BMX Chains, Sprockets and Freewheels

Single Speed

The BMX runs on single speed: one chainring at the front, one sprocket at the back, with no derailleur. Its chain, wider than that of geared bikes, at an eighth-inch pitch, withstands the intense efforts of starts and tricks. The half-link chain, adjustable link by link, allows for precise length adjustment, which is useful with a small sprocket.

The Transmission

The BMX transmission also comes in:

• Chainrings.
• Cranks.
• Cables and Housing.

All the transmission parts are available on the transmission page.

The Right Ratio

The gear ratio depends on the relationship between the teeth of the chainring and the sprocket. In freestyle, riders use small chainrings, around twenty-five teeth, with a nine-tooth sprocket, on a cassette hub or freecoaster: a compact setup that doesn’t touch the edges. The screw-on freewheel, simpler, equips entry-level BMX bikes. In racing, riders adjust their gear ratio based on the track and their power.

Adjustment and Maintenance

The chain must be taut without being stiff: keep about a centimetre of vertical play in the middle of the lower strand. Tension is adjusted by sliding the rear wheel back in its dropouts, and the axle nuts must be tightened securely. Chain tensioners prevent the wheel from moving forward. The chain should be cleaned and lubricated regularly, and replaced as soon as it stretches or skips.

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Frequently Asked Questions

What gear ratio should I choose for a BMX freestyle?

In freestyle, the modern standard pairs a small chainring with twenty-five teeth and a nine-tooth sprocket. This compact ratio provides good starts and gives ground clearance under the pedals for grinds.

What is a half-link chain?

All its links are identical, allowing the chain to be shortened or lengthened one link at a time, rather than two. This way, tension can be adjusted precisely, without a tensioner, even with a small sprocket.

How do you adjust the tension of a BMX chain?

Loosen the rear wheel nuts and slide the wheel back in its dropouts until the chain has about a centimetre of play. Ensure the wheel is aligned properly before tightening securely.

Screw-on freewheel or cassette hub on a BMX?

The freewheel screws onto the hub, which is simple and cost-effective. The cassette hub, with an integrated mechanism, is more robust and accommodates the smallest sprockets, starting from nine teeth. The freecoaster even allows you to ride backwards without engaging the pedals.

Why does a BMX chain derail?

Most often due to insufficient tension, a worn sprocket or chainring, or a misaligned wheel. You should retighten the chain, check the alignment, and replace any parts that have teeth shaped like hooks.