Cassette drivers

BMX cassette drivers: the heart of the rear hub

The cassette driver, or freehub body, is the part of the rear hub that carries the sprocket and passes pedalling power to the wheel. It houses the pawl mechanism that engages under power and lets the wheel spin free when you stop pedalling. It is a wear part: on a well-kept hub you replace the driver and its pawls, not the whole hub.

Spotting a worn driver

Three symptoms give it away. Engagement that keeps you waiting just as you throw yourself down the gate, a sharp crack under load, or an irregular click when freewheeling. A silent hub that slips points the other way: pawls stuck down by grease that is too thick. Strip it before ordering, since a clean and a new set of springs is often all it takes.

Pawls, springs and lock rings

The pawls are the metal fingers that drop into the ratchet teeth inside the hub. They round off with the miles, and their springs lose tension long before they do. The lock ring holds the sprocket on the driver: it is the part that suffers at every sprocket change and whose thread marks quickly if you force the fit.

• Pawls: replace as a full set, never individually
• Springs: the cheapest part, change at every driver service
• Lock ring: check as soon as a sprocket develops side play
• Spacers: to trim chainline to a tenth of a millimetre

End caps and hub interfaces

End caps close the hub and bear against the frame dropouts while keeping mud out of the bearings. They are chosen by axle diameter: a cap made for a 10 mm axle will not fit a 15 or 20 mm build. If you are switching standard, order the caps at the same time as your BMX wheel axles.

Compatibility: a matter of the exact model

There is no universal driver. Every manufacturer has its own spline geometry, pawl count and thread pitch, and versions change from one generation to the next within a single range. Before ordering, note the hub brand, the model and, where it is engraved, the version. Check the cog type you run too: a cassette driver cog is splined and retained by a lockring, never bolted on, and it will not fit a threaded freewheel hub, where the teeth screw on with the mechanism. Spline patterns also differ from one driver brand to the next. Our BMX hubs listings state the original driver for each reference.

Points of engagement

The more points of engagement a driver has, the shorter the dead angle between two teeth, and the faster the drivetrain answers the first pedal stroke. It is noticeable out of the gate and in pumping accelerations. In return, a very fast mechanism needs light grease and closer servicing. On a training bike or in the younger classes, a conventional driver stays more forgiving.

Servicing and service life

Strip the driver twice a season, or after a race in the rain. Clean the pawls and ratchet teeth with degreaser, dry them, then reapply a light freehub-specific grease — thick grease sticks the pawls down in cold weather. Check the sprocket seat and the lock ring while you are in there, and check chain tension: an over-tight chain wears the mechanism early. Matching parts are in our BMX drivetrain section.

The BMX RACING advice

Send us the brand and model of your hub, with a photo of the stripped driver if you can: we identify the exact reference, the matching pawls and springs, and tell you what should be replaced at the same time. Dispatched within 24 to 72 hours and you can spread the cost over 2 or 3 payments available.

A driver opens up the small cogs; what they do to the ratio is detailed in our comparison of ratios and rollout figures.