Understanding bicycle crank sets

What constitutes a crankset?

Cranks

The crank is the part that connects the pedals to the chainrings.

The crank spec to check when selecting a crankset is the “crank length. The pedaling circumference changes as the crank length changes.

Also, since cranks are connected to chainrings by arms, the “number of arms” and “PCD,” which is the distance between arms, determine the compatible chainrings.

In the case of cranks with integrated shafts that connect the crank to the left and right cranks, the shaft length and shaft diameter are also important.

Since this is the part that transmits the force of pedaling, advanced riders with more power prefer cranks with higher rigidity.

However, users who require high rigidity also demand lightweight cranks, so cranks of higher grades are made hollow (hollow inside) or made of carbon to achieve both high rigidity and lightweight. Naturally, they are also more expensive.

Chainrings

The gear attached to the crank is called the chainring. The chainring is the part that connects the crank to the rear sprocket.

In bicycles, the gear ratio is determined by the combination of the number of teeth on the chainring and the rear sprocket. Therefore, by customizing the number of teeth on the chainring, you can change the overall weight and speed direction.

Chainrings cannot be installed unless the number of gear arms on the crank arms and the PCD, which indicates the magnitude of rotation, match. Also, if the number of ring teeth and chainline do not match, the derailleur will not be able to change gears correctly.

Shaft

The shaft is the rod that connects the left and right cranks and rotates the chainrings.

Some models, such as Shimano’s HOLLOWTECH II, have the shaft integrated with the crank arm, while others, such as the Square BB, have the shaft integrated on the BB side.

Each requires a corresponding BB (bottom bracket), and the compatibility of the corresponding BB with your bike will determine if you can use that crankset.

Crankset Compatibility

BBs determine the compatibility of cranksets.

Of the Barts that make up a crankset, except for the chainrings, compatibility is determined by the BB standard. The BB standard here is both the BB that the crankset fits and the BB that the bike frame fits.

For example, Shimano’s current cranks are based on the Hollowtech II standard, so they can be installed as long as the part (BB shell) where the BB is mounted on your bike is the BB standard that is lined up for the Hollowtech II BB.

Note that most bicycles for the Japanese market use 68mm wide threaded BBs, but foreign manufacturers may use their own BB standard such as MegaExo or BB65.

In principle, chainrings can be installed as long as the number of gear arms and PCD match.

Among cranks, the number of crank arms and PCD basically determine chainring compatibility. As long as these match, chainrings of other manufacturers and different grades can be installed.

For example, if the number of crank arms and PCD are the same, it is possible to install a higher grade ULTEGRA chainring on a Shimano 105 crank.

However, there are rare cases in which the shape of the attachment points are unique, so be sure to use a combination that the manufacturer claims to be compatible.

Be careful when changing the number of gear teeth or steps.

The crank chainring is a part of the component, so changing this part will affect the derailleur.

There is no problem if the parts are officially declared compatible by the manufacturer, but if they are combined outside of compatibility, it is important to understand that if the number of gear steps changes, the thickness and position of the chainrings will be different, which may cause problems in shifting gears.