Headset not tightening...

I presume the stem clamp bolts are lose when doing up the top cap (as you don't actually say!).

How much below the top of the stem (or spacers) is the top of the steerer tube?

This is exactly what happened to me last night with my new Attain GTC, dropping the bars by exactly the same amount as you by the looks of it

You need to just lower the star nut inside the steerer tube a bit. Then it will all clamp down properly.

Or that silver bit needs to be lower, so if that will happen with the star nut lower, what the previous poster said.

Trust me, on the very same bike, doing the very same thing, last night, that is what fixed the problem.

It's not a star nut, it's an expanding plug, but it does need lowering. See the hex bolt in the top? Loosen that, push the silver bit down into the tube until the edges are flush, then tighten the hex bolt again.

lettingthedaysgoby wrote:

courtmed wrote:

Thanks for your help guys. Is it worth me lowering the star nut to see if that does make a difference? If so, how? otherwise I'll order a pack of spacers & give that a go.

Look down the top of the steerer tube, you'll see the thread that the cap screws into. Surrounding that is a hex shaped hole. Stick an appropriately sized Allen key in it, loosen slightly, and lower it about 3mm. Tighten it up again, and then put everything back as normal.

And when he says loosen slightly it is only slightly, if you overdo the loosening the bottom of the expander plug will come adrift and drop down the steerer tube. Looking at the pictures, the top of the expander plug has a rim which should be tapped down to be flush with the top of the steerer tube. Make sure you tighten the bung up enough so it does not pull back up when you apply tension with the top cap else you are back to square 1.

Svetty wrote:

If you have 1.5cm of spacers above the stem, the compression bung is unlikely to sit at the level of the stem. You'd be better cutting the excess from the steerer.

What? You do not need to cut the steerer. The bung needs moving down and tightening in position. Then use enough spacers to allow the top cap to pull the headset tight. If at a later date you find that you prefer the stem to be in a lower position and you are riding with a load of spacers above then it might be worth trimming the steerer to get rid of the excess. Again, you do not need to cut the steerer to allow adjustment.

The steerer length is fine, unless it's the world's shortest bung (and it's an alloy steerer anyway, and you don't actually need a bung to resist stem clamping forces - after all, Canyon don't have one on their carbon steerers, and you don't have a bung in your seatpost, do you?).

What's important is to ensure that the bung is snugly seated against the top of the steerer, that it has been sufficiently tightened so that the top cap bolt doesn't just pull it back out again (which is what has happened, looking at the pictures) and that there is a sufficiently large spacer above the bung so that the top cap doesn't bottom out on the bung itself. The spacer shown is too short. You will find that you need to tighten the bung more than you'd expect to resist the extraction force of the top cap bolt. This can be ...disturbing... in carbon steerers, but you won't hurt an alloy steerer even if you gorilla the bung expansion bolt.

Many (but not all) stem manufacturers recommend a 5mm spacer above the stem as a minimum, and leaving a bit of extra steerer isn't a bad idea if your stem is slammed, just in case you a) fancy selling the bike to someone less flexible than you or b) lose some flexibility or fancy a properly long ride at some point. Moving your stem up 10mm makes an amazing difference on a 300k ride.