Sprockets

What is a BMX Sprocket and what is its main purpose?

The BMX sprocket (or chainring) is mounted on the crank and transfers your pedaling power to the chain. Its size (number of teeth) determines how hard it is to pedal and how fast you can go (gear ratio). It also needs to be strong enough to withstand impacts from grinding and crashes.

How is a BMX Sprocket constructed?

Teeth

The outer ring that engages the chain. Common sizes are 25T or 28T for Freestyle, and smaller sizes (e.g., 22T) for Flatland.

Bore / Center Hole

The hole in the middle where the crank spindle passes through. Usually 23.8mm with adapters for 19mm or 22mm axles.

Drive Hole

The mounting point for the sprocket bolt (on Bolt Drive sprockets) that fixes the sprocket to the crank arm.

What types of Sprockets are there?

Bolt Drive

The standard system. The sprocket is fixed to the crank arm with a bolt. Compatible with almost all cranks.

Spline Drive

The sprocket has a hardened steel insert with teeth (Splines) that matches the crank spindle (usually 48-Spline / 19mm or 24mm). No sprocket bolt is needed. Requires a matching 48-spline spindle!

Micro Drive

Sprockets with fewer than 25 teeth (e.g., 22T). Primarily used in Flatland to provide clearance for tricks and an easier gear ratio. Note: Requires a specific crank mounting hole (Micro Drive bolt).

Guard Sprockets

Feature a built-in or replaceable guard (bash guard) to protect the chain and teeth from damage when grinding rails or ledges. Essential for street riding.

What materials are used for Sprockets?

7075-T6 Aluminum

The industry standard for high-end sprockets. Very hard, durable, and lightweight. Often CNC machined.

6061-T6 Aluminum

Slightly softer and cheaper than 7075. Good for budget-friendly sprockets.

Steel

Basic stamped steel sprockets are heavy and prone to bending. They are cheap alternatives found on entry-level bikes and not recommended for serious riding.

Nylon / Plastic (Guards)

Often used for the replaceable guard rings on sprockets to reduce friction while grinding.

Which Sprocket size (Teeth) is right for me?

The standard gear ratio for modern Freestyle BMX is 25/9 (25 teeth front, 9 teeth rear driver). However, personal preference plays a role:

How do I install a BMX Sprocket?

1. Remove the crank arm and old sprocket.
2. Check Spindle Size: Ensure you use the correct adapter ring (19mm or 22mm) if your sprocket bore is larger than your spindle.
3. Alignment: Place the sprocket on the spindle. Ensure it aligns perfectly straight with the rear driver to prevent chain issues.
4. Tighten: For Bolt Drive, tighten the sprocket bolt securely to the crank arm. For Spline Drive, simply slide it on (it locks via the splines).
5. Reinstall the crank arm and chain.

What do the specifications mean for BMX Sprockets?