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This post compares the advantages and disadvantages of square taper and Octalink bottom brackets.

Definitions

Bottom bracket – a system of cups and bearings allowing a spindle to rotate inside the bike frame. The bottom bracket is placed in a small tubing serving as a connection point for the downtube and the seat tube. The cranks of the bike through which the rider transmits power to the chainring are fastened to the spindle.

Square Taper Bottom Bracket – a bottom bracket with internal sealed or semi-sealed bearings and a spindle with square tapered ends.

Octalink Bottom Bracket – A bottom bracket made by Shimano as a way to upgrade the old square taper bottom bracket. Octalink bottom brackets have a larger and stiffer spindle. The ends of the spindle have splines resulting in a more secure connection with the cranks.

The Advantages of Square Taper Bottom Brackets

1. Widely Available

Square taper bottom brackets have been the standard for decades. For that reason, the market is fully saturated with models ranging from generic production to units of superior quality with a multi-year warranty.

2. Serviceable

The bearings of modern square taper bottom brackets are sealed and therefore not serviceable. When the unit starts to complain, the user is expected to replace the entire cartridge.

However, the square taper bottom brackets found on older bikes from the 70s and 80s are fully serviceable.

If the spindle or the bearings are damaged, they can be replaced. Thus, older square taper bottom brackets can theoretically be used forever if serviced adequately. They’re also quite cheap.

The downside is that many bike shops do not store them due to the lack of demand.

3. Compatible With a Greater Number of Cranks

A square taper can be used with a great variety of cranks. It’s possible to install a crank from the 70s or one produced last year. The user can also rely on cranks from various brands. There is one exception, however – Campagnolo.

There are two square taper standards – ISO (Campagnolo) and JIS (Shimano, SRAM…etc.).

The JIS system is wider than the ISO. As a result, an ISO crank won’t go far enough on the spindle of a JIS square taper bottom bracket.

Meanwhile, Octalink cranks are limited to comparatively newer models produced by Shimano. Thus, if you’re looking for a variety of options Octalink does not fit the bill.

4. Larger Bearings

The bearing of square taper bottom brackets are larger and thus more likely to last longer. Of course, the longevity of the bearings is dependent on the quality of manufacturing too.

The Disadvantages of Square Taper Bottom Brackets

1. Rounded Crank Tapers

If a crank arm isn’t secured to the bottom bracket, it can start moving. The friction between the crank which is often made of aluminum (soft metal) against the steel (harder metal) spindle, can smoothen the square edges of the crank and thus make it impossible to secure the crank to the bottom bracket.

Octalink cranks don’t have the same problem because the splines result in multiple connection points. Thus, it’s less likely for the edges to get rounder.

2. Potentially Heavier

The table below compares the weights of square taper bottom brackets and Octalink models.

Conclusion: The weight of square taper bottom brackets and Octalink models is very close. However, high-end bottom brackets such as Dura-Ace BB-7700 offer close to 100 grams weight savings.

100 grams are not a lot in the world of recreational cycling but matter when competing on a higher level. That said, the people who want top performance are more likely to use an external bottom bracket such as Hollowtech.

The Advantages of Octalink Bottom Brackets

1. Lighter Stiffer Spindle

The main goal of Octalink was to save weight and make the spindle stiffer.

How?

During pedaling the bottom bracket spindle experiences a phenomenon known as torsion. Torsion represents the twisting of a unit via external force.

During torsion, most of the stress is on the outer layer/wall of the spindle. For that reason, a pipe is more resistant to torsion than a rod of the same weight and material.

Why? The pipe and the rod contain the same amount of material. However, in the case of the rod, a lot of the material is closer to the center. In the case of the pipe, all the material is part of its wall. Consequently, the pipe has a greater resistance to torsion thanks to its strategic composition.

The diameter of the pipe influences its resistance to torsion too. The greater the diameter, the stronger the pipe becomes. If two pipes are made of the same material and have a matching wall thickness, the pipe with the greater diameter will be stronger.

As a result, every increase in diameter gives the opportunity to make the pipe thinner without losing strength in comparison to the previous diameter.

The spindles of Octalink bottom brackets are a product of those principles and are therefore lighter and stiffer than square taper spindles.

2. Tight Connection to The Cranks

The splines on the spindle make it harder for the crank arm to get loose. Thus, Octalink bottom brackets are less likely to round the crank’s tapers.

The Disadvantages of Octalink Bottom Brackets

1. Small Bearings

Both Octalink and square taper models are internal bottom brackets and have their bearings within the bottom bracket body. Thus, the larger spindle of Octalink bottom brackets automatically results in the use of smaller bearings. If the size of the bearings is preserved, the spindle simply won’t fit in the body.

The smaller the bearings, the less durable they are. Hence why Octalink users have complained of the bearings’ longevity.

2. Overly recessed Splines

The first version of Octalink bottom brackets was designed primarily for road bikes and has a spindle with relatively short splines. When the same architecture was used on MTBs, the connection between the crank arm and the bottom bracket began failing.

The issue was addressed by creating Octalink 2 which has longer splines and is, therefore, better for more aggressive riding.

3. Possible Spline Damage During Installation

A major downside of Octalink is that the splines of the spindle are no longer visible once the crank arm is inserted. This creates the opportunity for inserting the crank improperly (out of the necessary groove).

If the user tightens the bolt when the crank arm isn’t properly fit, the spindle will dig new grooves into the crank and damage it. This could lead to failed splines and a loose connection between the cranks and the bottom bracket.

3. Limited Stock

Square taper bottom brackets are produced by a great number of companies. Thus, there are plenty of models to choose from in virtually every bike shop.

Octalink, on the other hand, is an exclusive Shimano product. Consequently, the user has to choose between fewer models. For the same reason, spare parts are scarce too.

Do Not Confuse Octalink with Isis

ISIS and Octalink bottom brackets look pretty similar on the outside, but the parts made for them are not interchangeable. Octalink spindles have 8 splines (hence the name) whereas Isis bottom brackets have nine. Also, the splines of Isis BBs are longer.

4. Limited Crank Compatibility

Octalink cranks are made primarily by two companies – Shimano and Suntour. Thus, the user has a smaller choice.

Conversely, square taper cranks have been here since the 60s. The user can install cranks ranging from retro models made by companies that no longer exist to modern versions.

This is a huge advantage of square taper bottom brackets because a very light setup can be acquired for cheap. For example, the user can purchase a new square taper bottom bracket and couple it with a high-end Shimano crank from the 80s that weighs 600 grams or less.

5. An Abandoned System

The Octalink system has been abandoned in favor of the newer Hollowtech generations. Thus, it is highly unlikely that Octalink will gain additional improvements.

Square Taper = Winner

An objective look at the data makes it clear that square taper offers more value for money. While Octalink is lighter and comes with a reduced chance of rounding the crank arm, the main downsides of the system are too big to justify its implementation.

In short, the benefits of a square taper bottom bracket over an Octalink model are:

• Huge variety of bottom brackets and cranks made by multiple brands
• Longer lasting bearings
• The same bottom bracket can be used for a road and an MTB bike
• More convenient crank installation
• Some models weigh as much or slightly more than Octalinks, thus the weight savings offered by Octalink are too slim to matter, especially to recreational riders.
• Octalink has a stiffer spindle, but the spindles of square taper bottom brackets are stiff enough for most people.

That said, Octalink bottom brackets offer solid performance and can last a long time. If you have a bicycle equipped with one, it makes no sense to replace the unit until needed.

Meanwhile, if you consider square taper bottom brackets archaic, you can always go for a newer, external bottom bracket such as Hollowtech and couple with it modern cranks.