How to choose your road bike chainrings?

Road chainrings are certainly one of the most complicated components to replace when you want to fit something other than what the manufacturer intended. Let us try to lay down the basics to help you choose this part without making a mistake.

The standards

Number of speeds: currently 9, 10 or 11
Indexing
The bolt circle diameter
Tooth count
The mounting standard

Chainring standards and types

All the components of a drivetrain are designed to work under a specific speed standard, so you cannot pair a chainring designed for 10-speed with an 11-speed drivetrain, for example. Today, most road bikes run on 10 or 11 speeds, although 9-speed can still be found.

Please note that indexing* differs between manufacturers, so all the chainrings on a crankset must be at least from the same brand.

The bolt circle diameter of a chainring, also known as the BCD*, is the diameter of the circle that could be drawn passing through the centre of the chainring bolts. To measure it, on a 4-arm crankset you can measure the centre-to-centre* distance between 2 fixing holes directly opposite each other; for a 5-arm crankset, measure the distance between 2 consecutive fixing holes and refer to the diagram.

The tooth count of chainrings works in the opposite way to cassettes: the fewer teeth a chainring has, the less effort is required.

Finally, the point that causes the most issues: the mounting standard. Today, cranksets are increasingly optimised with specific interfaces between the chainrings and cranksets. Even if the bolt circle diameter often remains conventional, the position and/or the method of fixing the chainring can differ. On this type of crankset, it is therefore important to correctly identify the specifications when fitting or adapting a new chainring.

Which chainring for my crankset?

When you want to replace a chainring, you may not necessarily have a choice: the simplest and most reliable option will generally be to go for the chainring from the crankset manufacturer that is specific to the model you have.

If however you opt for an aftermarket option, be aware that you can find chainrings with specific technologies to improve shifting reliability (Stronglight CT², for example).

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