Cassette Hub

A cassette hub is a BMX rear hub that uses a removable driver with a ratchet inside. When you pedal forward, the driver locks to the hub and drives the wheel. When you stop pedalling, the wheel keeps spinning without turning the cranks.

What it does

The hub is the centre of the rear wheel. It holds the axle, the bearings and the driver. The chain runs around the driver, and the driver connects to the hub shell through a ratchet mechanism.

Inside the driver are small pawls that engage a toothed ring on the hub shell. Pedalling forward makes the pawls lock into the ring. Rolling forward without pedalling makes them click over the teeth, which is the sound you hear when you coast.

Rolling backwards does the reverse. The pawls lock, so the wheel drives the cranks backwards. This is why a cassette hub is not suited to riders who want to roll backward while the pedals stay still. For that, see the freecoaster hub.

Types and standards

Driver size

The driver is the small gear the chain runs on. Its tooth count combines with the sprocket to set the gear ratio. A 9 tooth driver is standard on modern BMX. Other sizes (10 to 14 teeth and larger) exist, but they require a bigger sprocket to keep the same ratio.

A smaller driver lets you run the same gear ratio with a smaller sprocket. That keeps the drivetrain compact and compatible with more frames.

Axle size and style

Axle	Notes
14mm	The standard for freestyle. Strong and stiff.
3/8 inch (about 9.5mm)	Found on entry level hubs. Lighter, but bends more easily.
Male axle	The axle end is threaded, and nuts hold the wheel on.
Female axle	The axle is hollow and threaded inside, and bolts screw in from each side.

Male axles leave threaded ends sticking out past the dropout, which is where many hub guards clamp on. Female axles have a cleaner finish with no protruding threads, but they need bolts and guards made for them.

LHD and RHD

Almost all hubs are RHD (right hand drive), with the driver on the right. LHD (left hand drive) hubs put the driver and the chain on the left. Some riders choose LHD because they prefer the drivetrain on that side. The sprocket and chain line must also sit on the same side, so check that your frame and cranks suit it.

Spoke count

Rear hubs are drilled for 36 or 48 spokes. A 48 spoke wheel is stronger for heavy street use. See rims for what matches.

Sizing and compatibility

1. Rear spacing: BMX frames use a 110mm rear dropout width (the old standard). Check your frame.
2. Axle diameter: The dropouts need to fit your axle. Check that the slot is wide enough for a 14mm axle. Some older frames only take 3/8 inch.
3. Spoke count: Match the rim's drilling.
4. Driver thread or spline: Drivers are specific to the hub brand and model. Do not assume they swap.
5. Brakes: If you run a rear brake, see brakes. The rim needs a machined brake surface.

How to choose

1. Decide on a cassette or freecoaster first. If you are on a budget, or ride dirt or park, a cassette is a sensible pick.
2. Choose a 14mm axle for freestyle. It handles hard landings better.
3. Pick 36 spoke for a lighter wheel. Pick 48 spoke for a tougher one.
4. Take a 9 tooth driver, then pick a sprocket for the ratio you want.
5. Match the axle style (male or female) to your hub guards.

Cassette hubs are the lower priced option compared with freecoasters. Quality sealed bearing hubs cost more than basic hubs, but they last longer.

Maintenance

• Check axle nuts or bolts are tight after the first few rides. A loose axle can chew up the dropouts.
• Regrease the driver and pawls every few months, and more often if you ride in wet or dusty conditions.
• Listen for a gritty or grinding hub. That usually means worn bearings.
• If the pawls start slipping, the hub will skip under load. Replace the driver or the pawls.
• Keep the chain and sprocket clean to reduce driver wear.
• See BMX maintenance basics.

Related parts

Freecoaster hub, front hub, sprocket, chain, hub guards and rims.