Ask a Mechanic | Using Steerer Tube Expanders with Carbon Forks

Zoe asks, “I need to adjust my road bike’s headset, but it has a carbon steerer tube and I’m not sure how to use the compression plug. Any advice?”

Most modern road bikes, even the aluminum-framed ones, have carbon forks with carbon steerer tubes. Because of the more delicate nature of carbon, setting a traditional star nut into the steerer tube as you would on an aluminum fork is no longer an option. That’s where a steerer tube expander, or compression plug as some call it, comes in handy.

A compression plug is set into a carbon fork’s steerer tube to keep your bike’s front end happy and tight, but should you need to pull the fork out of your bike or need to adjust your bike’s headset, you’ll need to know how to use the compression plug.

To remove a compression plug, use an appropriately sized allen and remove the top cap from the compression plug assembly. Before removing the compression plug itself, you’ll want to make sure that your stem bolts are still tight on the steerer tube so that you fork doesn’t drop out of the headset. Finally, using the necessary allen, loosen the compression plug and remove it from the steerer tube completely. You can now disassemble your stem, handlebars, and fork as necessary.

Before installing the assembly, make sure that the compression plug and top cap are pulled apart. The most important part about installing the assembly is that you install and tighten the compression plug completely before doing anything with your top cap or stem. This can be done with or without the stem on the steerer. Simply drop the compression plug into the steerer tube, use the appropriately sized allen wrench, and tighten the plug to the recommended torque spec. If you cannot find one, use 5Nm.

Install the stem onto the steerer if it wasn’t before, but don’t tighten the stem bolts. Then, making sure that you’ve got at least one spacer on top of your stem, install your top cap and begin to tighten it down. While grabbing your front brake, rock the bike back and forth. Continue tightening down the top cap until you no longer feel any knocking sensations and the handlebars still turn freely and easily.

If no amount of tightening eliminates the knocking, then add another 2.5mm or 5mm spacer on top of your stem and try it again. Once you have eliminated any knocking with the brake test and smooth steering, simply line up the stem and tighten the stem’s pinch bolts down to the manufacturer’s recommended torque spec.

Thanks for watching and get over to Art’s Cyclery for all your cycling needs!