​What is a Bike Bottom Bracket and How Do You Tell Which Type You Have?

What is a Bike Bottom Bracket and How Do You Tell Which Type You Have?

Mention the term Bottom Bracket to most cyclists and they may not know what you are talking about. The bike’s bottom bracket is one of those bike components that really don’t need a lot of attention from the majority of bike riders. Let’s discuss Bottom Brackets in a little more detail.

Bike bottom Brackets – Function

According to the article by Bicycling.com, your bottom bracket will typically be one of three possible types. Let’s describe each of the types in an historical sense from oldest to newest but first let’s explain what a bike’s bottom bracket is.

The Bottom Bracket is the point of contact for your bike’s crank arms and pedals. Both the left and right crank arms attach to the bottom bracket at your bike’s frame. The bottom bracket consists of bearings (steel, ceramic etc) which allows your crank arms to spin around the bracket’s pivot point. The spinning of the crank arms, obviously then spins your chain which spins your wheel which propels you.

​Bike bottom Brackets – Types

Bike bottom Brackets – Types
  • ​Square Tapered Bottom Bracket

Call this type the grandfather of bottom brackets. These were the first type of brackets to be installed on bicycles. Also known as the square tapered brackets, the crank arm is joined to the bracket using a square fitting interface. These types of installations were quite light weight but tended to wear out quickly. When worn, the entire unit needed to be replaced.

  • ​Spline Fit Bottom Bracket

Call this type the grandfather of bottom brackets. These were the first type of brackets to be installed on bicycles. Also known as the square tapered brackets, the crank arm is joined to the bracket using a square fitting interface. These types of installations were quite light weight but tended to wear out quickly. When worn, the entire unit needed to be replaced.

  • ​Two-Piece Bottom Bracket

​These types of bottom brackets are typically found on the higher end, more expensive bikes. These bracket types have the spindles permanently attached to the one of the crank arms (thus there are only 2 components versus the usual 3). The biggest advantage of these types of brackets is the fact that they have the bearings mounted on the outside of the units. When worn (which they will eventually), the bearing units can simply be removed and a new set installed. These types are also much stronger than the previous 2 as well.

​So in summary, there are 3 types of bottom brackets found on the typical bicycle. The differences probably wouldn’t be noticeable to the average rider but now that you have read this post, you will know the difference.

​I’m interested in taking a bit of a survey. Tell me (now that you know the difference between the types), which model of Bottom Bracket you have on your bike? Do you have the square end version, the spline fit version or the 2 piece external bearing version. I’m really interested in knowing!

So in summary, there are 3 types of bottom brackets found on the typical bicycle. The differences probably wouldn’t be noticeable to the average rider but now that you have read this post, you will know the difference.
Robert Flaherty
 

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