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A Regular Cyclist's Handbook of Bottom Brackets

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For children, a cycle is an excuse to get out of the house. With fuel emissions and global warming being in the headlines every other day, cycling is no longer just for the little ones. For adults, it is a means of commuting and exercise, and a passion to pursue. Infac,t you should check out the top 10 reasons why cycling is better than driving. It isn’t just the reasons for cycling that evolve with time. With age also comes a better understanding of the technical aspects of cycling. Instead of baskets, flags, and pompoms, your focus now shifts to smaller parts that can affect the efficiency of your bicycle. One such part is the bottom bracket. This is one of those tiny parts that gets barely any attention but plays an important role in making your ride enjoyable.

A bottom bracket may be the tiniest part of a cycle. But don’t you judge it by its size! This tiny part can change your experience of cycling for good or bad. Needless to say, it is important that you choose bottom brackets taking into account many factors such as spindle length, shell length, type of threading, etc. Here is a rundown of everything a regular cyclist should know about the various types of bottom brackets available today.  

What is a Bottom Bracket?

First things first! 

A bottom bracket, also known as a hanger, is what connects the bicycle frame to the crankset or chainset. It is installed in a shell and located where the seat tube meets the down tube. It can be best described as a spindle with two sets of bearings. The main function of it is to allow the crankset to spin freely while you pedal. It also carries the lateral and torsional loads produced while pedalling.

Did you know there are variants of bike pedals? Check out the best bike pedals that would add a thrill factor to your cycling. If you begin to feel that you need to work harder to pedal, you may need to take a closer look at your bottom bracket. 

what is Bottom bracket?
Bottom Bracket (source)

They are available in a number of different sizes and types. When it comes to types, it can be categorized as follows:

  • Threaded bottom brackets 
  • Non-threaded bottom brackets

The A to Z of Threaded Bottom Brackets

Do you know that the design of a threaded bottom bracket is probably as old as the bicycle itself?

This is designed to be screwed inside a threaded bottom bracket shell.

These can be further categorized as cup and cone bottom brackets, cartridge bottom brackets, and external bearing bottom brackets. 

Threaded Bottom Brackets

1. Cup and Cone Bottom Brackets

This is one of the earliest types of threaded bottom brackets. It can be identified by a notched locking on the side away from the chain and a flat cup face. These brackets need regular maintenance to function optimally. By the 1990s, most bicycle manufacturers had phased out of this type in favour of cartridge bottom brackets. However, many bicycles intended for riding on roads still use these cup and cone Bottom Brackets.

2. Cartridge Bottom Brackets

In this type, the sleeve, spindle, and bearings are considered a single unit. Hence, when its bearings wear out, the entire unit needs to be changed. Cartridge bottom brackets have a number of advantages. Since the unit is sealed, it has a longer life. It is also easy to replace and not very expensive. There are a number of variations to this type and below are the following:

3. Threading

Based on the common types of threading used, cartridge bottom brackets can be divided into two - the English (BSA) threading and the Italian threading. The English threading has a diameter of just about 35mm while Italian threading has a 36mm diameter. English threading has a right-hand thread on one side and a left-hand thread on the other.

As a result, the thread direction always follows the pedalling direction. This is also known as reverse threading. On the other hand, Italian threading has a right-hand thread on both sides. This is believed to increase the chances of the bottom bracket loosening on the non-drive side. 

4. Crank Interface

Older versions of a cartridge type have a tapered spindle with a square profile. Newer versions that fit Octalink cranksets feature a splined spindle. One of the other common splined standards is known as the ISIS standard. The splined spindle increases the life of the bottom bracket and makes it stiffer. 

5. Width of the Shell

Most English threaded bottom brackets have a 68mm shell width or 73mm shell width. The latter is usually seen on mountain bikes. The shell of an Italian threaded bottom bracket is usually 70mm wide. 

6. External Bearing Bottom Brackets

The limitations of cartridge bottom brackets led to the evolution of external bearing brackets. These are the latest form of threaded bottom brackets. They may also be referred to as conventionally threaded bottom brackets. These are designed in the form of a hollow sleeve with bearings in sealed cartridges at both ends.

One of the limitations of the cartridge bottom brackets addressed by this type is the short bearing life caused by a small spindle. Since these bearings are placed on the spindle, they are not limited by size. Hence, this category of brackets usually features bigger and stiffer bearings and spindles. Today, these are a standard feature in mountain bikes and other high-end bikes with threaded bottom brackets. 

The A to Z of Non-Threaded Bottom Brackets

One of the core differences between a high-end bicycle and a low-end bicycle is the weight of the frame. As the price increases, the weight decreases. With the advent of carbon fibre, bicycles became much lighter. One of the expected uses of this material was in the construction of bottom brackets. However, carbon fibre was not suited for certain processes such as facing or threading.  

In order to use carbon fibre, the bearings needed to be placed in threaded sleeves that were then bonded to the shell. This added weight to the frame and hence a more elegant solution was needed. The ability of carbon fibre to be moulded into different shapes led to the development of the non-threaded bottom bracket. Some of the main bottom bracket standards that have evolved since then are:

1. BB30

This was one of the first non-threaded bottom brackets. It was manufactured by Cannondale and premiered at the 2000 Tour de France. It is considered to be the design from where the press fit revolution took off. This design features a spindle with a 30mm diameter and 42mm frame shell with bearing pressed into it. 

According to a few BB30 bottom bracket reviews, there are two possible press fit complications that could occur. A loose press fit may allow the bearings to move about thereby creating a creaking noise. On the other hand, if the shell is too small in comparison to the bearings, it could affect the smoothness of your ride. But you can have a smooth ride with the right bike maintenance and oiling. This can be fitted on to non-BB30 cranksets with the help of an adaptor.

If you were wondering about BSA bottom bracket vs bb30? Then we suggest you opt from BB30! BB30 is stiff, performs better, has longer bearing life and the best thing light in weight.

However, a newer variant of this design has entered the race and is called the BB30A. This features an asymmetric shell and wider spacing between the bearings. These changes increase the life of the bearings and improve support. 

bb30 bottom bracket review

2. BB90/95

As in the above design, the bearings fit directly into the frame of this bottom bracket. However, it has a narrower spindle with a diameter of only 24mm. At a width of 90mm for road bicycles and 95mm for mountain bicycles, they have a much wider shell. This gives designers more area to place suspension pivots and gives them the freedom to experiment with tube profiles. Going wider than this is not recommended as it could affect the chainline and dynamics of pedalling. 

mountain bike bottom bracket types

3. PF30

The PF30 bottom bracket is comparable to the BB30. It shares the same spindle diameter indicating that this can be used on a crank shaft designed for the BB30. Road bicycles with this bottom bracket have a shell width of 68mm and mountain bicycles have a shell width of 73mm. The difference between the BB30 and the PF30 lies in how the bearings are placed. In the BB30 they are pressed directly into the frame while the PF30, they are fitted into nylon or aluminium cups. This increases tolerances while manufacturing the piece and thus reduces its cost. 24mm cranksets can be fitted with a PF30 bottom bracket by using an adaptor. 

4. PF86/92/121

Like the PF30, these do not have the bearing pressed directly into the frame. However, with a diameter of 24mm, the spindle is comparatively narrower. This is similar the BB90/95 standard. The shell width of this when used for regular bicycles, is 86mm while mountain bikes have a shell width of 92mm. For fat-tired bikes, a special shell with a width of 121mm may be used. 

bsa bottom bracket vs bb30

5. BBRight

This is a variation of the BB30 and the PF30 systems. The spindle has a 30mm diameter and the shell width measures 79mm. This system is set apart from others by its offset shell. Offsetting the shell results in a significant increase in stiffness and reduced frame weight. This is available in both a direct fit and press fit. 

bicycle bottom bracket bearings

6. BB386EVO

This design was introduced in 2011and combines features of the BB90/95 and the PF86/92. From the BB90/95 it borrows the 30mm spindle and from the PF86/92 it takes the 86.5mm wide shell. This increases the bearing stiffness and strengthens the chainstay area. These cranks are compatible with almost all BB shell standards. 

bb86 crankset compatibility

7. T47

This was introduced in 2015 and is the latest bottom bracket standard. It can be described as a threaded bottom bracket that can work with larger spindles and is compatible with other shells. Thus it completes a circle as far as the evolution of bottom brackets is concerned. The system can work with a spindle measuring 24mm or 30mm diameter and shells that are 68mm, 73mm, 83mm and 100mm wide. This design solves the creaking issues associated with other press fit systems. 

Bottom Bracket Cups
T47 (source)

Threaded vs Non-threaded Bottom Brackets

Though threaded bottom brackets may be considered old school, they are still quite popular. One of the reasons for this is because they are compatible with the largest number of cranks. Unlike press fit bottom brackets, no special tools are required to maintain the brackets. If improper tools are used to adjust bearings in a press fit system, the frame is likely to be damaged. Press fit brackets are also notorious for creaking which the threaded brackets are not subject to. However, threaded bottom brackets are a lot heavier. 

The decision between threaded and non-threaded bottom brackets could also be influenced by their aesthetics.

While the BB30 is known for its sleek form, a threaded bottom bracket may offer steel cycle frames a more proportional look. Hence, when it comes to picking the perfect one, there are a number of pros and cons to be weighed. 

Mountain Bike Bottom Brackets

Mountain bike bottom bracket types can be categorized as Euro, Mid or Spanish bottom brackets. A Spanish bottom bracket differs from Euro brackets in the size of the bearings. This system was designed by a BMX company known as Fly Bikes and uses lighter and smaller bearings. 

Why is Spanish bottom bracket everyone’s favourite? Well, It features smaller shell, slimmer frames that help further reduce weight. Also, it is highly reliable. This is a huge advantage for mountain bikes that are ridden over rough terrain.

So, when are planning for a mountain bike ride? 

Spanish Bottom Bracket

Know the Difference: Bottom Bracket Height v/s Bottom Bracket Drop

Bottom Bracket Height

One of the measurements related to a bottom bracket that can affect your ride is the height. This can be defined as the measurement from the centre of it to the ground. A chief factor that influences this measurement is the thickness of the tires. The thicker the tires, the more the height will be. 

Bottom Bracket Drop

Many people mistake bottom bracket height with the bottom bracket drop. The latter is the measurement between the center of the wheel and the centre of the bottom bracket. 
Increasing or decreasing the height makes no difference to the stability of the bicycle. However, it can improve your cross-country riding experience. It can also make pedal clearance on corners easier when riding on roads.

Raising it on a criterium frame also makes the frame more rigid and responsive. On the flip side, it can make it difficult for your foot to reach the ground when you stop.  

Changing from one Bottom Bracket Standard to Another

With time, all the parts of a cycle undergo a lot of wear and tear. Cycles that are ridden every day should be overhauled at least once a year while mountain bikes should be overhauled twice a year. This helps identify problems in their nascent stages and can save you major expenses. Some of the common causes of this wear and tear are exposure to mud and water and improper handling. Eventually, the bicycle bottom bracket bearings or the unit as a whole may need to be replaced. 

It is not necessary for you to stick to the bottom bracket that your bike was manufactured with. However, you will need to match the size of the crankset, the interface type, and the shell width to ensure that the new bottom bracket fits our cycle’s frame. 

Today, there are a number of adapters available that can help you switch from one system to another. However, a direct conversion is always considered a better choice. This minimizes the number of parts involved and in turn, reduces the number of interfaces that could create a problem. 

bottom bracket
Bottom Bracket Standard (source)

How does Changing Bottom Brackets Affect the Chainline

The chain line refers to how the chain runs between the front and back sprockets. In an ideal situation, both the sprockets should be in the same line so that there is no stress on the chain. To determine your bike’s chain line, measure the distance between the center of the chain and the centre of the frame. If your bike has a double chain wheel, measure the distance from between the two rings and if it has a triple chain wheel, take your measurement from the middle ring. 

Different cycles have different chain line standards. Changing the bottom bracket can affect this chain line. Replacing it with one that uses a shorter spindle will move the chain line towards the left. It is important to ensure that there is enough clearance between the frame and the crank before doing this. 

The search for the perfect bottom bracket continues. It may not always be advisable to change it only on the basis of the latest models available in the market. While each different type of bottom bracket may offer different theoretic advantages, you must also consider the ease of maintaining it on the road. Both threaded and non-threaded bottom brackets have a number of loyalists. In your experience, which one has given you a better ride? Share your experience with us. 

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