I own a Cannondale Super Six 105 (Ultegra now) Carbon 2012 bike and I can't stop the wobble in the headset. If I tighten down the top cap (with 6mm hex) I can get rid of the wobble (hands on the drops holding brakes - headset has a fair bit of play) but I cannot move the wheels freely with the handlebars.

I stripped it down, cleaned it and assembled it again but its still wobbly after tightening the inner 5mm allen key.

Do I need a new headset ? It's KP044 I think.

The bearings move around nice and easy but the compression ring feels very rough to touch.

The bike is 4 years old, 30,000+km cycled on it, I'm not sure whats wrong -

(1) I didn't tighten properly (2) headset needs replacement or (3) bike is old and something wrong with frame.

Would a new KP044 fix it for me or could the bike be kaput ? Also if I cycle on (1-2 weeks) with a wobble will it do damage to the frame ?

Some pictures loosened these first

Spacers removed sits like this bearing top cap Compression ring - sits into bearing, feels rough

I don't know if the pictures are much of a help but everything is there except a bit of a rough corner feel.

  • To clarify, you loosened the stem bolts, tightened the bolt on top then tightened the stem bolts, right?
    – Batman
    Commented Jun 25, 2016 at 15:00
  • Yes - I loosened the stem bolts before I started to tighten the inside of the top cap (with the 5mm hex). I then tightened the top cap with the 6mm hex and finally tightened the stem bolts on the side. I tried a few times but always have the play when holding the brakes.
    – Aindriú
    Commented Jun 25, 2016 at 15:09
  • The top cap needs to be tightened until there's no play. After this you tighten the stem bolts. I'm still wondering about the 'inner' 5mm. Could we have a picture please?
    – Carel
    Commented Jun 25, 2016 at 19:19
  • 1
    If you have a carbon steer tube (which is looks like) the inside "star nut" should be a compression fitting. Rather than be hammered in place like a traditional star nut, it is tightened in place with a hex. That the singular bolt inside the steertube, under the top cap. Re tighten it (very tight) and never touch it again. It should be tight enough to hold the top cap for headset adjustment, varying the tightness on it is not necessary. Commented Jun 25, 2016 at 20:52
  • 1
    It's possible that if you rode it with a wobble for any length of time, that you damaged the bearings/races or some such and may just need to replace it. Commented Jun 25, 2016 at 22:15

3 Answers 3


It sounds as through you loosened the compression nut inside your carbon steer tube, which you should not have done. That bolt (the 5mm inside) should be tightened once during installation and is not touched for a headset adjustment (or than to perhaps check it is still tight). When you loosened that bolt, you made it so that the top cap will simply pull the compression nut up, rather than pull the fork and compress the headset bearings. Tighten the interior (the 5 mm inside) compression nut in place, then restart your headset adjustment process and hope that you haven't damaged the headset by riding it improperly adjusted.

Carbon Steertube Compression Plug

By comparison, a fork with a metal steer tube will generally use a star nut. enter image description here

These are hammered into place and will not move up. The metal wings cut into the tube and allow the top cap to compress the headset. This setup is inappropriate for a carbon steertube since it damages the carbon.


I had a similar problem with a recently serviced relatively old trek. When I applied brakes or did a bunny hop, I could feel the handle move around.
This may not apply to you since your bike is no where near as old as mine was but this was the problem with mine. The bearings in the tube had worn out significantly and dirt and grime had taken the place of metal. When I rebuilt it and removed all the dirt after it was sitting in my garage for nearly 3years unused, the gap became more noticeable.
My only choice was to replace the bearing. This might be your problem if you've not used it for a long time and you recently cleaned up the inside of it. Note: the compression bolt mentioned above did nothing to remedy the solution. So if it doesn't in your case too, the bearing might just have worn out from use and grime stuck inside prevented you from noticing it


I got the new bearings Thursday evening and once I installed and tightened the headset there was no wobble. new headset

I took the bike out on a 130km cycle Friday and the bike was like new, going around corners felt so much better/safer/solid. I didn't feel I had to even reach for the brakes so I must have needed a new headset way before now.

The LBS somehow managed to tighten the headset in the past when servicing the bike for me but I can't compare the two.

I didn't get the bottom bearing removed. It doesn't seem to come off too easily but its not causing problems.

The new Cannondale come with a plastic cover (left of the top cap) that seems to sit on the bottom bearing. Not for my 2012 model as its too small. There new compression nut that does a better job than the older model.

  • 1
    Good work and thank you for the followup. Once the timer has expired, please click the green tick/check box on the left side of this answer to mark it as "accepted"
    – Criggie
    Commented Jul 2, 2016 at 21:31

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