brackets may be a bit difficult to understand. However, we have tried to simplify various things you may need to know so that it will be easier for you when buying.

Sources:

1. Where is the Bottom Bracket on a bicycle? – Post by Evans cycles

Related Post: 10 Best Bottom Brackets [Review]

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