BEGINNERS GUIDE TO BOTTOM BRACKETS

Shaun George BOTS Guides, Mechanics, Tips & Tricks

The bottom bracket or “BB” is a very important component on the bike frame. It’s found in-between the frames seat tube and bottom tube in a hollow opening called a “BB shell” which consists of two bearings, one on either side.

The Bottom Bracket essentially connects the crankset to the bicycle and allows it to rotate freely. It contains a spindle that the crankset attaches to. The bottom bracket fits inside the BB shell which connects the seat tube, down tube and chain-stay as part of the bicycle frame.

A good quality Bottom Bracket can last thousands of kilometers and many years if taken care of. However, wear and tear does get to the bearings and cause squeaks and some rough spots along with “play” in the crank.

When replacing your Bottom Bracket there are a few things to consider.

WHAT DEFINES A GOOD BOTTOM BRACKET?

A good bottom bracket is a “fit it and forget it” deal. A sealed unit is what’s current and popular because it doesn’t require any servicing. They last a long time and can easily be replaced if they wear out. Newer bottom brackets are wider (making them significantly stiffer) and more durable than ever before,

The most common types of bottom brackets are the traditional/square taper and press-fit bearings. Generally, the higher up you go in a components hierarchy the better the quality of the bearings and quality of materials become, this is reflected in pricing.

WHAT TO LOOK OUT FOR

To a certain extent which bottom bracket you end up buying is up to what kind of frame you have. Certain frame materials and drivetrain options only support one type of Bottom Bracket. There are two main types of bicycle bottom brackets in today’s market, namely, threaded and press-fit BB’s. 

The quality of bearings in your bottom bracket is another area of importance if you want the best out of your upgrade. You would want to look at bearings made of strong and low friction materials such as ceramic bearings in Bottom Bracket’s as they have very low resistance and have a much longer life than say, steel bearings that are in most Bottom Bracket’s these days.

The bearings are highly important, as their quality dictates how much energy is lost as friction and how long they’ll last over heavy usage. If they are within your budget, fully sealed cartridge bearings are the most preferable. They are non-adjustable, non-serviceable units that don’t need any maintenance but have to be thrown away when they are worn out – The ideal setup when you’re riding in rainy and muddy conditions.

More expensive units use bearings that have much higher tolerances, resulting in less friction and longer life. MTB bottom brackets often have a larger amount of sealing for the increased demands of off-road use.

COMMON BOTTOM BRACKETS

1. CARTRIDGE TYPE BOTTOM BRACKET

This is an old type of Bottom Bracket that has a short spindle length and a sealed internal bearing cartridge. This type of bearing is still commonly used amongst the cheaper makes as it is a simple Bottom Bracket to work with. Once the Bottom Bracket wore out it was just thrown out and swapped with a new one, instead of opening it up and messing with the bearings.

2. THREADED/ EXTERNAL BOTTOM BRACKET

Threaded Bottom Brackets are actually of quite a few kinds. The older and cheaper designs found even today on budget bikes basically have bearings that sit inside the frame with a fixed axle that the crank arms are tightened onto.

There are a huge array of standards for the fixed axle designs. The most common and cheapest type is the square taper interface. Shimano offers a multi splined bottom bracket design similar to the square taper called the Octalink interface.

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On more modern designs, there’s a  three-piece construction that has a pair of larger diameter bearings that sit outboard (outside) of the bottom bracket shell, with an axle that is permanently fixed to one of the crank arms. The bearings are placed in aluminum cups outside the Bottom Bracket shell to help in the provision of longer axle lengths and more torsional rigidity for effective power transfer.

3. PRESS-FIT BOTTOM BRACKET

Pressfit Bottom Brackets don’t screw into the Bottom Bracket Shell. These Bottom Brackets are now commonly found on mid to high-end bicycles in almost all disciplines. Here the bearings are directly “press-fit” into the frame. This allows for wider BB shells without affecting spindle length. The BB shell as a result also becomes stiffer and lighter. Transfer of power is also more efficient as there is less BB flex. 

Here the quality of bearings is very important as it will dictate how much power is lost via unnecessary friction. The best way to avoid this would be to get fully sealed bearings cartridges. They aren’t adjustable but require no maintenance. It’s a use and throw kind of a deal. Once the bearing is shot, just toss it into the bin. Pressfit systems require incredibly high tolerances and the highest standards in quality control in frame manufacturing for it to function at its absolute best.

Press-fit Bottom Brackets are notorious for “creaking” – this creaking sound takes place if water or contaminants make their way into the Bottom Bracket shell. It can also happen from improper BB installation or insufficient greasing. Proper installation is super crucial here, the bearings must sit flush with the Bottom Bracket Shell and for this, you will need specialty tools.

Most bikes these days come with Press-fit BB’s as standard because they’re very reliable and are easy to manufacture.

WHICH ONE DO I NEED?

Almost all older and budget bicycles come with threaded Bottom Bracket Shells. Press-fit is relatively new and easy to identify. If you can spot additional protrusions from the BB Shell (outboard cups) then you have new-age threaded bottom bracket. This type of BB is usually found on new mid-range to high-end road and Mountain bike. If you’ve got a carbon bike then you’ll most likely have a Press-fit Bottom Bracket. That isn’t certain though.

To accurately identify the Bottom Bracket shell in your frame, it is important that you remove the crank arms and bottom bracket from the frame. A few manufacturers such as Cannondale use asymmetrical Bottom Bracket shells which may require a very specific bottom bracket. However, the majority of them are the standard symmetrical Bottom Bracket shell. Some older frames may have Italian threaded bottom brackets though-instead of the more modern English.

To know the size of Bottom Bracket that you require, simply measure the length of the inside of your Bottom Bracket shell. It’s usually 73mm or 68mm on all modern bicycles.

Older bicycles may have the less conventional Italian threaded Bottom Brackets, unlike the more modern English Threaded Bottom Brackets.

The English variants use left-handed threads on the drive side, whereas Italians use a right-hand thread on both sides. If your bicycle frame isn’t too old you’ve probably got an English thread yourself.

Another famous Bottom Bracket is the BB30 by Cannondale which allowed the use of chainsets with larger 30mm spindles and bearings

While you have a restricted choice when it comes to Bottom Brackets. You have greater freedom when it comes to the quality of the Bottom Bracket. Bottom Brackets at different price points will differ when it comes to weight, materials used, efficiency and longevity.

Another very important aspect of buying a new Bottom Bracket is compatibility. Knowing how compatible your Bottom Bracket is to your frame or to your crank and frame geometry is very important before making the investment. Visit your local bike shop and consult the mechanic as to how to go about the process.


SUMMARY

After the purchase you must keep in mind that a Bottom Bracket is a high wear and tear component, taking proper care of the component will save you a lot of time, money and effort in the long run.  

Bearing quality is also an important consideration when looking at a Bottom Bracket. If you’re not confident about installing or removing a bottom bracket, take the bike to a bike shop near you – working on it without prior experience can cause problems.

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