At least on any bike I have worked on, once you get the compression plug in, you don't have to ever touch it again unless you are cutting the steerer. It just stays in the steerer. Any basic messing with the stem or swapping spacers does not require doing anything to the compression plug.

I might be missing something but assuming yo did not cut the stem, you might have taken it out for no reason. You can just put it back in, which is super easy, but if you took it out when you did not need to, a $30 lesson in stem/steerer working might be money well spent.


If I am wrong and you had a reason to take it out, it is super easy to get back in. Assuming it is not some sort of one off weird propriety setup, the compression plug basically sits in the steerer with a lip limiting how far in it can go so it just goes where it goes and gets tightened. I couldn't really see how you could get that part wrong as long as you use a torque wrench.

Wow. Someone would charge $30 to install a steerer plug. Buy a torque wrench and just pop it in and torque it up. Just make sure it's not below the stem.

The only weird system I know of are cervelos with a glued in metal tube and star fangled nut. I presume though if you have pulled it out it isn't like this.

I assume you're talking about the removable expander plug/cap (below), not the one with a star flange. Those are easy to do yourself, just use a torque wrench.

---

ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Noob question: The compression plug pushes out from the inside while the stem squeezes in from the outside. I'm guessing the torque prescription for the plug is such that the fork tube can handle the internal pressure without needing the reinforcement of the external pressure the stem provides right? If the pressures were really high, I suppose the prescription would be to alternate tightening each, so they were mutually reinforcing, to avoid the compression plug cracking the tube from the inside or the stem crushing it from the outside. Of course, I'm guessing the real concern is a combination of inappropriate installation and the forces generated during use of the bike.

You don't need a torque wrench.

Circles are really strong structures and you don't have to worry about breaking a steerer tube.

That is the purpose of the compression plug though, right?

That depends on how the fibers of the steer tube are laid up. I could make a super strong circle out of composites and I could make a very, very weak circle. If a torque wrench is available, I'd definitely use it. No real reason not to.

Do you mean, if you know how to achieve a certain torque range by feel?

Or do you mean, because it doesn't matter how loose or tight the compression plug is?

Those two are rather different.

Steerer tubes are made very strong.

You will know if it is too loose because it will pull up when you tighten the top cap.

It is only too tight when you strip it, and that is pretty hard to do.

The purpose of a compression plug is to hold the fork and headset inside the frame's head tube.

No, it's not. The purpose of the compression plug is to allow you to use the top cap to preload the headset bearings.
@niccolo: the normal order of operations is:

• Install the compression plug with its top surface about 8 to 10 mm below the end of the steerer tube. Torque to spec, or "just a bit beyond snug".
• Put together the steerer stack: Upper headset bearing, bearing cap, then the spacer and stem stack. The top of the stack should protrude about 3mm beyond the end of the steerer tube, once you've ensured there is no slack in any part of the stack. It is good practice to use a spacer right at the end of the stack so that the stem can't crush the end of the steerer tube when you tighten the pinch bolts.
• Align the stem and the fork, put the top cap (the preload cap) on to the top of the stack and tighten the preload bolt until the steerer has the right amount of preload. This does not take a lot of torque! If you can 'feel' the balls rotate in the steerer bearings then things are way too tight or else someone else has overtightened things before and wrecked the bearings.
• Now tighten the stem-to-steerer tube pinch bolts to spec.

At this point the stem holds the fork, headset and stem together. The preload cap is basically redundant at this point but you leave it in place.

---

Less is more.

Preload the headset bearings = hold the fork and headset inside the head tube

Gonna have to disagree with you on the semantics of that one, if that's okay with you.

---

Less is more.

That's ok with me.

Not semantics; this is flat out wrong. The compression plug preloads the bearings. The stem clamps on the steerer and holds the fork in place.

The stem can't hold the fork and headset in place without the compression plug and top cap doing their job first.

Sure it can. You could put the stack together without the cap and set the preload with a big F-clamp. Then tighten the stem pinch bolts, remove the clamp and you’re good to go. It’s just harder to get the amount of preload right that way.

---

Less is more.

I don't know anyone who would do that.

Follow your fork maker's instructions.

You've gotten differing advice in responses here, some good some bad.
Forks can and do break, some in response to an incorrectly installed (or removed) compression plug.
Forks have been recalled related to steerer/stem problems by several of the big names, so it is far from a simple. That's why it's important to follow your fork maker's specific instructions.

---

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

This is terrible advice / workaround that is actually known to contribute to carbon steer tube failure. Not only are you likely not preloading properly (leading to play in the fork), but you're also not using compression plugs help to support the load applied by stem clamps. It might have worked for alloy steer tubes, but those are far less common these days.

For the OP...Here's an interesting perspective on the utility of different compression plugs
https://www.youtube.com/watch?v=8bSnbjHiFXc

Of course it is (a terrible example) and it seems nobody is catching that I was not actually serious about doing it that way. I was making an extreme example to illustrate what the different parts of the fork and steerer assembly actually do, and most specifically, what the top cap does not do. The top cap has no function at all in actually keeping the assembly together once the preload is set and the stem clamps are tight.

Damon Rinard's advice is correct. Follow manufacturers' instructions and if it seems complicated, get someone who knows what they're doing to do it or to teach you.

---

Less is more.

I contacted Planet X (manufacturer of my bike) and they said they have no specific "instructions" for their forks/steerer tube/compression plug. Their response was "it should be straight forward to loosen and re position ".

I guess it should be OK to do it myself as long as I position the compression plug underneath my stem.