Threadless Stems: Basic Questions
 

I'm new to threadless stems, and even after a lot of googling I have some qeustions:

1. No Locknut. On my threaded headset, I'd adjust the play with the big nut and locknut. My understanding is that on the threadless system, this is done with the small hex bolt. Since there's no locknut, how is it that this stays put?

2. Loosened Top Nut. I removed the top nut and even took the top cap off, yet the adjustment of the headset stayed the same (that is, it didn't get loose). Is there something that needs to be tapped?

3. Stem above tube. On the used bike I just bought, the top edge of the stem is slightly above the steerer tube. Is that the way it's supposed to be? Should I fix that?

Thanks!

On a threadless set up, the cap/hex bolt preloads the bearings and the stem clamps that adjustment in place. With the top cap/hex bolt in place, loosen the stem bolts, adjust preload then tighten stem. The stem needs to be slightly above the top of the steerer tube to allow the preload to be set.

the top bolt is for tensioning or preloading the bearing. The two bolts on the stem basicaly replace the locknut. So if your stem is on top of your stack (spacers+stem) then it should be slightly higher then your steer tube. That allows you to pre load the bearings with the stem cap bolt. Tighten the stem cap bolt just enough to take play out than tighten the two stem bolts, they are what actually locks everything in place. Theoretically after the two stem bolts are tight you could take the stem cap off which would look bad but it should not allow the stem to loosen any.

1. Threadless headsets have no locknut. They rely on the downward pressure of the stem as transmitted through the bolt in the top cap to set their adjustment and then use the stem's clamp to hold the adjustment in position.

2. To adjust the headset you MUST loosen the bolts that clamp the stem to the steerer tube. If those bolts are tight, the headset can't be adjusted. Once you loosen those bolts, you then set the headset adjustment using the top cap's bolt. BTW, most threadless headsets recommend a slight preload of 4-10 inch pounds.

3. That small gap (2-3 mm is recommended) is not only normal but essential. There must be some room for the top cap to pull the steerer up to adjust the headset. If there is no gap, the top cap will butt up against the top of the steerer tube and no further adjustment will be possible. So, you either have to have the stem's upper edge slightly above the steerer's top or install a small spacer above the stem to give the needed gap.

Or what he said.

Thanks, you guys are great!

So, if someone wanted his handlebars lower, would he put one or more spacers on top of the stem?

Are all stems the same height (for the part that bolts onto the steerer tube), so that you can change stems without buying different spacers?

Stems vary in height, but not by much. So do spacers. You can lower the stem by rearranging the spacers like you suggest.

As noted, the steerer clamps on threadless stems do vary a bit in height and are typically in the range of 35 to 40 mm.

You have a couple of options for lowering the bars. One is to rearrange the spacers so there are shorter or fewer under the stem and place enough spacer(s) above the stem to keep the adjustment gap we discussed above. Second, if the stem is angled up, you can "flip" it over so it's angled down and reduce the bar height that way.

Also, if you don't like the appearance of spaces above your stem once you've lowered it, you can cut the steerer tube to trim off the excess.