Bottom Bracket On Bike: How To Choose The Best Type?

Getting into the cycling game involves knowledge about many sections, like techniques, models, and mechanics. For this reason, you must understand a small but crucial part of the bike, the bottom racket. So, what is a bottom bracket on bike, and what is its function? Let’s check!

What Is Bottom Bracket On Bike?

The bottom bracket serves as a joint to secure the connection of a crankset to the bike’s frame. Without the bottom bracket, unwanted friction will occur between the crankset and the bike’s frame. 

Typically, every bike consists of a shell covering the bottom bracket, and bike manufacturers will press or thread the bottom bracket into the shell. 

This bracket can reach and be firmly attached to the front triangle frame through the shell. Therefore, it’s not an exaggeration to affirm that a bike won’t be able to rotate properly without relying on the bottom bracket.

bottom bracket on bike

However, the bottom bracket of bicycle can’t be responsible for a bike’s smooth rotation by itself. It must accompany another accessory called a bearing. 

In the past, bikers could modify or repair the bearing in case of damage or malfunction. But now, bearings are upgraded, and bikers are recommended to replace the damaged one with a new one. 

How Many Standard Types Of Bottom Bracket On Bike

If you are a stranger to the biking world, you will get overwhelmed by the number of bottom-bracket variants on the market. No matter how many kinds there are, these standard types will meet your demand. 

#1 Threaded Bottom Bracket

The threaded bottom bracket is held into the drive side of the frame, including the spindle and the sealed bearings. Around the spindle, there’s a cartridge container covering the sealed bearings and a crank mounted to the tapered axle. 

Honestly, this type is losing its popularity to the more upgraded bottom bracket types. The reason may lie in the challenging installation of the crank. To attach a crank to the threaded bottom bracket or detach it, you must opt for a bulky Allen key or Hex key.

#2 External Threaded Bottom Bracket

In this case, the bottom bracket features a hollow core, so it must be threaded into the frame via two cups on the outside of both lateral holes. The externally placed cups allow bikers to apply more durable bearings and more secure spindles for the unused area. 

what is bottom bracket on bike

For this reason, the bottom bracket doesn’t need to connect to the spindle. On the other hand, manufacturers will put the crank through the hollow body of the bracket and fuse the spindle into the crank.

Nowadays, modern bikes likely have an external threaded bottom bracket. When you go for this type, the only notice is to check for compatibility between the bracket with the frame and the cranks.

#3 Pressed Bottom Bracket

Although the lateral threaded bottom bracket is used on modern bikes, it is not a decent choice for high-end carbon fiber products. Therefore, the manufacturers came up with a solution named pressed bottom bracket. 

In 2000, the first threadless bottom bracket was introduced to the public. Bike makers will press the bottom bracket into the frame instead of threading it.

The advantage of pressed bottom brackets is that they will ensure proper large space for stiffer crank spindles. Of course, coming up with an innovative improvement also requires excellent making. 

When the pressed bottom bracket bike is perfectly manufactured and installed, you can rely on its utility. Or else, the creaking sound will ruin your experience with your expensive bikes. If you aren’t a pro at bike mechanics, don’t try installing this type of bracket yourself.

How To Choose A Bottom Bracket On Bike?

bottom bracket of bicycle

Firstly, you must detach the cranks from the frame to measure the bottom bracket shell. If the bike already has a bottom bracket, you must remove the existing one. 

Although some manufacturers include figures about this part on the bike frame, you shouldn’t entirely trust the numbers. 

Next, use a special measuring item to identify the width and diameter of the bottom bracket shell. You can find the item on the Internet. 

You can’t ignore the crankset spindle because it plays a considerable role in deciding where the bearings should be. There are various configurations of the spindle, and it’s impossible to figure out its diameter without appropriate calipers.

Two crank arms will be fused into both lateral sides of the spindle. You must identify the spindle’s length as well as the distance between the two arms. The gap must be measured precisely because this is where you install the bottom bracket and its shell.

After getting all the crucial dimensions, your task is to choose a bottom bracket fitting the figures. 

The Durability Of A Bottom Bracket On Bike

The Lifespan Of A Bottom Bracket

Putting aside the external factors like storing conditions and frequency of use, a bottom bracket’s lifespan will vary with the type of bike you install it on. 

Specifically, a bottom bracket used for casual road rides can function excellently for at least 5000 miles. On the other hand, for mountain climbing or sporty performances, this part can last for about 2000 miles.

Friction is the most dangerous threat to the intact condition of a bottom bracket. After a time of constant use and improper maintenance, the metal ball bearings will deteriorate, resulting in damage to the component. 

You must keep your bike hygienic, clean the crankset, and regularly grease the bottom bracket to expand its lifespan.

bottom bracket bike

When To Replace A Bottom Bracket?

If one of these symptoms shows up, it’s time for you to think of removing the existing bottom bracket on your bike.

  • The unusual sound: The creaking and grinding sounds are the most obvious signs of a worn-out bottom bracket. 
  • The unstable crank: You check the crank with your hands. Gently wiggle the crank or rotate the pedals. If the crank doesn’t move on a horizontal line with the bike’s frame, there must be an issue with the bottom bracket.
  • Check the bottom bracket’s rotation: Make sure the seat post is in a steady position, then rotate the crank. You will spot a worn bottom bracket if you can sense the vibration while rotating the crank. Moreover, you can feel significant resistance, and the grinding sound starts to occur. 

Bottom Lines

Although the bottom bracket on bike is a small item, it is responsible for the proper rotating mechanism of the whole bike. Getting to know about this part will considerably assist you in enriching your knowledge of cycling. 

Furthermore, you can upgrade and adjust your beloved bike with suitable components for smooth and safe rides. 

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